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A LED is a long-lived light source, but certain mechanisms can cause slow loss of efficiency of the device or sudden failure. The wavelength of the light emitted is a function of the band gap of the semiconductor material used; materials such as gallium arsenide , and others , with various trace doping elements , are used to produce different ...
LEDs used in communications devices can have even faster response times. Focus: The solid package of the LED can be designed to focus its light. Incandescent and fluorescent sources often require an external reflector to collect light and direct it in a usable manner.
Response time 0.01 ms [10] to less than 1 μs, [11] but limited by phosphor decay time (around 5 ms) [12] 1–8 ms typical (according to manufacturer data), older units could be as slow as 35 ms [13] Typically less than 0.01 ms, as low as 2 μs, [10] [14] but limited by phosphor decay time (around 5 ms)
is the LED's forward voltage drop in volts when lit. and the LED's light frequency (which we perceive as color) increase with the band gap of the LED's materials. Consequently, ranges from around 1.7 to 2.0 volts for red LEDs to around 2.8 to 4.0 volts for violet LEDs.
Opto-isolator VTL2C1 with LED input and photoresistor output. Resistive opto-isolator (RO), also called photoresistive opto-isolator, vactrol (after a genericized trademark introduced by Vactec, Inc. in the 1960s), analog opto-isolator [notes 1] or lamp-coupled photocell, [1] is an optoelectronic device consisting of a source and detector of light, which are optically coupled and electrically ...
The combination of LED and photodiode is also used in many sensor systems to characterize different types of products based on their optical absorbance. Photodiodes are often used for accurate measurement of light intensity in science and industry. They generally have a more linear response than photoconductors.
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There are two luminous efficiency functions in common use. For everyday light levels, the photopic luminosity function best approximates the response of the human eye. For low light levels, the response of the human eye changes, and the scotopic curve applies. The photopic curve is the CIE standard curve used in the CIE 1931 color space.