Glare (vision)

Glare referred triggered on high brightness optical or visual disturbance that leads to the excessive demands of the visual system. Transfer and simplified also be sources of interference, leading to over-exposure optical technical devices, called glare.

Basics

Meeting too many photons in too short a time to a receptor, it is oversaturated. The light input is measured as the brightness per unit area multiplied by time duration. Thus, the illuminance ( lm / m ) point light sources can be represented as a surface or sum of point- luminance ( in cd / m²) scale sources. Depending on whether the supersaturation occurs only in a small area or for the entire field, it is called local or total glare. The local glare comes mostly by differences in luminance of the environment into existence ( relative brightness ), while the total glare is caused by an overall high incidence ( absolute magnitude ).

Glare is commonly referred to as "white" displayed because an increasing light intensity in the relevant for the measurement of light perception or model of additive color mixture flows into the white color impression - and of photographs depicting positive also white on the. But glare can also be caused by monochromatic light.

Disturbance of visual function

In the glare play the respective limits of the capacity for adaptation of the eye to changes in luminance conditions - by oculomotor reactions like Lidspiel and pupil game for the optical apparatus and by retinal adaptation of receptors as neurons of the visual system - and the duration and time course of this adaptation to light an essential role ( light blindness).

The healthy eye is able to make to adapt to the changing luminance around moonless night up to blazing sunshine and in the broad freedom of 1:1012; it needs for small fluctuations only fractions of seconds and from one extreme to another usually under 30 minutes, faster than the dawn. Apart from eyelid closure and width of the palpebral fissure ciliated four different processes or factors are responsible for:

Emergence of the glare

The visual system adapts to optimizing a given environment luminance. Often, however, the surrounding luminance not homogeneous and includes differences, sometimes significant. For example, there is a bright ( disturbing ) light source in the visual field, a light curtain can formally be placed over large areas of the retina inside the eye produced by scattered light from the interference light source. The eye adapted in this case to a higher luminance level higher than the surrounding luminance would actually be appropriate, as a result of the intraocular luminous veil. This veiling luminance can already affect the function of vision when they account for only about 1 to 2 percent of those luminance, as it exists in each case at the location of the visual field to which the current visual information just by reference.

The generation of stray light inside the eye is often due to scattering centers, which are located in different numbers in the refractive media of the eye, whether in the cornea, lens or vitreous. These scattering centers can be for example opacifying inclusions or transparent areas with other refractive index, which now distract the light diffusely and contribute to the mentioned veiling luminance. In particular, since the transparency of the eye lens is highly dependent on age, and the glare of a comparable interference light source may vary depending on age.

Forms of glare

If there is a measurable impairment of vision, one speaks of physiological glare; is the glare given subjectively, but impaired visual performance by external measurements undetectable, a discomfort glare is assumed.

Are the luminances of the environment such that the visual system is no longer able to adapt even to this level, this form of blending referred to as absolute glare, in other cases, as an adaptation transition. Addition, a distinction between a direct glare which is caused by a light source itself, or indirect glare which is caused by the ghost image of a light source.

In summary it can be stated that an absolute glare is present when the eye because of interference light source can not sufficiently adapt to the luminance of the rest of the visual field and so the visual recognition in the rest of the visual field is limited because of the lack of adaptation. For a visual system so that the limit of its adaptability is achieved in differences in luminance intensity within the field of view.

Glare of technical devices

Analogous to the eye may dazzle with technical optical systems occur. In photography can be a glare or over-exposure by controlling the exposure or Aperture settings - which corresponds to the opening width and opening time in about pupillomotorischen adaptation of the eye - usually largely control ( Fade Out ).