*4.1. Classroom Lighting and Energy Saving*

Mareno and Labarca (2015) [72] have suggested that the traditional daylight analysis methods provide very limited information compared to the new dynamic methods that integrate factors such as sky type and local light conditions. These methods reinforce the evaluation of applied daylight strategies in favor of integrated design. This is shown in the design of classrooms by the method of dynamic simulation, which provides quantitative information on the proposed strategies, taking into account the levels of illumination for the visual tasks of the students.

The methods and metrics that incorporate climatic variables have been studied in order to refine the climate data needed to apply dynamic methodologies. Climate-based daylight modeling (CBDM) allows the integration of different variations of light in the simulations in relation to the local climate, generating for a specific moment a series of predictions which, in general, are for each hour of a complete year. At the same time, passive design, as an architectural principle, seeks to provide comfort conditions within buildings by optimizing the design through the integration of environmental factors of the site, thus minimizing the use of active means for that purpose. Complementarily, design for energy efficiency seeks a specific purpose for it, providing the best environmental conditions to achieve visual comfort and good lighting quality, and using the least amount of energy possible.

From the perspective of architectural design, a poor conception of lighting strategies can have negative implications, such as increased use of alternative energies, or can directly affect users, creating situations of visual discomfort. Dynamic metrics based on climate data (CBDM) have created a new perspective in the study of natural light by responding to the local climate, which accounts for daily and

seasonal variations of daylight when combined with weather data. These have displaced traditional daylight metrics, like the daylight factor (DF), whose limitation is that it does not consider the dynamic aspects of light: the latitude, the different seasons, the different times of the day, the variations of the skies, and the orientation of the building [73].

The metrics developed and used in dynamic daylight performance measurements are based on the time interval in which the basal levels of illuminance and luminance are reached within a building. These time intervals typically extend throughout the year, based on external data such as annual solar radiation and depending on the location of the building [10]. Among the metrics whose analyses are based on the time variable, we have daylight autonomy (DA), useful daylight illuminance (UDI), and continuous daylight autonomy (DAcon), which have been given a more comprehensive evaluation based on climate files, the building's orientation, and the time that the building is occupied. Daylight autonomy (DA) sets an illumination value to guarantee autonomy to work only with daylight; however, we can have an exceptional autonomy without guaranteeing visual comfort, since by not setting an upper illumination limit, we can have too much daylight at certain times of the year.

The useful life of daylighting defines a range of illuminances that can be said to constitute useful levels of illumination [74]. What is new about this metric is that upper and lower limiting illuminance values are incorporated, while compliance intervals are set by integrating the concept of target ranges. The new series defined in 2012 were the useful daylight illuminance (UDI) "fell-short" (UDI-f), when the illuminance is less than 100 lx; the UDI supplementary (UDI-s), when the illuminance is greater than 100 lx and less than 300 lx; the UDI autonomous (UDI-a), when the illuminance is greater than 300 lx and less than 3000 lx; the UDI combined (UDI-c), when the illuminance is greater than 100 lx and less than 3000 lx; and, finally, the UDI exceeded (or UDI-e), when the illuminance is greater than 3000 lx [75].

Al-Khatatbeh (2017) [76] stated that in classrooms, light levels are directly related to energy consumption due to the use of artificial light. Therefore, this study aimed to improve visual comfort and energy efficiency in existing classrooms by investigating various adaptation methods for passive daylighting techniques in north-facing classrooms at the Jordan University of Science and Technology (JUST). The data from this research were obtained using computer simulations and real measurements. The combination of the office window and the south-facing anidolic ceiling provided about 62% of the light needed for the classrooms, and reduced the energy consumption required for lighting and heating by 16.3%. According to Yener [77], classroom lighting should be adequate for activities such as reading and writing on the blackboard and at desks. Kruger and Dorigo [78] found that each country has its own classroom lighting standards, but they all fall within the 300–500 lx range. Many are based on guidelines published by the Illuminating Engineering Society of North America (IESNA) and the European Standards (CEN).

Currently, the tools that are available to evaluate green buildings include the evaluation of Indoor Environmental Quality (IEQ) and obtaining the health of the occupants, and one of the elements that can be evaluated is visual comfort. Adaptive re-use is one of the well-known strategies to improve the sustainability of existing buildings in order to reduce material, transport, and energy consumption, as well as pollution levels [79]. Changes in building function have degraded the level of many buildings' IEQs, including their indoor lighting performance. The performance of indoor lighting is generally measured by the lighting level (E), daylight factor (DF), and the uniformity ratio. The illuminance level may vary in each room, with their different functions.

DF = Ei/Eo × 100(%), where Ei = indoor illuminance, Eo = outdoor illuminance (varies from 20–130 klx), and DF = daylight factor.

Based on previous research, Susan and Prihatmanti (2016) [80] stated that lighting in educational institutions is a critical factor, because poor lighting is not only detrimental to the visual comfort of the occupants, but could also lead to eye fatigue.
