1 Introduction
Glare is a visual phenomenon in which the brightness distribution or brightness range in the field of view is unsuitable, or there is an extreme contrast, resulting in an uncomfortable feeling or a reduced ability to observe details or objects. According to the influence of glare on vision, it can be divided into discomfort glare and disability glare. In indoor lighting, there is generally no disability glare, and more uncomfortable glare occurs. In the Architectural Lighting Design Standards (GB50034-2004), glare is an important indicator of lighting quality and is evaluated using the Uniform Glare Index (URG).
The formation of glare can be thought of as the light from the glare source forms a bright light curtain on the retina superimposed on the image of the object being viewed. This light curtain reduces the contrast of the image and makes the target difficult to see.
From the perspective of visual ergonomics, glare can affect visual perception, which can cause irritability and uncomfortable mood, and affect people's mental health.
2 Unified glare index value of experimental light source
In order to evaluate the influence of glare on lighting comfort, glare evaluation experiments were carried out using 7 light sources of 5W/7W cool white LED, 5W/8W warm white LED and 25W/40W/60W incandescent lamp. These 7 kinds of light sources are all bulbs of the E27 lamp head, and the matte surface is frosted glass. First, the uniform glare index (UGR) of each light source was measured, and the results obtained are shown in Table 1.
Table 1 UGR values ​​of 7 kinds of glare sources
It can be seen from the calculated UGR values ​​that these kinds of light sources have slight glare, and the glare value of incandescent lamps is slightly lower than that of LED lamps, which are in the glare range that the human eye has a feeling.
3 Glare evaluation of different light sources in various lighting environments
This paper uses an eye chart to evaluate the effect of glare on the viewer's visual clarity. The experimental observers were 8 people, 6 males and 2 females, aged 25-40 years old. The corrected visual acuity reached 5.0, and the visual acuity scale 5.0 was at a height of 1.2 m, which was equal to the height of the normal sitting posture. The glare source is located 0.2m behind the center of the eye chart, and the height is 1.9m. The light from the glare source will not be directly on the eye chart. The observer is observed at 5.0 m in front of the eye chart, and the relative position is shown in Fig. 1.
Figure 1 Schematic diagram of the laboratory layout
In the experiment, only the ambient lighting source is turned on, so that the tester is familiar with the whole lighting environment. After 30 minutes, the tester can see the scale and accuracy of the eye chart; then let the tester rest for a period of time to relieve the eye fatigue and then turn on the glare source. After the tester is familiar with the glare environment, test the visual acuity and visual accuracy of the tester; finally turn off the glare light source, test the visual acuity and visual accuracy of the tester, and compare the visual acuity and visual accuracy with or without the glare light source. And ask about the psychological impact of the glare source on the tester.
The experiment adopted four kinds of background illumination sources, namely, grid fluorescent lamps, cool white LED lamps, warm white LED lamps and incandescent lamps. The following is a step-by-step analysis of the influence of glare sources on lighting comfort in each background lighting environment.
3.1 Glare of each light source in the environment of grille fluorescent lighting
The background illumination source uses the grille fluorescent lamp commonly used for office lighting, and the illumination value of the 0.75m work surface reaches 300lx. The fluorescent grille lamp is also the most common choice for office lighting. Experiments were carried out using the seven glare sources in Table 1. The experimental results of the glare sources are shown in Table 2.
Table 2 Glare test of 7 kinds of glare sources under the grid fluorescent lamp
It can be seen from the experimental results that before and after the glare source is turned on, the influence on the accuracy of the object is small, and it can reach more than 90%. In the experiment, it is found that the fatigue speed of the tester's eyes will be accelerated after the singular light source is turned on. If the illuminating light source is not turned on, it takes 3-4 minutes of focused observation to show a significant decrease in vision, and it takes only 2 minutes to turn on the glare source. Moreover, for the 7W and 8W LED light sources, the glare light source forms a distinct bright spot in the field of view, attracting the attention of the eye, and the long-term observation makes the eyes have a stinging feeling, which makes people blink frequently and the vision drops rapidly. The 45W and 60W matte incandescent lamps emit light that is softer, but creates halos that make the object look awkward and require more energy for concentration. After eye fatigue in the test, after a short break (gazing elsewhere or blinking, etc.), vision can be quickly restored.
3.2 Glare of each light source in a cool white LED lighting environment
The background illumination source is replaced with a cool white LED frosted bulb, which also makes the illumination value of the 0.75m work surface reach 300lx, and the color temperature of the light source used is 6500K. The position of the eye chart, the glare source and the observer are unchanged. The experimental results are shown in Table 3.
Table 3 Glare test of 7 kinds of glare sources under cold white LED bulbs
The cool white LED bulb is used as the background illumination. The visual accuracy under the glare source is similar to that in the fluorescent grid lighting environment. However, for the overall lighting environment, the general feeling of the tester is colder than that in the fluorescent light environment. Under the environment, the warm white LED forms a strong contrast with the background light. The glare light source is especially obvious when it is turned on. At the same time, the color difference will accelerate the eye fatigue, but it has little effect on the short-term visual accuracy. After the blink of an eye, it can recover faster. Scrub incandescent lamps tend to form light curtains or halos, blurring the gaze target.
3.3 Glare of each light source in warm white LED lighting environment
The background illumination source is replaced with a warm white LED frosted bulb, which also makes the illuminance value of the 0.75m work surface reach 300lx, the selected LED color temperature is 3000K, and the glare test of 7 kinds of glare sources is still performed. The test results are shown in Table 4.
Table 4 glare test of 7 kinds of glare light sources under warm white LED bulbs
Compared with the first two background lighting environments, the accuracy of the object has a certain decline. The overall lighting environment makes people feel warm and relaxed. There is no white light source on the lighting background (although it is the same illuminance value), especially after adding a low color temperature glare source, it will make the object blurred, and there is no clear under the cold white environment. . At the same time, in the warm white LED lighting background, the high-power cold white LED light source protrudes from the entire lighting background, giving a very glaring feeling and greatly reducing the accuracy of viewing things.
3.4 Glare of each light source in a frosted incandescent lighting environment
The final background lighting environment used for incandescent lamps, incandescent lamps have been used in the past two or three decades, but in the past decade or so, office lighting mainly uses fluorescent lighting, almost no incandescent lamps. Although incandescent lamps have gradually withdrawn from the office lighting market, in order to more fully and objectively evaluate the effects of glare in various lighting environments, it is necessary to experiment with incandescent lamps as background lighting. The experimental results are shown in Table 5.
Table 5 glare test of 7 kinds of glare sources under incandescent lamps
The use of 40W frosted incandescent lamps for background lighting also makes the desktop illumination reach 300lx. The tester generally reflected that in the incandescent lighting environment, the temperature of the laboratory rose and there was a feeling of fever.
Similar to warm white LED lighting, although the same illumination is achieved, incandescent lighting still feels not bright enough. After adding the glare source, the clarity and accuracy of the object are greatly reduced, especially after adding the cool white LED. The light source is in sharp contrast to the background illumination, which is glaring. When a warm white sleek light source is added, the sleek light source will be turned around, and the power is larger, and the range and extent of influence can be increased.
4 Summary
Comprehensive comparison of the experimental results of seven kinds of light sources, found that in the fluorescent light and cool white LED lighting environment, the impact of the glare source is small, with strong visual accuracy and clarity, in the incandescent and warm white LED lighting environment, The glare source is easy to form a light curtain and a halo, which blurs the entire field of view. At the same time, the cool white lighting environment has a cool feeling, easy to stay awake, good for efficient work; low color temperature makes people feel warm, easy to fatigue, not conducive to efficient work. When selecting an office lighting source, it is recommended to select a white light source (fluorescent or cool white LED) to form a better lighting environment and reduce the effects of glare.
The cool white glare source gives a glare, and the greater the power of the light source, the more obvious the feeling; the warm white glare source makes people feel guilty, especially in the same color background environment. Regardless of the cool white glare source or the warm white glare source, when the glare source is different from the background illumination environment, the glare source will protrude above the background, attracting the attention of the eye, especially the glare source with large brightness, which will make the eyes uncomfortable or even Stinging. When using the office lighting source, the same color source should be used. Unless there is a specific use, the light source of different colors should not be mixed to avoid obvious glare. At the same time, the power source should not be selected. The cold white glare source has high visual accuracy and good psychological feeling under the cold white background. The warm white glare light source is not low in the warm white background, but the feeling is ambiguous and fuzzy. Get up. From the perspective of glare, it is recommended that the office lighting select a low-intensity cool white light source as the illumination source, and fluorescent lamps and low-power cold white LED lamps are good choices.
Edit: Cedar
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