The CdS is a light sensitive resistor offering a range of 160 ohm to 700k sensitivity.
This is a simple to use light sensor that outputs an analog value from 0 to 5V. With exposure to daylight, this sensor will output 5V.
The Parallax ColorPAL is a miniature color and light sensor which uses an RGB LED to detect and generate light for color sensing.
When the QTI sensor is over a dark surface, the reflectivity is very low; when the QTI is over a light surface, the reflectivity is very high and will cause a different reading from the sensor.
The Precision Light Sensor measures human perceptible light level in lux.
This module can be controlled with external circuit to quantify and record the brightness of ambient environment, thus providing a hardware infrastructure for intelligent controlling system that varies according to the ambient brightness.
We've had an eye on this Vishay sensor for a while - smart, tidy, and small. Thanks to SparkFun for breaking it out so you can use this to measure ambient light, and physical proximity in a single sensor!