The Synergy of Architectural Lighting with Sustainable City Development—A Case Study

Abstract

Designing the floodlighting of objects in the context of improving the night image of the city is a very complex task, requiring not only a time commitment but also precise analysis and innovative solutions. In particular, designers must consider the principles of aesthetics and adapt the lighting to the architectural style and details of the facilities while ensuring energy efficiency and minimising the impact on the natural environment. For single objects, the task is relatively simple. The problem arises when the task is to develop a lighting concept for a large ensemble. Computer applications strictly dedicated to lighting analysis cannot capture a 3D model rich in architectural detail. The article presents a case study that focuses on a comprehensive approach to designing the floodlighting of a complex of architectural objects. The steps for designing the floodlighting of objects are presented. Based on a computer simulation, a visual lighting concept and a detailed analysis of the luminance distribution and floodlighting efficiency were presented. The obtained average luminance levels are consistent with recommendations and standards, and the project is characterised by a high lighting efficiency of 56%. This approach enables an understanding of how light affects architectural structures and the surroundings, which is crucial to achieving harmony between the technical side of the project and its aesthetics. The project presented in the article is an inspiring example of how a comprehensive approach to illumination can contribute to creating an attractive night landscape of the city, taking into account the aspects of sustainable development. This is very important nowadays, when the floodlighting of architectural objects is often considered an element of the landscape that can be omitted.

1. Introduction

The aesthetics of lighting architectural structures in cities is a topic that is becoming more and more important with the development of civilisation in today’s world of urban planning and architecture [1]. The designer should consider the technical aspects of lighting in his work, such as the appropriate lighting intensity and luminance level, energy efficiency, and safety, and simultaneously create an unforgettable visual experience because this is the primary goal of floodlighting objects. We should witness the proper combination of aesthetics and technique when observing illuminated objects [2,3]. This is a massive challenge for the designer. A challenge that is not free from the risk of making mistakes. Using light, an object can be presented subtly, often with an effect similar to its appearance in daylight, or significantly changed by creating significant contrasts. It is also worth getting to know the opinions of outsiders not professionally involved in lighting technology and confronting these opinions with the assumptions of experts in this field, such as lighting designers and architects. The way ordinary people look at buildings certainly affects the well-being of residents and tourists. Such research on the perception of the city at night allows for the development of sustainable heritage management models [4,5]. It is essential that residents and tourists feel safe walking in the area and that buildings are not exposed to devastation in hazardous places. Currently, the issue of electricity consumption for the floodlighting of objects is also important [6,7]. Another problem is light pollution of the natural environment and light penetration into interiors [8]. These aspects are part of sustainable urban development strategies. The lighting designer, who is usually guided by the technical side of projects, becomes an artist who must have sufficient technical knowledge. It creates visual impressions, emphasises the uniqueness of buildings, and influences the recipients’ feelings. It is recommended that his work be consulted with architects and art conservators because they have the most excellent knowledge about the architectural perception of objects.

While in the case of individual objects, the issue is simple, in the case of an architectural ensemble, more factors must be considered. First, object assembly is usually more extensive; therefore, developing a project requires more time and a comprehensive approach to the task. The objects included in the complex may have different architectural styles, constitute one whole (objects connected), and may be of different sizes. They can also perform other functions.

This study aims to try to answer the following question: is it possible to design the floodlighting of a large complex of architectural objects in such a way that the effect combines the aesthetic features of lighting with the lowest demand for electricity and follows the recommendations for the illumination of objects? Following scientific publications, answers to these questions were not found. Of course, it can be imagined that the building’s façade is a flat surface. In that case, the calculation software can automatically select luminaires and their arrangement and aims to achieve the intended level of illuminance or luminance. We encounter such cases when designing interior or road lighting. However, when creating a lighting concept for a building, the designer first considers the facility’s architecture. Usually, the façade is not flat. When deciding to install lighting fixtures on the walls, the designer aims to accentuate architectural elements, e.g., windows, columns, pilasters, etc. He places the luminaires further away from the building if he wants to illuminate the facility with high uniformity. In such cases, installation locations are usually dictated by the existing lighting system, e.g., road lighting or the architectural surroundings of the building. In each of the described cases, this work requires the manual arrangement of luminaires. It requires several trials. This article intends to present the process of designing the floodlighting of an object based on computer simulation in the form of photorealistic visualisations. The analysis will take place on a large complex of architectural objects. Therefore, it is a practical work based on a case study.

1.1. Description of the Research Object and Scope of Research

The object of consideration is the complex of former government buildings at Bank Square in Warsaw. It is the centre of the capital of Poland (Figure 1) and one of the busiest places in Warsaw. Currently, it primarily serves as a communication hub, as the following two crucial arteries intersect there: Solidarności Avenue connecting the districts on the left and right side of the Wisła River and the main street in Warsaw running from south to north, i.e., Marszałkowska and its extension, Gen. Anders Street. Due to the very high traffic intensity, the remaining functions of the square are currently marginalised, even though it houses many offices, a museum, two monuments, shops and restaurants. The form of the spatial development of the square is considered a relic of the urban planning of the 1960s, which preferred the division of communication and residential functions, while currently, one of the goals of sustainable city development is to reduce traffic intensity in city centres. After World War II, it was planned to give this place a representative function and integrate it into the so-called Corazzian Axis, i.e., the urban layout that runs to Theater Square, where one of the Grand Theater and National Opera buildings is located, but this failed. The current city authorities are wondering how to bring out the beauty of this place’s beauty and its historical and tourist values. In 2023 alone, 10 million tourists visited Warsaw, but there is no analysis of how many visited Bank Square. There are many concepts for developing the square area [9]. They all strive to make it as environmentally friendly as possible. This results from numerous conversations with residents, surveys, and workshops. Currently, the greenery in the square covers only 4% of the total area, while the vast majority is covered with asphalt and concrete. This makes the place unpleasant to spend time in summer due to the temperature. However, it is subject to constant changes. This year, a bicycle path was put into use. New plantings have been made, but this is not the final solution.

The band also has a rich political history. It performed necessary government and administrative functions in the past, hence its name.

The palace complex consists of five buildings located in a row, wholly occupying the western frontage of the square. Their total length is almost 260 m. The height of the structures, measured in metres, ranges from 15 to 26 m. These are two-, three-, and four-story buildings, but these cannot be distinguished in terms of their cubic dimensions. Each of them is similar in this respect.

The first building, from the side of the city centre (Figure 2), is the former Stock Exchange and Polish Bank Building. It was the first seat of the Polish Central Bank. It is a late classicist, two-story building with a low dome crowning a rounded corner. This dome covers the circular, three-story bank operating room, decorated with coffers in the dome vault, sequences of figural reliefs, a two-story colonnade of the entrance to the rotunda, and galleries surrounding the interior. The ground floor is in the form of arcades. The building was built from 1825 to 1828, according to the design of Antonio Corrazzi. It was transformed in the 19th century, including bricking up the ground floor arcades. During the defence of Warsaw in September 1939, the building was damaged by bombing and rebuilt from 1950 to 1954 under the supervision of Piotr Biegański. Since 1989, the Museum of the Collection of John Paul II has been located here. The museum was created from the collection of Western European art gathered by Janina and Zbigniew Porczyński.

The second one from the right side (Figure 3) is the Palace of the Minister of Treasury. It is a three-story, late classical palace with a dynamically shaped body (resembling a monumentalised Renaissance Italian villa), with a triad of prominent avant-corps pavilions, the sides of which are only two stories high, equipped with viewing terraces. The facades of these three projections have the character of column arcade galleries connected with single-story column connectors. The building initially had 14 figural sculptures on the balustrades of three terraces, a figural group above the central avant-corps and platters on the edges of the attic. Only the frieze under the crowning cornice with motifs of gryphons and vases survived. The author of the project is also Antonio Corazzi. The palace was built from 1825 to 1830. During World War II, it suffered twice, in 1939 and 1944. Like B1, the palace was rebuilt from 1950 to 1954, also under the direction of Piotr Biegański.

The third building (Figure 4) is the former Palace of the Government Commission of Revenue and Treasury. It was built in the entré coeur et jardin type, with a semi-enclosed front courtyard. It is a late classical three-story building with a six-column Corinthian entrance of the main body supporting a triangular pediment with a tympanum. The main building is one floor higher than the others. The side facades, set at 90-degree angles and partly single-story, have four-column Ionic porticos facing the courtyard. These porticos are located halfway along the façade and are visible only from closer observation points. The whole is finished with monumental Ionic colonnades along the streets. In 1939, the palace was burned down and finally destroyed during the Warsaw Uprising in 1944. It was rebuilt from 1950 to 1954, also under the direction of Piotr Biegański. Currently, the building houses the headquarters of the Mayor of Warsaw, the Office of the Capital City of Warsaw, and the Masovian Voivodeship Office.

Next to the Treasury Palaces are the Heurich Tenement Houses (Figure 5 and B4 and B5 in Figure 6). The first one, on the side of the Palace of the Government Commission of Revenue and Treasury (B3), is a late classicist, two-story building topped with a triangular tympanum, with an even-numbered window axis, which is unusual for this style (Figure 5a). During World War II, it was only partially destroyed. It is considered one of the best-preserved tenement houses in Warsaw in the first half of the 19th century, so its architectural value is very high. Further houses, initially two (the second one on the side of Solidarności Avenue, Figure 5b), were built after 1792 and rebuilt and combined into one corner building. These are two-story tenement houses with Neo-Renaissance decoration of triangular pediments over the first-floor windows. The architect’s name is unknown, but there are speculations that it could have been Jan Kacper Heurich (son of the investor of the tenement house adjacent to B3). The tenement house underwent numerous transformations; after 1900, it had three floors topped with an additional storey with a mansard and an insert with a triangular pediment. The rhythm of the pediments of the first-floor windows was changed as follows: a series of straight segmental cornices, interrupted three times by triangular pediments. The tenement house, which was heavily damaged during the war, was rebuilt and lowered to a height of two floors.

Currently, palaces B2 and B3, together with tenement houses (B4 and B5) and a small part of the former headquarters of the Bank of Poland (B1), are internally connected and house the Provincial Office, the Council and Management Board of the Capital City of Warsaw, the Warsaw Center Commune Council, the Local Government Assembly of the Warsaw Voivodeship, and the seat of the President of Warsaw and the Voivode.

The technical condition of the facilities included in the complex resulted in the city authorities deciding to renovate. It was decided that the colours of the facility from years ago would be restored in a way that was most consistent with the original, i.e., the colours of the 19th century. Therefore, the renovation planned for the coming years is a very good time to consider the professional illumination of the complex. This will significantly reduce the costs associated with installing lighting fixtures in relation to an already renovated facility. This is a sensible approach.

The scope of the task included developing the floodlighting concept and its 3D visualisation, selecting lighting equipment and its mounting and aiming points, and checking the compliance of the concept with the recommendations regarding the floodlighting of objects.

1.2. The Current Floodlighting of the Objects

The location of the complex of buildings in the city centre and the richly detailed architecture of buildings B1, B2, and B3 by Antonio Corrazzi, despite the problems described in Section 1.1, attracts both Warsaw residents and tourists, unfortunately, currently, mainly during the day, because in the evening, the lighting of the complex is disordered at first glance (Figure 7).

Bank Square in Warsaw is lit with street-type luminaires in a mast system. There are decorative lanterns in front of the façade, along the entire building length from the square side. There are decorative candelabra in the arcades of buildings B1 and B2. Some lanterns and candelabra are extinguished due to their technical condition or wear of light sources. As a result, the arcades are not lit and are exposed to devastation, and people walking along the square after dark may feel unsafe. Police patrols can be seen very often in the square, both in the evening and during the day (Figure 4 and Figure 7c). Luminaires illuminate the Town Hall square in the courtyard on the side façade’s cornices, but they could be more effective. Floodlights were installed above the central entrance to the Town Hall, illuminating the portico’s columns. Their selection needs to be corrected, and the effect is barely noticeable. Looking at Figure 7c, it is hard to believe that luminaires are installed at the base of the columns. Additionally, image analysis shows that two of the luminaires, from the right and left sides, are broken.

The luminance level in the square and on the façades of the facility varies greatly. It ranges from 1.5 cd/m² on the façades of the City Hall courtyard to even 10 cd/m² on the ground floor of the B4 tenement houses. Therefore, it can be concluded that despite the luminance levels, which meet the recommendations for the floodlighting of objects, there is “luminance chaos”. The Town Hall (B3), the most important building in the complex architecturally and due to its function, is illuminated with the lowest brightness level (Figure 7c). Therefore, the principle of illuminating objects to enhance depth and height is unmet.

The Juliusz Słowacki Monument is flood-illuminated with two spotlights on street lighting masts. Due to the dark finishing material, such lighting cannot be adequate and is also not noticeable despite the high luminosity, which interferes with the brightening of the lower part of the façade of building B2 (Figure 7a). The illumination luminaires are placed relatively low. The result is a lot of glare and the creation of ugly, sharp shadows on the B2 building.

The current electricity consumption for this purpose of floodlighting is 8.5 kWh. Taking into account the effect obtained, it should be concluded that the lighting is energy inefficient. It also fails to fulfil its tasks; historic buildings are lost in the dark, and their surroundings are unpleasant and unsafe. This does not encourage visiting this place after dark.

1.3. Characteristics of the Main Points and Directions of Observation of the Object

Due to the current way traffic is organised at Bank Square in Warsaw, the architectural complex can be observed from many points and directions of observation. However, defining the main directions is crucial. This is where the illuminated object should look best. Figure 2 shows the current lighting condition of the object made from such places and directions. When analysing these images, attention should be paid to the relatively small angle of observation of the entire building for the observation directions from the city centre (Figure 7a) and from Solidarności Avenue (Figure 7b), where the subway station exit is located. In these cases, good visibility of the complex’s architecture is limited only to the two to three nearest buildings. Nevertheless, these points and directions of observation should be considered the most important.

The main direction of observation should also be considered the perspective perceived by the observer standing at the bus and tram stop opposite the City Hall (Figure 7c). In this case, to admire the remaining objects in the set, you have to turn your head, thus losing the opportunity to observe previously noticed objects. It should also be assumed that the illumination of the complex will encourage the observer to approach the building closer, especially to the City Hall gate as the central point, to become acquainted with both the method of illumination and the architecture of the façade deep in the courtyard.

2. Materials and Methods

Currently, designing the floodlighting of objects can be performed in several ways. Field trials can be carried out using real lighting equipment or simulations. Even though performing field tests is very objective because we can observe its lighting directly on the object, unfortunately, it only works for small objects. This is because the number of luminaires in such cases is relatively small. The methods of mounting the lighting fixtures and the lighting concept are also essential. In the case of mounting luminaires on a façade or from a great height, the undertaking of field tests is quite complicated and expensive, regardless of the size of the facility. In the case of a large architectural assembly, the field trial method is even less effective. The number of luminaires provided for in the lighting concept often significantly exceeds the availability of actual luminaires to perform such tests. This is the case even with large lighting companies. The only correct solution in such cases is computer simulation. Currently, we are dealing with an extensive range of advanced computer applications and computational algorithms [11,12]. Therefore, lighting design can be performed in a way that seemed impossible not long ago, and the designer has a wealthy library of tools. It should be noted, however, that with this wide range of devices, when designing lighting, they must be selected very carefully.

To achieve this correctly, the designer must answer a few key questions:

• Does the computer software allow you to recreate the model realistically or load a ready-made model created in another way, for example, 3D scanning?
• Does the software enable defining the reflection and transmission properties of materials?
• Is the tool used to allow you to load photometric data of luminaires?
• Does the software calculation algorithm take into account photometric calculations?
• Is it possible to analyse lighting in the software?

A positive answer to all these questions will help the designer select only those tools that can be used to simulate lighting. In the case of floodlighting designs, there is often another factor. Is it possible to develop a photorealistic design, especially when the facility is huge? Several tests involved loading advanced geometric 3D models into several applications. Unfortunately, they were unable to support these models. The large amount of architectural detail made it impossible to load them. When this was possible, computational problems arose. So, it was decided to use the Autodesk 3ds Max 2022 software. It is a popular, validated [13] tool in many scientific studies and projects [14,15]. It allows the designer to create virtual space models, define various light sources, even those that seem complicated and linear [16], and then analyse how light will behave in natural areas. The user can, at any time, find out about the level of illumination or luminance at individual points of the illuminated surfaces and average values in specific fields. This is, from a design point of view, a significant factor. It eliminates the need for additional computational software explicitly created for lighting. Illuminance or luminance distributions can be presented in a numerical grid applied to a given illumination image and as an object raised on a colour scale with an appropriate legend, the so-called false colour image. A considerable advantage of the application is the photorealism of the calculation results in the form of visualisation.

However, checking whether you can trust 3ds Max for photometric calculations is essential. For this purpose, a simulation was performed for a small part of the simple object, and the results were compared. For simulation, it was decided to use the most sensitive positioning of luminaires—diagonally to the façade. Figure 8a shows a computer simulation made in the DIALux evo 12 software, and Figure 8b shows a simulation made in Autodesk 3ds Max.

Both images are taken with the same exposure and using the same model and material properties. Analysing these simulations, it should be concluded that the results in both cases are the same, and the Autodesk 3ds Max software can be used in further lighting simulations. Both software allow you to generate a false colour image. Unfortunately, these images differ in tonal range, so comparing them and drawing conclusions on their basis is very difficult (Figure 9). Fortunately, the numerical analysis gave the same results. In each case, the average luminance for the entire object was 4.1 cd/m².

Based on the data obtained, it was found that the Autodesk 3ds Max software, although dedicated to computer graphics, is sufficient to develop floodlighting designs. In the case of very geometrically advanced models, it will perform photometric calculations and lighting analysis without any major problems

3. Results and Discussion

This chapter will show the process of designing the illumination of a large set of objects. This is a universal approach; it does not depend on the tool used, but the order of steps may vary.

3.1. Creation of the Geometric Model

Three-dimensional geometric modelling is the first, extremely important stage of creating a lighting project, especially when it is based on computer visualisation. Depending on the tool used, it allows for the exact geometry mapping of both real objects and newly created ones.

During computer modelling, each real object has its representation in virtual space, consisting of several vertices connected by edges. The set of these edges creates planes, which in turn, create solids. There are many methods for creating complex geometric objects. They depend not only on the type of software but also on the user himself. A simple ball can be made in several ways (parametrically by specifying a radius or using appropriate modifications, e.g., the rotation of an arc around a straight line), and the more complex the object, the more and more methods appear. However, it would be best if you always strived for a certain optimum—why cut out cornices in the façade separating individual floors or add them to a flat wall when you can draw a side profile (a cross-section of the wall) and stretch it to the appropriate length? All that remains is to cut out the window and door openings, insert previously created models, and prepare the simple façade.

Further methods appear as you learn three-dimensional graphics software and theoretical issues. Unfortunately, it is challenging to create, in a simple way, most of the ornaments found in architecture, such as bas-reliefs, column finials, or even a fence composed of a series of twisted metal rods. This is when more sophisticated design methods based on extrusions, logical operations on solids, and procedural modelling come in handy.

Another approach to creating a 3D model is scanning, which involves obtaining point data that are then transformed into surfaces. Yet another method is photogrammetry [17,18], which is based on a series of photographs taken from different directions. In the case of the discussed assembly, the classic method of making the model was chosen. The project’s technical needs, such as photometric calculations, dictated this choice. These calculations are a process that requires significant computing power, so the 3D model should contain as few planes as possible but reproduce reality as much as possible. This is a compromise between the quality of the model and the number of planes. The 3D model resulting from scanning would be very accurate, but photometric calculations might be impossible.

The appropriate way of displaying model data is also essential for design. Here, computer programs work very similarly. Almost everyone can view created objects in various projections (also simultaneously), parallel and perspective, and develop cameras with fundamental parameters of focal length and viewing angle.

Therefore, the possibilities offered by current software in terms of geometric modelling and the way of presenting a given model are huge, and their accuracy and parameters correspond entirely to the real environment perceived by humans.

However, it should be stated that the method of creating an object in the case of lighting simulation does not matter. The geometric model must be error-free so that the results of photometric calculations are correct, but above all, they are feasible from an IT point of view. In the case of the described architectural assembled objects, the classic method’s modelling process was successful. Figure 10 shows the final three-dimensional geometric model viewed from different directions. This is undoubtedly the most time-consuming stage of work. Developing the model took approximately 500 person-hours. This has to do with the number of planes needed for virtual reproduction. There are over 2 million of them. The 3D model was made with great care because it will be used to analyse lighting, especially lighting efficiency. It was made based on architectural layouts but also on photographs of details because the drawings never represent the actual structure.

3.2. Reproduction of the Reflection and Transmission of Materials

Once the geometric model of a given object, for example, a façade, has been created, it remains to determine the appearance of the surface. This is information about how a given object should react to light sources in the scene. This requires the user to use a mixture of physical parameters taken from reality and practices from the virtual world. The most crucial surface parameters are its colour, saturation, structure, and reflection (transmittance) properties.

To properly understand the principles of the operation of computer graphics software, it is necessary to refer to the appropriate phenomenon of the external world. The colour of an object is nothing more than the effect of reflected light. When light rays fall on a physical surface (e.g., orange fruit), the surface’s pigment absorbs part of the light spectrum, and the remaining amount is reflected and returned to the observer (orange). Therefore, the reflected portion of the fair range creates the primary colour. However, if you look at a given surface, there are also others that, when perceived by the eye and interpreted by the brain, give an idea of the structure of the character. A more thorough surface analysis also allows you to notice delicate patterns of darker colours, which the brain interprets as shadows resulting from the surface relief. All these parameters have their equivalents in computer graphics.

In the case of the discussed assembly of architectural objects, the investor’s (city authorities) decision was to reproduce the object’s colours from years ago. Research work in stratigraphy was carried out at the city’s request. As a result of this work, the eight most essential material samples were selected (

Table 1. Material samples were selected as a result of stratigraphic research.

Sample No.	Colour Visualisation	Colour Code
1		S1515Y30R
2		S0515Y20R
3		S0510Y20R
4		S0907Y30R
5		S0505Y20R
6		S1502Y50R
7		S1002Y
8		S8002R

). The remaining elements of the façade will be made in white without specifying a colour code. Figure 2, Figure 3, Figure 4 and Figure 5 show buildings in their current colours (June 2024). Despite being renovated in recent years, each will change according to the new colour specification.

The Autodesk 3ds Max 2022 software allows you to define the material very precisely [19,20]. In addition to the colour, the user can specify the gloss of the material and correct the reflectance if the application calculates a different value based on the colour. It should be noted that it was decided that adjustments to the reflectance over time would not be taken into account. It was a joint decision with the architects because the colour diversity of the objects is small, and the luminance levels are already high. Additionally, the assumption was to use luminous flux control, and after the illumination, its initial reduction was planned. Due to the nature of the place and facility, dynamic effects are not expected to be created. Still, such an implementation is always possible using an additional control system without changing the electrical installation.

Then, the geographical location of the object was mapped, and photometric calculations were made using daylight. The aim was to check whether the materials fit together correctly and whether the geometric model of the object had no errors. The photorealism of the simulation did not matter much. Figure 11 shows renderings of subsequent objects in the assembly from different points and directions of observation for the new object colour defined.

3.3. Lighting Concept, Photorealistic Simulation, and Analysis of the Impact of Lighting on the Environment

Building lighting plays a vital role in shaping the identity of the place where it is located. Characteristic illuminated towers or bridges or unique lighting effects on modern buildings can become a symbol of a given city or region. Designing lighting with local culture, history, or architectural character in mind allows you to create a unique identity that influences how a given area is perceived. Floodlighting an object is not about uniform lighting with the highest possible brightness level. It is a play of chiaroscuro. In inappropriate lighting conditions, shadows on the façade become as important an element of the composition as light, giving the structure three-dimensionality and depth. The harmony between light and shadow can create a visual spectacle that fascinates and delights. Uniform lighting, or instead avoiding it, is also essential. Therefore, the illumination concept should be carefully prepared so that the final effect satisfies and does not make the lighting feel boring.

The floodlighting concept of the Complex of Former Government Buildings in Warsaw was based on the following analysis:

• The possibility of limiting the installed power to a minimum;
• Basic directions of observation, taking into account distance;
• The reflection and transmission of the materials from which the object is to be made in the future;
• Existing lighting of the square by street luminaires;
• The surroundings of the buildings with the assumption that it may change;
• Architecture and function of the objects;
• Lighting recommendations and rules for floodlighting objects and groups of architectural objects;
• The possibilities of placing and mounting lighting equipment;
• Dimensions of luminaires.

The assumption of the project was to eliminate the existing illumination solutions for the facility and to illuminate all facades using the planar method [21,22,23] without unnecessary contrasts. This floodlighting method results from conservation recommendations and arrangements with architects. It also results from the recommendations of the International Commission on Illumination (CIE) regarding the floodlighting of objects. Indeed, an object can also be observed from close observation points, but distant points predominate, or the observation directions are at a slight angle in relation to the façade. In such cases, despite even a close observation point, the accents on the façade will not be visible. Another argument for choosing this lighting method was the awareness of the changes planned in the square. Until now none of the variants has been accepted so far, but each assumes introducing as much greenery into the space as possible [9]. It should, therefore, be assumed that the visibility of the facility in its current form will be limited, and the introduction of light accents on the facades may no longer be noticeable.

The planar lighting method, by definition, creates an evening image of the object similar to daylight. The facades are then lit relatively evenly; thus, their exposure reflects the effects intended by the architect. This is a sufficient reason to always consider this concept as the best and simplest to implement. This is often a misleading point of view. It must be remembered that surface lighting unnecessarily illuminates the interior of rooms through window openings. It also poses the most significant risk of glare and light pollution in the natural environment. The luminaires are mounted relatively close to the façade in the described case. The possibility of installing luminaires only in these places resulted from the design assumptions, which excluded their installation on the façade. To achieve an even distribution of luminance, the optics of the lighting equipment must be carefully selected. Unfortunately, architectural lighting design is not an automatic process. The computer software will not select the correct luminaires from the database nor indicate the targeting to achieve, for example, the recommended luminance level on the façade. The designer is, therefore, forced to place them and perform a series of tests manually. The number of iterations is more significant when the luminaires are closer to the façade because the luminance distribution is more sensitive to the optical system used in the luminaire. However, installing luminaires close to the façade has many advantages. Typically, the installed power needed to complete the task is lower, and the lighting efficiency is higher. When using this concept, the final effect often needs more image depth because all surfaces have the same brightness. The image of the object often needs more features of local exhibitions of architectural details. Its main attraction is the contrast with the dark sky. Therefore, implementing a project using the plane method should be approached in the same unique way as in the case of a technique emphasising architectural detail.

In the case of the architectural complex of former government buildings and tenement houses at Bank Square in Warsaw, it was decided to use primarily existing streetlamps along the buildings and street lighting masts as places for mounting lighting equipment. While the decorative lanterns are relatively close to the façade (6 to 10 m), the square lighting masts are far from the buildings (30 m). When making this decision, the square’s revitalisation plans were also considered. Only one square lighting mast was used to floodlight the top part of building B1. However, if this mast is eliminated, it will be easy to find another lighting solution for this architectural element of the B1 building in the future. In the case of the City Hall courtyard case, the luminaires were installed in places already connected to electricity. Figure 12 shows a plan for the arrangement of luminaires according to the developed concept, while

Table 2. List of luminaires used in the computer simulation.

Designation in the Project	Power [W]	Luminaire Luminous Flux ϕ [lm]	luminous Flux of All Light Sources ϕt0 [lm]	Maximum Luminous Intensity Imax [cd]	Optic δ1/2 [deg]	Quantity [pcs.]	Manufacturer/ Catalogue Number
A	34.7	2372	3650	2294	Wall Washer	34	Iguzzini/P847_A40J
B	15.6	648	1200	37,366	SuperSpot 4/6	4	Iguzzini/EI65_B89T
C	21	2407	3050	4258	Wide Flood 48	16	Iguzzini/E153_A46K
D	35	2372	3650	5972	Wall Washer	4	Iguzzini/P869_A44J
E	56.5	6840	8550	20,677	Flood 30	4	Iguzzini/BV03_LW72
F	91.9	9994	13,150	104,787	Spot 12	6	Iguzzini/E982_A53U
G	56.5	6840	8550	11,975	Wide Flood 46	1	Iguzzini/BV05_LW72
H	91.9	11,033	13,150	18,790	Wide Flood 44	10	Iguzzini/E986_A57U
I	27.2	3040	3800	20,750	Medium 16	5	Iguzzini/BX15_LC43

lists the lighting equipment used. The developed lighting concept took into account the recommendations of the International Commission on Illumination (CIE) regarding the floodlighting of objects and the recommendations of architects. It also resulted from the recommendations of the Warsaw Conservator of Monuments, who recommended lighting without lighting accents on the façade. The arrangement and selection of lighting equipment are not accidental. Luminaires with different power and luminous intensity distributions were used, so the luminance distribution on the facades was not equal, but the average for each building was similar. The calculations took into account the geographical location of the facility and the time of year and day. This is important when creating a collage with evening photography, which was the project’s intention.

A virtual scene created based on a 3D model with assigned reflection and transmission properties of materials allows for the free positioning of virtual light sources and photometric calculations. The calculations result in photorealistic visualisations. Despite numerous advantages, simulations have limitations and features, with 84 luminaires used in the project and a rendering resolution of 6000 × 2000 px. The average photometric calculation time per image was approximately 2 h; calculations are more time-consuming than they were a dozen or so years ago. This, of course, depends on the object’s size, the number of luminaires and the resolution of the final image. However, care must be taken to expose these images. They will be perceived completely differently in daylight on prints than displayed from a multimedia projector in a darkened room. The perception of the effect of using virtual reality glasses will be different too [24,25,26].

Figure 13 shows renderings taken from the main viewing directions. The project aimed to create a lighting system that ensures safety at night and enhances the aesthetics and harmony in urban space. The idea was to create a place to evoke positive emotions among residents by encouraging them to spend time outdoors and encouraging the unique architectural features of this complex of buildings. However, it was important that this would be achieved subtly. This goal has been completed.

The project considered the risks of using the planar floodlighting method, which is reflected in the differences in luminance levels on individual building facades. This resulted in accentuating the edges of the walls and shifting the façade. Those located more profoundly and higher and those more critical from an administrative point of view (Town Hall) are illuminated with a higher level of brightness (Figure 13c). This variation in brightness enhances the perception of architecture. The average luminance values in the Town Hall courtyard (Figure 13d) are L_avg = 20 cd/m², with an additional increase in the values for the tympanum and portico. The colonnades of the Town Hall were highlighted by the contrast of dark columns on a light background. The differences in luminance levels also highlighted the offset facades of the B2 building and the drum of the B1 building (Figure 13a). The lighting of the Juliusz Słowacki monument was not changed, but its shape became visible as dark against a light background. On the Solidarności Avenue side, spotlights were installed in the spaces between the columns of the B5 building (Figure 13d), emphasising architectural details.

The project used luminaires made in LED technology with a correlated colour temperature (CCT) of 3000 K. It is a warm colour that combines very well with the new colour scheme of the facility. The luminaires have a high colour rendering index (CRI) of 80. However, it should be remembered that the colour of the new façade will be different than in daylight conditions, in which the colour temperature is 6000 K, due to the use of warm light. Is this a defect? Should you use a high colour temperature? The answer is “No”. The purpose of floodlighting is not to reproduce the effects of daylight. Additionally, during the implementation of the project, the impact of the lighting of the complex on the surroundings was taken into account at each stage. Currently used electroluminescent sources (LED), especially those with high colour temperatures, have a much more negative impact on the natural environment. Compared to discharge sources, they brighten the sky and attract fauna, especially insects, to a large extent. Light pollution in Warsaw is estimated to have increased by 20% over the last seven years [27]. This is very disturbing information, and efforts should be made to stop further growth.

This project, therefore, includes various elements combining modern technologies and artistic creativity, but also cares for the natural environment and the surroundings of the buildings. The demand for electricity consumption for this purpose is 3.6 kWh. It can be said that this is a high value, but considering that currently, the candelabra along the complex’s buildings consume 7.4 kWh of energy, this project assumes the replacement of light sources and savings of 50%; it can be said that only this modification will allow for the balance of complete power consumption for the entire project implementation. Interestingly, this is performed without compromising the luminance level of the pedestrian route, which is already very high. It was decided to leave the lanterns as a decorative element and as a basis for installing new luminaires. Therefore, this floodlighting design is a perfect example of showing a comprehensive approach to a project, with a thorough analysis of the current level of electricity consumption and the modernisation of currently used lighting solutions. This allows for the effective use of modern light sources and positively impacts the natural environment while, at the same time, beautifying places in the city.

However, it should be remembered that photorealistic visualisation can never be an element of the lighting assessment. It is usually presented on screen or in print under different lighting conditions. In such a situation, the human eye cannot assess whether the design assumptions are met. In the case of floodlighting of objects, the analysis of their definition is based on the luminance distribution. Using the false colour technique, the luminance level can be checked numerically and in raster images. Figure 14 shows the luminance distribution from the main points and observation direction. The visual analysis of these images shows that the average levels of luminance of individual elevations are similar.

The assumption of the project was a solution that achieved an average luminance of L_avg = 12 cd/m², which is consistent with the recommendations of the CIE Technical Report, Guide for Floodlighting [22]. An analysis of these images shows that the average luminance level is consistent with the assumption. The average luminance of subsequent buildings along Bank Square is even; none stands out as it does currently by night.

Looking at the building from Solidarności Avenue (B5 in Figure 6), we can see higher luminance levels in its colonnades. This is a deliberate attempt to create depth in the image and to highlight the colonnade. Analysing the same image (Figure 14b), you can also see an increase in the luminance level of the B4 building, but this is mainly due to the light colour of the façade, which will become dirty over time and equalises the reflectivity of other buildings. Street lighting also influences this level, which we decided not to change. The increased luminance level on building B4 in Figure 6 can also be observed in Figure 14b.

Only the light sources in the candelabra in the building’s arcades and the decorative lanterns along the entire façade have changed. An increase in luminance levels can also be observed in the case of the portico in Figure 14d. In this case, the levels may appear to be exceeded, but this is only a point. Autodesk 3ss Max software also enables the numerical analysis of individual objects. However, the geometric model must be prepared appropriately. The surfaces/solids that make up the geometric model cannot interpenetrate. This is not software-specific. This is a general recommendation for such an analysis. The interpenetration of objects causes lower results because surfaces/solids inside another solid would have zero illuminance and luminance values.

Table 3. Measurement results for individual buildings of the complex of former government buildings at Bank Square in Warsaw.

Surface area	S	[m2]	3140
Average luminance level	Lav	[cd/m2]	11.87
Average reflectance factor	ρav	[-]	0.45
Average illuminance level	Eav	[lx]	82.83

shows the measurement results for the complex of former government buildings at Bank Square in Warsaw.

It should also be noted that a digital multiplex (DMX) protocol control system is provided for the entire project. This will allow for the dynamic adjustment of the value of the light flux, also considering the change in reflection parameters over time so that the luminance throughout the entire assembly is always equal, regardless of the object’s condition. However, the primary assumption of the control was the possibility of implementing various lighting scenarios. The facility may be illuminated with different luminance levels on weekdays and holidays. Similarly, the courtyard of the Town Hall itself is where various celebrations can be held, e.g., those related to the political function of the buildings.

This solution also provides the opportunity to reduce electricity consumption. It should also be noted that in the late evening and early morning hours, floodlighting is not required at the designed luminance level due to the low traffic in the city. A similar situation may be indicated at different times of the year. Assuming that the revitalisation of Bank Square is carried out and many trees appear there, lower luminance levels will be sufficient in the autumn and winter seasons. It is also possible to turn off individual luminaires.

Numerical analysis also allows for the assessment of the floodlighting utilisation factor (FUF). This is a parameter that has a direct impact on the impact of lighting on the natural environment. Unfortunately, currently, the science publications on the subject do not define the recommended values of the FUF. The categorisation of the designs and implementation of the floodlighted objects is also still being determined. The general recommendation is to strive for as much fitness as possible. However, design practice shows that a floodlighting utilisation factor value above 50% is considered very good.

The floodlighting utilisation factor is defined based on the following formulas:

$$\mathrm{FUF}={\displaystyle \frac{{\mathsf{\varphi }}_{\mathrm{u}}}{{\mathsf{\varphi }}_{\mathrm{t}0}}}·100\%$$

(1)

ϕ_u = E_av·S

(2)

where

• FUF is the floodlighting utilisation factor;
• ϕ_u is the luminous flux performing the average illuminance E_av on the object;
• ϕ_t0 is the luminous flux of all light sources installed in the luminaries used to illuminate the object;
• E_av is the average illuminance level on the object;
• S is the surface area of the object.

Based on the data in Table 3, the surface area of the entire object is S = 3140 m² floodlighted area, the average illuminance level is E_av = 82.83 lx, and the total luminous flux of all light sources is ϕ_t0 = 464,450 lm.

Based on Formulas (1) and (2), it can be calculated that the floodlighting utilisation factor for the entire complex of former government buildings is 56%. This value should be considered very good. It is influenced by carefully selecting lighting equipment and its arrangement so that the luminous flux reaches the object as much as possible

The high electricity consumption for illuminating Bank Square resulted primarily from lighting the pedestrian route along the facility. These luminaires indirectly influenced the façade’s lighting but caused considerable uneven luminance. The current demand for electricity for lighting the complex of architectural structures at Bank Square in Warsaw has decreased from 8.5 kW to 3.6 kW without compromising pedestrian safety and improving the aesthetics of the complex of former government buildings.

The presented renderings, both photorealistic visualisations (Figure 13) and luminance distributions made using the false colour technique (Figure 14), sparked several discussions. Initially, the two side colonnades in the Hall Town courtyard (Figure 13d) were lit from the inside using luminaires installed at ground level. However, consent to such an implementation was not given for technical reasons related to the need to supply electricity to these places.

Is this how the lighting designs for famous objects worldwide were made, for example, the floodlighting of the Louvre in Paris [28]? It is difficult to answer this question, but it should be assumed that the lighting design had assumptions similar to those in the complex of former government buildings in Warsaw, i.e., lighting without unnecessary contrasts. The lighting design of the objects in Warsaw was determined by the points and directions of observation and planned changes around the facility. The facades of the Louvre are not covered by anything, and the observation points are close, so introducing light accents on the façade could be an exciting solution. Nevertheless, the floodlighting of the Louvre is very successful. The resulting lighting effect is artistic and emphasises the seriousness of the object.

A completely different approach is presented by the lighting of the architectural complex on Stanislas Place in Nancy [29]. In this case, the buildings can also be observed from many observation points and, above all, from close up. However, the lighting concept is different. It assumed the accentuation of architectural details. The pilasters and the attic were emphasised. Was a photorealistic simulation performed in this case? It is also hard to say. However, it should be assumed that photometric calculations were made because this lighting method is more complex and can result in many errors. The effect obtained in this case is entirely different from that of the Louvre and the architectural complex in Warsaw, but it cannot be denied that it is attractive.

These two examples show how difficult the work of a floodlighting designer is. The architectural object can be illuminated in many ways, and not everyone will always like the effect achieved. Therefore, an individual approach to each project is essential, including a discussion with architects, the investor, and sometimes an independent environment, e.g., by conducting surveys. It is necessary to create a lighting project in the form of an image and, at the same time, present technical parameters.

4. Conclusions

Floodlighting objects is a spectacular work intended for a long time. It is always a unique opportunity to enliven and highlight the special features of architectural structures and urban spaces. The project could not have been a coincidence in the case of a representative building like the complex of former government buildings at Bank Square in Warsaw. The first stage of work on the lighting design was material analysis. This required stratigraphic research carried out by a team of architects. Then, a detailed geometric model of the facility and a daylight simulation were made. The goal was to check the composition of the selected materials. The scene prepared in this way became the basis for electric lighting simulations. Developing its lighting design was quite a difficult and time-consuming task, requiring appropriate tools and the interdisciplinary cooperation of the lighting designer. This project aimed to illuminate the facilities using a planar floodlighting method with the least possible interference of the existing power system in the facility’s structure. Existing street pole luminaires along the buildings were used, and the type of the new luminaires and their targeting at the facility were carefully selected. Collaborating with architects, we created unique and inspiring visual effects using technology, aesthetics, and a sustainable approach to energy efficiency.

The developed floodlight design of the complex of government buildings in Warsaw is coherent. The average luminance levels on each of the objects are equalised. The illumination method used allows us to conclude that this is a universal project, regardless of what the development of the area at Bank Square will look like in the future. The results obtained and presented in the article allow the viewer to be transported to an entirely new world, emphasising the importance and beauty of this place in Warsaw. They will encourage residents and tourists to visit this place by evening and night.

The project analysis presented in the article shows that thanks to modern solutions, such as LED technology, even a large complex of architectural objects can be lit in a less energy-intensive way than before it was developed. This situation applies to the façade facing the square. This is because urban spaces are often still lit by a system of streetlights that could be more energy efficient. Illuminated facades of buildings reflect the luminous flux, decorating the surrounding area, especially in facades made of materials of bright colours. The luminous flux reflected from the façade is often sufficient to ensure an appropriate lighting intensity on the sidewalks in front of the facility. This aspect should always be taken into account when designing the lighting of pedestrian routes. A thorough analysis of the illumination of architectural objects is a critical point in the design process. It allows you to create harmonious, energy efficient solutions, avoiding mistakes and using the potential of architectural lighting. The achieved floodlighting utilisation factor of 56% is a very good result, which will have a limited impact on light pollution and the natural environment. Using a control system will allow the implementation of various lighting scenarios. These may be changed due to different circumstances, seasons, or even nights.

To sum up, the goal was achieved, but it should also be remembered that this is a specific case study. It may turn out that for another set of objects, it may look completely different, but this also confirms how important a role computer simulation, especially a photorealistic one, plays in designing the floodlighting of objects, using appropriate tools.

They must be selected appropriately for each project. For small facilities, software dedicated to lighting design and analysis is a perfect solution. In the case of large and architecturally complex objects, unfortunately, one would have to look for other tools, but always check whether the calculation results are correct.

Using the Autodesk 3ds Max software, you can find out about the levels of illuminance or luminance in the form of false colour distribution and in a numerical way. However, the geometric model must be prepared appropriately in the latter case.

The limitations of computer simulations should also be kept in mind, regardless of the software used. In most cases, programmes do not consider the material’s spectral reflectance. Therefore, it is impossible to precisely analyse an object’s colour after illumination with a light source with a known correlated colour temperature and colour rendering index. It should also be remembered that the floodlighting of an object is, in most cases, assessed based on visualisation. This medium can be presented in both electronic media and print. The same image can cause different visual impressions in the same person. The solution is to use a false colour image. Their assessment is precise but sufficient because the recommendations regarding the floodlighting of objects provide average values for the entire object seen from a given direction of observation.

The case study presented in the article shows that developing such an enormous design task as a photometric computer simulation for complex architectural objects is possible but very laborious and time-consuming. It is like this because it requires the development of a very complex geometric model, and it is impossible to use automation. However, this approach should be supported because floodlighting is an activity on the border between technology and artistry. Therefore, the obtained effect should be technically correct and as photorealistic as possible.

Using simulation software will enable you to assess the extent to which the standards’ recommendations are met and reduce the power of existing lighting solutions. As a result, there is a significant improvement in the aesthetics of the city while minimising the impact of lighting on the natural environment and reducing operating costs. More friendly and inspiring urban spaces are being created, an example of which is the project discussed in the article.