Epoxy Resin Package Diameter 20mm CdS Photoresistor Light Sensor GM20539 For Sensor Applications


Electronics Characteristics

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Dimension unit:mm



Terminology

l Light Resistance :
Measured at 10 lux with standard light A (2854K-color temperature) and 2hr. preillumination at 400-600
lux prior testing.
lI Dark Resistance :
Measured at 10th seconds after closing 10 lux.
lII Gamma characteristic :
Under 10 lux and 100 lux and given by
γ = log(R10/R100) / log(100/10) = log(R10/R100)
R10, R100: resistance at 10 lux and 100 lux.
The tolerance of γ is ±0.1.
lV Pmax :
Max. power dissipation at ambient temperature of 25℃.At higher ambient temperature,the maximum
power permissible may be lowered.
V Vmax :
Max. voltage in darkness that may be applied to the device continuously.
Vl Spectral peak :
Spectral sensitivity of photoresistors depends on the wavelength of light they are exposed to and in
accordance with figure 'Spectral Response'. The tolerance of spectral peak is ±50nm.

Physical and Environmental Characteristics

Features

Quick Response
Reliable Performance
Epoxy or hermetical package
Good Characteristic of Spectrum


Application

Photoswitch
Photoelectric Control
Auto Flash for Camera
Electronic Toys, Industrial Control


Description

Photocells are sensors that allow you to detect light. They are small, inexpensive, low-power, easy to use and don't wear out. For that reason they often appear in toys, gadgets and appliances. They are often referred to as CdS cells (they are made of Cadmium-Sulfide), light-dependent resistors (LDR), and photoresistors.

Photocells are basically a resistor that changes its resistive value (in ohms Ω) depending on how much light is shining onto the squiggly face. They are very low cost, easy to get in many sizes and specifications, but are very innacurate. Each photocell sensor will act a little differently than the other, even if they are from the same batch. The variations can be really large, 50% or higher! For this reason, they shouldn't be used to try to determine precise light levels in lux or millicandela. Instead, you can expect to only be able to determine basic light changes.

For most light-sentsitive applications like "is it light or dark out", "is there something in front of the sensor (that would block light)", "is there something interrupting a laser beam" (break-beam sensors), or "which of multiple sensors has the most light hitting it", photocells can be a good choice !



Problems you may encounter with multiple sensors
If, when adding more sensors, you find that the readings are inconsistent, this indicates that the sensors are interfering with each other when switching the analog reading circuit from one pin to the other. You can fix this by doing two delayed readings and tossing out the first one.