Lighting Tips | What is Glare?
The visual phenomenon that causes discomfort or reduces the ability to observe details or targets due to inappropriate brightness distribution or brightness range, or extreme brightness contrast, is collectively referred to as glare. If the human eye comes into contact with glare, it will feel stimulated and nervous. Working under such conditions for a long time will cause boredom, impatience, and fatigue, which will have a great impact on people’s production and life. Glare can be divided into discomfort glare and disability glare according to the degree of impact on vision.
(1) Uncomfortable glare
Visual discomfort only creates a distracting effect, but it does not necessarily reduce the visibility of visual objects in a short period of time. This type of glare is called uncomfortable glare.
(2) Disability glare
Due to the position of the light source close to the line of sight, the edges of the retinal image appear blurred, which hinders the observation of nearby objects and reduces the visibility of visual objects. If it is suppressed laterally, it will also make the visibility of these objects worse. Such glare is called disabling glare.
Glare can be divided into four categories based on its formation mechanism: direct glare, indirect glare, reflective glare, and contrast glare.
(1) Direct glare
Direct glare is the glare generated by luminous objects that exist in the direction of observation or close to the line of sight. In the built environment, when the sunlight passing through the glass, the luminous ceiling, and the light sources inside the lamps are too bright, direct glare will be generated.
(2) Indirect glare
Unlike direct glare, when there is a high brightness light source in the field of view but not in the direction of observing the object, the glare it causes is indirect glare.
(3) Reflective glare
Glare caused by reflection, especially when viewed close to the line of sight. According to the number of reflections and the mechanism of glare formation, reflection glare can be divided into primary reflection glare, secondary reflection glare, and light curtain reflection.
One reflection light refers to the phenomenon of specular reflection or diffuse specular reflection formed by the reflection of strong light rays projected onto the object being viewed, due to the surface gloss of the target object. For example, hanging a mirror on the wall opposite the window, when sunlight enters through the window, we observe the inside of the mirror frame
Something will produce a light spot, which is actually the image of the side window.
Secondary reflected light is when the brightness of the human body or other objects is higher than the surface brightness of the object being viewed, and their reflected images just enter the human line of sight. At this time, the human eye will see the reflected image of the person or object on the surface of the object, making it impossible to see the target object clearly. For example, when standing in a glass display cabinet and trying to see the display clearly, what you see is actually yourself, this phenomenon is called secondary reflection glare.
Light curtain reflection is the mirror reflection of visual objects, which reduces the contrast of visual objects, making it difficult to see some or all of the details of the object clearly. For example, when light shines on the surface of a document printed on smooth paper and most of the light reflects into the viewer’s eyes, if the text in the article is black and bright, and also reflects into the viewer’s eyes, a light curtain reflection will occur, making it difficult for the viewer to see the text clearly.
(4) Compare glare
The reason why people feel uncomfortable is not only due to light stimulation, but also greatly influenced by environmental brightness. The greater the difference between environmental brightness and light source brightness, the greater the brightness contrast, and the easier it is to form contrast glare. For example, a bright street lamp that pedestrians may not notice during the day; At night, pedestrians feel that street lights are very dazzling. Because the background brightness of the night is very low, while the street lights appear very bright, creating a strong contrast glare.
