What is glare?
Due to the unsuitable brightness distribution or brightness range, or the existence of extreme brightness contrast, visual phenomena that cause uncomfortable feelings or lower the ability to observe details or targets are collectively called glare.
If the human eye is exposed to glare, it feels irritated and nervous, and working under such conditions for a long time produces boredom, impatience and fatigue, which has a great impact on people’s work and life. Glare can be classified as uncomfortable glare and disabling glare according to its degree of visual impact.
People feel only uncomfortable, which can cause distracting effects, but it does not necessarily reduce the visibility of visual objects in a short time. Such glare is called uncomfortable glare.
As the position of the light source close to the line of sight, the edges of the retinal image are blurred, thus hindering the observation of nearby objects, reducing the visibility of visual objects and, if it is suppressed laterally, making the visibility of these objects worse, such a glare is disabling glare.
The CIE (Council on International Illumination) has developed the concept of anti-glare for luminaires and has incorporated the UGR (Unified Glare Resistance) concept into the UGR. (Glare Rating) as an indicator for evaluating uncomfortable glare in indoor lighting environments.
With the development of LED chip technology, LED luminaires are getting brighter and brighter, and uncomfortable glare is getting worse and worse. Therefore, in 2014, the European Union made the UGR limit value as a mandatory standard for luminaires, instead of just as a reference as before.
Below box lists the UGR limits for several types of places specified by CIE:
Generally speaking, “UGR<19” only meets the basic glare requirements in schools and office spaces. In fact, in actual use, customers will still prefer UGR smaller lamps. If you look at the following table of UGR and uncomfortable glare level, you will have a better understanding: UGR=19, in fact It is a representation of discomfort. The smaller the UGR value in the work and study place, the better.
Glare is divided into four categories according to the mechanism of formation: direct glare, indirect glare, reflected glare and contrast glare.
Direct glare is the glare produced by the presence of a luminous body in the direction of the object being observed or in the direction of the approaching line of sight.
In the built environment, the sunlight through the glass, the luminous ceiling and the light source in the lamps, etc., when these light sources are too bright, it will produce direct glare.
A high-brightness light source in the field of view, but it is not in the direction of the observation object. At this time, the glare it causes is indirect glare.
Glare caused by reflections, especially glare caused by reflections near the line of sight. According to the number of reflections and the mechanism of forming glare, reflected glare can be divided into primary reflection glare, secondary reflection glare and light curtain reflection.
The primary reflected light refers to the specular reflection phenomenon or the diffuse specular reflection phenomenon caused by the strong light projected onto the object being viewed due to the reflection of the surface gloss of the target object.
For example, when a mirror is hung on the wall opposite the window, when sunlight enters from the window, we observe a light spot in the frame. This light spot is actually an image of a side window.
Secondary reflected light is when the brightness of the human body or other objects is higher than the brightness of the surface of the object being viewed, and their reflected image just enters the person’s line of sight. Or the reflected image of the object, making it impossible to see the target object clearly. For example, when you stand in a glass showcase and want to see the display, you see yourself instead. This phenomenon is secondary reflection glare.
A light curtain reflection is a specular reflection of a visual object that reduces the contrast of the visual object to such an extent that it is difficult to see some or all of the details of the object. For example, when light shines on the surface of a document printed on smooth paper and most of the light is reflected into the viewer’s eyes, if the article The words are dark & shiny and also reflect into the viewer’s eyes, which results in a light curtain reflection, making it difficult for the viewer to see the text.
The reason why people feel uncomfortable is not only the light stimulation, but also the brightness of the environment.
If the difference between ambient brightness and the brightness of the light source, the contrast in brightness will be great and the more likely it is that contrast glare will form.
Thinnk about that, when a street lamp is lit, pedestrians will not notice its existence during the day; But at night, people will feel that the street lamp is dazzling. Because the background brightness of the night is very low, and the street lights appear very bright, forming a strong contrast glare.
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