**1. Introduction**

Globally, an increasing number of people are aging; consequently, the quality of life of elderly persons has become the focus of the international community. It is crucial to provide a comfortable lighting environment for elderly persons. Due to visual decline [1], special consideration should be given to the lighting design of their living spaces. Reading is among the most popular leisure activities among elderly persons [2–5]. However, with age, the ciliary muscle loses its ability to contract and the pupil size decreases, resulting in presbyopia [6]. There is insufficient light intake for narrow pupils. Hence, elderly persons often need higher illumination to make up for the decline in visual ability. Studies have shown that illumination considerably influences the reading ability of elderly persons with low vision [7]. As the world's population ages, many countries and institutions have studied the illumination standard of reading for elderly persons and recommended specific values and ranges. However, lighting design standards in different countries do not have an agreed illumination value required for reading. The Architectural Lighting Design Standard of China [8] stipulates that, typically, reading lighting in the bedroom should be 300 lx. American National Standards Institute (ANSI) lighting standards [9] stipulate that reading lighting in the bedroom is 750 lx. The Lighting Handbook of Japan [10] stipulates

**Citation:** Fu, Y.; Wu, Y.; Gao, W.; Hui, R. The Effect of Daylight Illumination in Nursing Buildings on Reading Comfort of Elderly Persons. *Buildings* **2022**, *12*, 214. https:// doi.org/10.3390/buildings12020214

Academic Editor: Alessandro Cannavale

Received: 30 December 2021 Accepted: 8 February 2022 Published: 15 February 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

that reading lighting in the bedroom is 600–1500 lx. Some scholars have conducted studies on the illumination preferred by seniors in terms of reading. Robert G. Davis conducted an experiment on the visual preference of elderly persons when reading under 1076, 107.6, and 10.76 illuminations. Results indicate that the favored illumination of elders was 1076 lx [11]. Zhang and Ma investigated the visual executive power and subjective comfort of elderly persons when reading under 50, 300, and 1000 lx. The results showed that elderly persons had the best visual executive power and relatively good subjective comfort when reading under 1000 lx [12]. The standards and research listed above were set or carried out under the assumption of artificial lighting. According to the living habits of the elderly persons, it is normal for them to read in daylight in front of windows. In the context of carbon peaking and carbon neutrality, it is also encouraged to make full use of daylight in daily activities. However, no detailed regulations apply to daylight illumination in the lighting design standards according to indoor activities of elderly persons in China, Japan, or the United States.

Illumination is a common parameter for evaluating the quality of daylight environment, and lighting evaluation methods such as DF, DA, and UDI all use illumination as the basic parameter. Illumination has an important supporting role for human visual function, and is not only the most important photometric indicator for elderly persons to complete reading tasks, but also one of the important indicators for evaluating the comfort and health associated with the lighting environment. Furthermore, elderly persons, as a special social group, have a certain dependence on daylight [13]. Physiologically, daylight can regulate the secretion of melatonin in their bodies and promote the absorption of calcium ions. Psychologically, daylight can reduce the risk of depression in elderly persons. Although they have different needs for daylight, they are highly satisfied with activities performed in a daylight environment [14]. As such, it is of great significance to focus on the impact of daylight illumination on the reading behavior of elderly persons in nursing buildings.

The main purpose of this study was to investigate daylight illumination of comfortable reading for elderly persons. "Comfort" is a state of relaxation and peace without physiological pressure, which is related to the overall state of a person. The full range of factors, both mental and physical, can be described as being involved in the state. Traditionally, subjective questionnaire surveys are commonly used in comfort-related research, such as human perceived comfort experience and comfort evaluation. This paper refers to the methods used in international research on emotions. Based on the view that "comfort" includes not only physical sensations, but also psychological factors [15], the combination of a physiological index measurement and a subjective questionnaire survey was used to analyze state arousal level and visual comfort in the reading of elderly persons. The effect of different levels of daylight illumination on reading by elderly persons was then explored.

#### **2. Materials and Methods**

#### *2.1. Research Subjects*

Elderly persons living in senior care institutions were the research subjects of this study. The enrolled subjects met the following requirements: self-care elderly people aged 60–89, graduated from primary school or above, with normal naked or corrected vision, no color blindness, cognitive impairment, or Alzheimer's disease, and reading behavior at least twice a week. A total of 30 seniors were enrolled, 15 men and 15 women.

#### *2.2. Reading Materials*

To reduce the impact of different reading materials, fonts, and other factors on the physiology and psychology of elderly persons, the length of each reading activity was controlled; also, the reading material was provided by our research group. The newspaper was selected as the experimental reading material (Figure 1). The background color of the newspaper was light gray and white. The font color was black, and font size was the 12 pt. for Han Chinese characters. Eight paragraphs from eight issues of the newspaper were randomly selected. The layout of each paragraph was the same with 100 words each. The reading time of each paragraph was controlled at approximately 5 min, and each paragraph was in the same position of the newspaper. The content of the material was serial articles. Simple and understandable emotional stories were selected to eliminate personal preferences of elderly persons and reduce the impact of article content on their cognitive and emotional states.

**Figure 1.** Reading materials.

#### *2.3. Daylight Illumination Measurement*

This study was based on the residential building of an elderly care institution in Dongling District, Shenyang, China. The building was established in 2014, with four floors and 12 households on each floor (Figure 2). All dormitories are single rooms, with a size of 3.6 × 6 m. These dorms include bedrooms, a leisure area, and independent bathrooms. The walls and ceilings in the room are painted white, and the floor is made of brown wood. The window in the room has a size of 2 × 1.8 m and is a height of 1 m from the ground, and faces south.

**Figure 2.** Floor orientation and room layout.

The elderly persons read experimental materials on the desk under the window. The desk is 0.75 m high, and the chair is 0.42 m high. After a survey of 30 elderly persons, their one-day activities were summarized in Table 1, and experimental time was finally determined. The illumination was measured between 8:00 and 10:00 every morning. Combined with the Architectural Lighting Design Standard of China, the illumination range of the experiment was set as 300–1000 lx. Prior to the start of the experiment, the elderly persons were free to change the illumination using the curtains. A TES-1330A illumination meter (TES Electrical Electronic Corp.) was used to measure the illumination before the elderly persons started reading. Electrodermal activity (EDA) data were received in real time using a laptop placed on the table at the rear left of the subject (Figure 3).


**Table 1.** The general situation of nursing homes.

Types of activity: A. Reading books and newspapers; B. Getting up; C. Using computer; D. Watching TV; E. Doing housework; F. Fitness; G. Walking; H. Playing mahjong; I. Raising flowers; J. Play chess; K. Sleeping; L. Eating; M. Chatting; N. Dancing P. Others.

**Figure 3.** Experimental area plan.

The final illumination value was determined using the mean value of the illumination at the midpoint of each side of the reading material and the intersection of the diagonal (Figure 4). To reduce the fluctuation in daylight illumination, reading material with fewer words was first chosen in order to minimize the reading duration. Based on the experience during the pre-experiment, the elderly persons are not sensitive to changes in illumination within 50 lx. Thus, when the experiment was carried out, the illumination meter was placed close to the top of the reading material, and data that did not change beyond 50 lx throughout were adopted. A staff member stood at the left rear of the elderly persons and observed the illuminance meter's value on the table throughout the process to control the illumination change during the experiment (Figure 3) in order to avoid the problem of glare or uneven illumination during the experiment, which may have caused discomfort to the elderly persons. Before the experiment, the elderly persons could slightly adjust the position of the curtain, chair, and reading materials according to the actual situation (Figure 5). At the end of the experiment, elderly persons were asked if they encountered glare or excessive fluctuations in their visual field brightness. Data collected when this occurred were eliminated. The measurements were performed over 20 weeks from September 2017 to March 2018, and 217 valid data points were obtained.

**Figure 4.** The selected points of the illumination value.

**Figure 5.** Adjustable position.

*2.4. Visual Comfort Level Measurement*

#### 2.4.1. Measurement of Skin Conductance

When an individual engages in cognitive activities or is exposed to particular emotional stimuli, areas of the brain such as the anterior cingulate gyrus and the amygdala act, resulting in a sympathetic nervous system reaction [16]. The more excited the sympathetic nervous system becomes, the more stimulated the sweat glands become. In addition, the sweat glands secrete sweat to the skin surface through pores in the skin. When a balance between positive and negative ions in the secretion occurs, the skin conductance (SC) changes. Changes in SC thus indicate the activity level of specific areas of the brain during reading tasks, notably crucial cognitive and emotional activities. According to research, the neural systems of emotion and cognition are closely interwoven, and both positive and negative emotions play a role in learning and remembering [17]. Thus, it can be seen that the shift in SC indicates the state arousal level of the elderly persons during reading. However, it is possible that a well-lit environment facilitates the arousal or that the arousal compensates for the annoyance produced by a poor light environment. This was investigated further with the subjective questionnaire. The mean of the time-domain characteristics of the SC can reflect the average level of electrodermal activity in the statistical period [18]. The

greater the absolute value of the mean change rate in different periods, the higher the state arousal degree.

An electrodermal activity (EDA) wireless physiological sensor (KingFar International Inc. Beijing, China) was used to collect and monitor the data of the SC indicators. Data storage and analysis were performed with a human–machine environment synchronization experimental platform (Ergo LAB). During reading, the elderly persons needed to wear the EDA wireless physiological sensor on the palm via an electrode so that the original physiological signal could be collected and transmitted to the Ergo LAB experimental platform in real time (Figure 6). The experimental platform has built-in filtering methods such as Smooth, Guass, and Hann, which can extract SC index data from the collected original signal and analyze the mean of SC time-domain characteristics in the corresponding time window.

**Figure 6.** Instruments. (**a**) Human–machine environment synchronization experiment platform. (**b**) EDA modules. (**c**) Physiological sensing kit. (**d**) Wearing instruments.

#### 2.4.2. Subjective Questionnaire

This research established two evaluation methods: a subjective comfort questionnaire and electrodermal activity measurement. The questionnaire was designed for the subjective visual comfort of elderly persons when reading at different illumination levels. The question was "What is your visual comfort level when reading at this illumination level?". The 5-point Likert scale method was adopted, in which five evaluation scales, from very uncomfortable to very comfortable, were used (Figure 7). There is no academic consensus on the concept of "visual comfort", and there are two widely used methods of evaluating visual comfort: One of them is the "no annoyance method", which states that no discomfort is considered comfortable. In other words, no physiological pain or irritation is considered to be visual comfort. Another is the "well-being method", which is based on subjective happiness and satisfaction [19]. In this study, "visual comfort" was defined as a state in which the reading task could be accomplished without physical or psychological stress by combining these two ways.


**Figure 7.** Subjective psychological evaluation scale.

At the end of reading, the persons enrolled in this study were asked whether they had fully seen and understood the reading materials. The data from the cases when they could not fully see and understand the reading materials were excluded. All respondents were informed of the purpose of the study and how the data would be used before filling out the questionnaire. According to the requirements of local legislation and institutions, this study did not require ethical review and approval. A total of 240 questionnaires were distributed, and 217 valid questionnaires were returned, with a recovery rate of 90%.

#### Q: What is your visual comfort level when reading at this illumination level?

#### *2.5. Experimental Process*

Before the experiment, the physiological signal baseline of the elderly persons was collected for 5 min in a daylight environment with approximately 300 lx illumination and uniform light. The mean value of the SC time-domain characteristics during this period was considered the baseline value. The collection site was on a chair next to a desk in the elderly person's own bedroom. The posture was a natural sitting posture, and the ambient illumination was adjusted using the curtains. The baseline only needed to be collected once, and there was no need to repeat it before every illumination.

After the baseline was determined, the participants could adjust their comfortable reading posture by themselves or adjust the illumination of the surrounding daylight by adjusting the curtains. After 3–5 min adjustment time, reading could start. The illumination value was randomly set in each experiment, in order to reduce the impact of the previous illumination value on the elderly persons; time was also left for them to make adjustments after each change in illumination. Throughout the reading process, the elderly persons wore physiological sensors. Ergo LAB human-machine experimental software marked the physiological data in real time at the beginning and end of reading. The recording stopped after the elderly persons finished their reading. Subsequently, the elderly persons began to complete the subjective questionnaire. The staff asked the elderly persons whether they experienced any discomfort such as glare during reading, and whether they fully saw and understood the content of the reading materials. The entire measurement process is illustrated in the figure below (Figure 8).

**Figure 8.** Experimental process.

#### **3. Results**

#### *3.1. Daylight Illumination Measurement Results*

A total of 217 illumination data points ranging from 300 to 1000 lx were used; this is the daylight illumination range that is acceptable for the elderly person to read. The questionnaire data and physiological data measured under different illumination levels were grouped according to the distribution of illumination data. The illumination difference corresponding to each group of data did not exceed 100 lx. Eight groups were recognized, i.e., "300 lx," "400 lx," "500 lx," "600 lx," "700 lx," "800 lx," "900 lx," and "1000 lx," with 25 to 30 valid data points under each group (Table 2).

**Table 2.** Illumination data summary.

