Photoswitch

A photoswitch, or photo-electric switch, is a sensor that detects the presence in or change of light. A popular example is that of azobenzene. Photoswitches are one type of molecular machines, a class of molecules that can be switched between at least two distinct thermodinamically stable forms by the application of an external stimulus. Development of such devices is crucial in the framework of the field of nanotechnology: nowadays photoswitches are used in a variety of places from scientific applications to residential light timers.

A photoswitch molecule is a chemical that is sensitive in some way to light, e.g. able to turn on retina cells when exposed to light,. Some examples include AAQ, DENAQ, photochromic compounds, azobenzenes, spiropyrans, diarylethenes, fulgides, overcrowded alkenes.

A photo-electric cell is connected to a circuit that measures how much electricity the cell produces and according to the setting of minimum and maximum lux level, the circuit decides and gives the output.

The issue of the photoswitch that the reflecting efficiency of the reflecting member may be drastically lowered due to dewing and clouding of the reflecting surface due to a change in the ambient temperature. The dew on the reflecting surface causes a random reflection. In order to avoid the clouding of the reflecting surface, it has been proposed to apply silicon or the like to the surface of the reflecting member. This countermeasure, however, cannot prevent condensing of dew onto the lower part of the reflecting surface. Thus, there are many problems in the prior art.

...
Wikipedia