Evaluation of lighting quality

The quality of lighting design is mainly measured by the quality of lighting. The following indicators of lighting quality should be comprehensively considered and properly dealt with in the design of lighting: illumination, luminance distribution, uniformity of illumination, shadow, glare, color of light, stability of illumination, etc.

(1) Illumination level

The solar energy environment should make it easy for the person to discern the details of the work he is doing, while eliminating or appropriately controlling factors that cause visual discomfort.

According to the International Council on Illumination (CIE), it takes about 1cd per square meter of light to just recognize the features of a face. This can be achieved in a normal lighting environment with a horizontal illuminance of around 20lx, which is considered to be the minimum illumination for any non-working room. Table 7.13 shows the recommended luminance ranges of the International Commission on Lighting Publication No.29/2 (TC-4.1) for various operational activities. The illuminance range consists of 3 consecutive illuminance levels. For a working room, the value in the middle represents the recommended illuminance to be used. The higher or lower values can be used when considering the reflection ratio, contrast, work needs and age of the staff of the job itself.

According to the current economic level and power supply capacity, and considering the specific situation of energy saving, China promulgated the “Architectural Lighting Design Standard” GB50034-2004 in 2004, which stipulates the standard value of illumination in various places for selection in design.

(2) Brightness distribution and inverse color ratio

The luminance distribution on each surface in the operating environment complements the illuminance design and is one of the important factors in determining the visibility of objects. The proper brightness distribution in the visual field is a necessary condition for comfortable vision. The brightness of the adjacent environment should be as low as possible as the brightness of the observed object. CIE recommends that if the brightness of the observed object is 3 times that of the adjacent environment, the visual clarity is better, that is, the reflection ratio between the adjacent environment and the observed object itself should be controlled within the range of 0.3~0.5.

In the working room, in order to reduce the brightness contrast between the lamp and its surroundings and the ceiling, especially when the embedded dark lamp is used, because the brightness on the ceiling comes from the indoor reflection for many times, the ceiling reflection ratio should be as high as possible (not less than 0.6), in order to avoid the ceiling is too dark, the ceiling illumination should not be less than 1/10 of the operating illumination. The REFLECTION RATIO OF THE WALL OR PARTITION IN THE working room HAD BETTER BE BETWEEN 50%~70%, and THE REFLECTION ratio of the floor should be between 20%~40%. Therefore below most circumstance, the requirement USES light color furniture AND LIGHT COLOR ground.

In addition, appropriately increasing the brightness contrast between the working object and the working background can improve the visual function more effectively and more economically than simply increasing the illuminance on the working surface.

(3) Uniformity of illumination

If there are surfaces with very different illuminance to each other in the working environment, it will cause visual discomfort. Accordingly, illuminance should be uniform on the working surface.

According to Chinese national standards, illumination uniformity can be measured by the ratio of the minimum illumination to the average illumination on a given working surface. The so-called minimum illumination is the minimum illumination of a point on the reference surface, while the average illumination is the average illumination of the whole reference surface.

CIE recommends that, under general lighting conditions, the ratio of minimum to average illumination in the work area should not be less than 0.8. The average illuminance of the whole area of the work room should not be less than 1/3 of the average illuminance of the work area generally, the average illuminance of the adjacent room should not exceed the change of 5:1 between each other, for example, the corridor outside the office where the illuminance is 100lx should have the illuminance of 20lx at least. However, for outdoor road lighting, the lighting uniformity can be allowed to be lower.

China’s Architectural Lighting Design Standard stipulates that the uniformity of general lighting in the working area should not be less than 0.7, and the illumination of the traffic area in the working room should not be less than 15 of the illumination of the working face.


(4) Shadow

Illumination in which the FLUX OF light on the ILLUMINATED surface comes from different directions is called diffuse illumination. Illumination diffusion can be effectively improved by increasing the reflection ratio of ceiling, scene and floor.

Directional light shining on objects (also known as directional illumination) will produce shadows and reflected light, at this time should be evaluated according to the specific circumstances of their good or bad. Shadows are harmful to vision when they are an obstacle to viewing; When the shape of the object can be expressed by the shadow (three-dimensional sense) and material sense, the appropriate shadow is beneficial to the vision.

(1) Diffuse light lighting should be used in situations where shadows are required to be avoided (such as drawing rooms with general lighting).

② In the design of industrial plant lighting, try to avoid the shadow formed by industrial equipment or other components.

(3) For lighting based on direct light, wide light distribution lamps can be used to evenly arrange, in order to obtain appropriate diffuse lighting.

④ The use of shadow “modeling” (the appearance of the object) to pay attention to the brightest part of the object and the darkest part of the brightness ratio, 3:1 is the most ideal. And the quality of the “modeling” effect is related to the intensity of light, direction and the direction of the observer’s line of sight.

When the surface OF THE object being ILLUMINATED is concave and convex, the effect of lighting can be used to highlight the small shadows it produces (such as the shadow on the surface of textiles), and to show the material sense of different textures. Under normal circumstances, this effect can be obtained by illuminating a directional light source from an oblique direction. In addition, for inspection lighting, building facade lighting and commercial lighting, we should pay attention to the effective use of shadows to achieve better visual and psychological effects.

(5) Glare

The presence of bright areas in the observer’s field of vision may cause the sensation of glare, make the person irritable (uncomfortable glare), and even reduce the observer’s visual ability (disabling glare). Since the factors controlling discomfort and disability glare are different, it is theoretically possible to ignore discomfort glare and pay attention to disability glare when it occurs simultaneously. However, this situation will not happen in practice. Because INDOOR LAMPS and lanterns have widely used diffuser and grille, direct incapacitate glare rarely happens, BECAUSE this IS IN indoor installation design, need to take into account uncomfortable glare only. However, in the outdoor high brightness lamps and lanterns often form a strong contrast to the gray sky, it will cause uncomfortable glare can also cause disability glare. According to Article 4.3.2 of China’s Architectural Lighting Design Standard (GB53004-2004), the uncomfortable glare in common rooms or places of public buildings and industrial buildings should be evaluated by unified glare value (UGR), and the maximum allowable value conforms to the provisions of Chapter 5 of the standard.

The direct discomfort glare (G) caused by an indoor lamp increases with the luminance (Ls) and its solid Angle to the observer (Ω), and decreases with the luminance background (Lb) and its relative position to the observer’s line of sight (P). Glare estimation systems have been developed based on the following formula:

But the difficulty is that the indices a, b, c and d all use different values. In the United States (IES-NA, 1993) this glare calculation was evolved as the “Probability of Visual Comfort (VCP)”. Some countries have taken a different approach by limiting the luminance of lamps to achieve a certain glare rating, which in turn depends on the average illumination value provided.

The International Lighting Commission has spent years seeking an internationally certified glare system for indoor discomfort, but it is now urgent to reach agreement on a “Uniform Glare rating (UGR)”, a G-type formula that, together with a “protection system”, comprises several sets of restricted luminance distributions. Although different indices are used in the glare formulation, the difference between the UGR glare value in the actual installation and the glare index value in the British system is very small. Both UGR and luminance limit systems classify glare into five levels, each representing a limit value for jobs with special visual requirements. Today, offices and factories in the United States use a lighting standard of 70 percent of the VCP, equivalent to a glare index of 19.

In the International Commission on Illumination’s description of the design procedure for traffic road lighting, the disabling glare is expressed as the “alarm increment (TI)”, which is the percentage increase in contrast required for objects on the road ahead to compensate for the disabling effect of direct light from the luminary.

(6) Color

The color characteristics of lamps are characterized by two different aspects: color table and color rendering.

The color table can be quantified by chromaticity coordinates, and the lamp near white is usually calibrated by correlation color temperature. Lights with low color temperatures appear warmer whites, while those with high color temperatures appear cooler whites. Table 7.14 shows the groupings of relevant color temperature values for indoor lighting adopted by the International Commission on Lighting (CIE, 1986b), but many people prefer to lower the starting point of the cool color group a few hundred degrees further in color temperature.

It has been agreed that the first set of lights is suitable for leisure places with less than 30lx illumination, the second set is suitable for mixing with daylight, and the third set is suitable only for indoor workplaces with high lighting levels.

The chromogenic property is expressed by the general chromogenic index. This is an important criterion to note for lighting Spaces that require accurate color judgments. Table 7.15 shows the five levels of color development index (CIE, 1986b) approved by the International Commission on Lighting, and shows the applicable places of each type of lamp.

The requirements of color rendering are especially strict in hospital wards and health centers. A special chromogenic index was used to determine the appropriate light for the ward, based on the color change of a sample that mimics the tone of human skin.

(7) directivity

Sometimes the visual work of a flat surface consists of details and backgrounds that are diffuse (with rough surfaces) SO that LIGHTING them FROM ANY Angle WILL not AFFECT their visibility. But in the real world, this phenomenon is extremely rare. Most materials exhibit mixed reflection properties, with a portion of the reflection being specular or specular, often independent of the rough surface reflection. When A real target is ILLUMINATED by a light fixture in the “exclusion zone”, some kind of light curtain reflection occurs and the contrast display factor is reduced, resulting in some reflective disabling glare.

If you want to represent a three-dimensional object, all the directions of the incident light are very important. The hardness of the object can be further determined by the degree of illumination on the curved object (model) and the shadows contained within its boundaries. The ratio of the illuminance vector to the illuminance scalar can be used to measure the degree of stereo sensation provided by the lighting system. Table 7.16 summarizes the subjective effects of different vector-scalar ratios. As can be seen from the table, the range of 1 to 2 is important for seeing a person’s appearance. Higher values are suitable for formal performance, a range of 2 to 3 is suitable for presentation, and higher values provide dramatic effect.