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Technical environment
Technical environment
Global standard 220V-240V/50Hz-60Hz
Standard for USA/Canada 120V/60Hz, 277V/60Hz
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The ability of the eye to adjust to the luminances in the field of vision. Performed initially via the dilation or contraction of the pupils, though a far greater scope is achieved by altering the sensitivity of the retina´s receptor cells and by changing between vision with cone cells and vision with rod cells (see also Eye).

Adaptation

Typical illuminances E and luminances L under daylight and electric lighting.

Adaptation

Day and night

One of the most remarkable properties of the eye is its ability to adapt to different lighting conditions. We can perceive the world around us by moonlight or sunlight, although there is a difference of a factor of 100,000 in the illuminance. The extent of tasks the eye is capable of performing is extremely wide - a faintly glowing star in the night sky can be perceived, although it only produces an illuminance of 10-12 lux on the eye.

Luminance

Adaptation

This ability to adapt to the illuminance is only influenced to a very small extent by the pupil. Adaptation is performed to a large degree by the retina. The rod and cone system responds to different levels of light intensity. The rod system comes into effect in relation to night vision (scotopic vision), the cones allow us to see during the daytime (photopic vision) and both receptor systems are activated in the transition times of dawn and dusk (mesopic vision).
Although vision is therefore possible over an extremely wide area of luminances, there are clearly strict limits with regard to contrast perception in each individual lighting situation. The reason for this lies in the fact that the eye cannot cover the entire range of possible luminances at one and the same time. The eye adapts to cover one narrow range in which differentiated perception is possible. Objects that possess too high a luminance for a particular level of adaptation cause glare, that is to say, they appear to be extremely bright. Objects of low luminance, on the other hand, appear to be too dark.

Adaptation time

Adaptation

Adapting from dark to light situations occurs relatively rapidly, whereas adapting from light to darkness requires a considerably longer time. A good example of this is how bright we find it outside having come out of a dark cinema auditorium during the daytime or the transitory period of night blindness we experience when entering a very dark room. Both the fact that contrast in luminance can only be accommodated by the eye within a certain range and the fact that it takes time to adapt to a new level of lighting, or brightness, have an impact on lighting design. For that reason lighting design requires, for instance, the purposeful planning of different luminance levels within a space or deciding on the adaptation of lighting levels in adjacent spaces.

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Further topics on the human eye

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