Adafruit GA1A12S202 Log-scale Analog Light Sensor

This sensor has great sensitivity in low light and is almost impossible to max out making it perfect for almost any application! The biggest improvement this board offers over plain photocells is a true log-lin relationship with light levels. Most light sensors have a linear relationship with light levels, which means that they're not very sensitive to changes in darkened areas and 'max' out very easily when there's a lot of light. Sometimes you can tweak a resistor to make them better in dark or bright light but its hard to get good performance at both ends.

• Like a CdS photo-cell, the sensor does not require a microcontroller, the analog voltage output increases with the amount of light shining on the sensor face.
• Logarithmic over a large dynamic range of 3 to 55,000 Lux, so it has a lot of sensitivity at low light levels but is also nearly impossible to "max out"
• Use it indoors or outdoors without changing code or calibration
• Since the sensor is fabricated on a chip, there are also fewer manufacturing variations, so you won't have to calibrate the sensor from one board to another.
• Power with 2.3-6V
• Onboard 68K load resistor for max 3V analog output

Using the sensor is easy as pie: connect the Vin to 2.3-6VDC, Gnd to ground and measure the analog output on OUT. It will range up to 3V (at extremely bright outdoor sunlight). On an Arduino, just use analogRead() with the OUT pin connected to an analog pin. For more information including graphs, power consumption, etc check out the datasheet. On this breakout we placed a 68K? resistor from OUT to ground to turn the current into a voltage.