Glare is defined as the difficulty in vision caused by sources of Direct or Reflected Bright Light that may be Natural or Artificial. Glare occurs when the luminance of the task being done, to which the eye is adapted is lesser than the luminance of the source of Glare. The Bright Light from the Glare source, Constricts the pupil which results in low Field of Vision. Glare also depends on the clarity of the refractive media of the eye, the Intensity of the light, and the location of the Glare sources. Glare results in lower Visual acuity and lower Contrast Sensitivity. Reduction in the contrast happens when the bright light reflects within the eye.
The International Commission on Illumination (CIE) defines glare as : “Visual conditions in which there is excessive contrast or inappropriate distribution of light sources that disturbs the observer or limits the ability to distinguish details and objects.”
Glare can be of four types:
- Distracting Glare: This happens when the light travels from one optical medium to another . For instance, when light is reflected or scattered inside of a spectacle of the wearer. One cannot see your eyes due to reflection of light from anterior surface of the spectacle and you keep seeing the reflection of your own eyes from the posterior surface of the spectacle. This could be distracting or annoying sometimes to those who use spectacles regularly.
- Discomfort Glare: Discomfort glare results in an instinctive desire to look away from a bright light source or difficulty in seeing a task. The bright source of light in the field of vision leads to regular glare. Eye reacts either by squinting or constricting the pupil. The degree of discomfort glare depends on the size, luminance and number and position of glare sources. For instance when someone is working and he or she has a bright light that may be somewhere in his or her field of vision. That light can be a indirect glare to the eyes but could cause discomfort if it continues for long period of time. The dashboard light of a vehicle could also cause the discomfort glare to the driver.
- Disability Glare: In this type of Glare, The vision of the task that you are doing is lost due to a bright source of light. It doesn’t cause discomfort at all. When the vision is impaired due to such Glare, it is defined as DAZZLE. Disability Glare is also known as veiling Glare. The light that enters the eye scatters which can be caused by Cataracts or when a normal eye faces the bright sunlight directly. This Glare cause someone to see completely nothing till the light keeps entering the eye. This type of glare is mostly experience by drivers who are travel to the direction of the bright sun infront of them or sometimes the light from the oncoming vehicle. This is mostly experienced by elderly people with mild or moderate lens opacities.
- Blinding Glare: Light from sun sometimes gets reflected on water, sand, or snow and become polarized and form visual noise. The light then Haze and scatter (also called Rayleigh’s Effect) which in turn reduces the contrast. The Glare sometimes is so strong that it causes visual perception loss for few seconds.
How to Manage Glares?
- Using anti Reflective Coating Glasses to prevent the reflection of light caused by Lenses in a Spectacle.
- Photochromic Transitions lenses, which adapt their level of tint based on how much UV is present, can also help reduce the effects of glare.
- Using hat or caps can prevent discomfort Glare to some extent by preventing the light source from Field of Vision.
- Using polarized Glasses that cuts of light that is vibrating horizontally as the light beam gets reflected from a surface.
- Doing Cataract Surgery to prevent internal reflection of light due to Cataractous Lens.