Glare
Glare occurs when lighting conditions impair vision or are perceived as unpleasant. This can be caused, for example, by a high luminance of a light source or a significant difference in luminance within the field of view.
Glare therefore does not depend solely on the total amount of light produced by a headlamp. Key factors include the light distribution, the position of the light source within the field of view and the ambient lighting conditions.
Physiological and psychological glare
Broadly speaking, two effects can be distinguished.
- Physiological glare impairs the ability to recognise objects or details. Light from a glare source is scattered within the eye and can thereby reduce the perceived contrast. An object may therefore be more difficult to recognise, even though it is itself sufficiently illuminated.
- Psychological glare, on the other hand, causes an unpleasant or disturbing sensation without necessarily resulting in a measurable impairment of visual ability.
Both forms can occur independently of one another. The perception of glare also depends on the prevailing visual conditions and, in the case of psychological glare, on individual perception. The CIE points out, particularly with regard to vehicle and street lighting, that the assessment of psychological glare is complex.
Glare from vehicle lighting
In vehicle lighting, the limitation of glare is particularly important in the case of low beam. Their beam pattern has a defined cut-off line. This limits the light output to areas where it could impair oncoming or leading road users.
With high beam headlights, this limitation does not exist to the same extent. It can therefore have a significantly greater dazzling effect on other road users and must only be used under appropriate conditions.
Incorrect adjustment or fitting of a headlamp can also result in light being emitted in undesirable directions, thereby increasing glare.
Glare from work lights
Glare is also a relevant issue with work lights. An unsuitable position or alignment can result in the driver or people in the work area looking directly into a high luminance.
Furthermore, highly reflective surfaces can contribute to glare. When selecting and fitting a worklight, therefore, in addition to luminous flux and illuminance, the light distribution pattern, the mounting position and the lines of sight of the people involved must also be taken into account.