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Selenium photocell exposure meter


A pile of exposure meters

I have tried to concentrate on collecting only cameras but as a bonus I have received some separate exposure meters.They all are match needle type with a selenium light sensor. Selenium exposure meter don´t need a battery. Selenium cell produces electrcity when exposed to light. That is the idea of a selenium exposure meter.

I made some inquiries using books and know-it-all Google and got these answers:


Selenium : Symbol Se A nonmetallic element, red in powder form, black in vitreous form, and metallic gray in crystalline form, resembling sulfur and obtained primarily as a byproduct of electrolytic copper refining. It is widely used in rectifiers, as a semiconductor, and in xerography. Its photovoltaic and photoconductive actions make it useful in photocells, photographic exposure meters, and solar cells. Atomic number 34; atomic weight 78.96; melting point (of gray selenium) 217°C; boiling point (gray) 684.9°C; specific gravity (gray) 4.79; (vitreous) 4.28; valence 2, 4, or 6.s discovered by the Berzelius in 1817 ( Berzelius , Jöns (1779-1848), Swedish researcher who is known as the father of chemistry.) , and in 1873 Smith found that the resistivity of selenium was a function of the intensity of the illumination falling on the surface of the material. What is then a photocell? It is a photoelectric cell that uses a strip of selenium. Selenium photocells are commonly used in photographic-exposure meters, burglar alarms, etc.   ... Exposure meter: The photographer's tool for measuring light. A properly-exposed film will produce an image that correctly reproduces the subject in true-to-life tones and colors. The etymological background of the noun Selenium comes from the Greek word selas which means brightnes, light.

What is Light?

Anywhere around us on the the earth and also in the space there can be found electromagnetic radiation. The source of the radiation could be a star or something which is related to the birth of the Universe, then we are speaking about the Background Radiation. Radars, radio transmitters a burning candle or even the human brains are the sources of electromagnetic radiation.

Visible light waves are the only electromagnetic waves we can see. The wavelengths of the light we can see range from 400 to 700 billionths of a meter. But the full range of wavelengths included in the definition of electromagnetic radiation extends from one billionth of a meter, as in gamma rays, to centimeters and meters, as in radio waves. Light is one small part of the spectrum. We see these waves as the colors of the rainbow. Each color has a different wavelength. Red has the longest wavelength and violet has the shortest wavelength. When all the waves are seen together, they make white light. When white light shines through a prism or through water vapor like in a rainbow, the white light is broken apart into the colors of the visible light spectrum.

How do we "see" using Visible Light?

Cones in our eyes are receivers for these tiny visible light waves. The Sun is a natural source for visible light waves and our eyes see the reflection of this sunlight off the objects around us.The color of an object that we see is the color of light reflected. If the color of the object is white it means that all the wavelengths of the visible light are reflected. If it is black it absorbs all the light.

©2005 Reijo Lauro