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Light Sensors

Cameras@ LED@ Wearables@ Infra-Red I/O@ Fiber optics

Richard Ottoson says:

...a quick rule of thumb about opto's:

These times assume a "reasonable" resistor value. There are amplified optocouplers that are in the 100ns range as well.

Application notes on photodiodes ( A Primer on Photodiode Technology has some simple circuits for photodiodes, and tons of nit-picky detail on how they work. Offline as of 2009-06-13 -- has it moved elsewhere?  Perhaps to

Brian Kraut says:

Go to your local disco and theatrical lighting supply store and ask for for a gell sample book. Voila, about 100 different color plastic filters in 1 X 3" size. Some of them even have spectral response graphs for each sheet.

James Newton Says: " For optical interruption sensors, don't forget your standard super low cost "mechanical" mouse! " +

Phototransistors +


Dark Current
A small value current that flows in a photodiode while reversed biased, due to thermal generation of carriers and surface leakage with no incident light (also called leakage current).
Range: a few pA to 10 m A
Photo Current
Flow of current generated by a photodiode in response to an incident optical power. The absorbed photons generate free charge carriers that are collected within the
Photo Voltaic Mode
Unbiased mode of operation of a photodiode, preferred in low frequency (up to 350 MHz) as well as ultra low light level applications.
Photo Conductive Mode
Reverse biased mode of operation of a photodiode, in which lower capacitance and faster rise time are obtained. Generates more noise (dark current).
Shot Noise
Noise related to the statistical fluctuation in both the photocurrent and the dark current. It is the dominant noise in the photoconductive mode.
Shunt Resistance
Defined as the current flow in the dark of a photodiode when reverse biased at 10mV. More current flow reduces the effect of noise.
Thermal Noise
All devices have a thermal (or Johnson) noise associated with them, due to thermal generation of carriers
Noise Equivalent Power
Optical power necessary to create a photocurrent equal to the noise, to obtain a signal-to-noise ratio of 1. It depends on the noise current and the responsivity.
Responsivity (or Sensitivity)
The ratio of output current (in Amperes) to input light power (in Watts). It is a constant in the dynamic range, at a given wavelength.
A drift in output for a detector submitted to a constant input optical power for a long period of time.

See also:

file: /Techref/io/sensor/light.htm, 9KB, , updated: 2011/9/6 12:34, local time: 2018/7/16 09:54,

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