Sometimes glare is purely subjective; what you find annoying may be unbearable to some people while others may describe the same condition as sparkling. A glare condition may be hard to describe and is virtually impossible to quantify or measure.
The essence of most glare is the contrast in levels of light to which our eyes must adjust.
Contrast is the difference between surface or light sources of different “objective brightness.” A car headlight that causes glare would hardly be noticeable during the day. The “luminance” or the amount of light emitted from the headlight hasn’t changed but the contrast between the headlight and the surrounding light levels have changed. What remains constant is the headlight’s “objective brightness.”
Types of Glare
It is considered that there are two general types of glare: disablement and discomfort. The difference between the day and night situation is that the background luminance changes. If there is too great a difference, the luminance is called glare.
Disablement glare can make it dangerously difficult to see, such as when an approaching car’s headlights are on high beam and physically prevent you from seeing other objects.
Discomfort glare is just what it sounds like, uncomfortable and fatiguing, making viewing possible but still possible. Over prolonged periods the strain can cause fatigue and headaches. This type of glare is often present in the home resulting in discomfort and reduced visibility.
Sources of Glare
In the home environment, glare comes from two main sources. The first is the light from interior fixtures that is reflected from surfaces or TV/computer screens. An effective solution may be as simple as rearranging the room to a more favorable orientation. The second is caused by the extreme difference in light levels between sunlight transmitted through exterior windows and the light within the room. Solutions for this condition should consider factors such as the use of daylight in lighting and the need to retain vision through the glass.
Glare Reduction Window Film
Discomfort glare from windows can be greatly reduced by applying a window film that reduces visible light transmission to an appropriate level but maintains vision through the glass.
Disablement glares are best managed with translucent window films that may maintain a higher level of light transmitted into the space but preclude vision through the glass, dark blinds or shutters.
These solutions should be matched with other pertinent characteristics of the home; professional specifiers can help to achieve a good balance between aesthetics, costs and effective relief from glare.