The sulfide (Tl2S) has been employed as the essential component in a highly sensitive photoelectric cell and the oxysulfide in an infrared-sensitive photocell (thallofide cell).
The photomultiplier tube is an enhanced version of the photocell, which was first used by astronomers to record data electronically.
In 1918 in Germany, the use of a modulated glow lamp in photographically recording sound and a photocell for reproduction were studied.
The dimming of automobile headlights, the setting of the diaphragm of a camera, and the correct exposure for colour prints may be accomplished automatically by connecting a photocell directly to the machine in question.
The pits are produced by a laser or by a stamping machine and are read by a low-power laser and a photocell that generates an electrical signal from the varying light reflected from the pattern of pits.
For sound reproduction, a beam of light is passed through the sound track onto a photocell connected, through an amplifier, to a loudspeaker.
The first of these utilized a heated pyramidal stylus, the motion of which was controlled by an electrical signal from a scanning photocell, to penetrate a plastic plate to a distance inversely proportional to the optical density of copy, thus burning out varying areas from the plate surface.
Often a transducer, an instrument that changes energy from one form into another (such as the photocell, thermocouple, or microphone) is used to transform a sample of the energy to be measured into electrical impulses that are more easily processed and stored.
When particles of smoke enter a portion of the chamber that is aligned with both the LED and the photocell, the particles diffuse or scatter the light ray so it can be "seen" by the photocell.
Some TTL systems divert the light from the lens to a photocell before it reaches the screen (e.g., by beam-splitting arrangements or the use of photocells behind a partly reflecting mirror), or they measure the light reflected from the film or from a specially structured first shutter blind at the beginning of, or during, the exposure.
The sound was reproduced during projection by directing a beam of light through the sound track onto a photocell, the response of which was electronically amplified.
