VEML7700 Lux Sensor - I2C Light Sensor (ID:4262)
£4.99 ex VAT
Vishay has a lot of light sensors out there, and this is a nice simple lux sensor that's easy to add to any microcontroller. Most light sensors just give you a number for brighter/darker ambient lighting. The VEML7700 makes your life easier by calculating the lux, which is an SI unit for light. You'll get more consistent readings between multiple sensors because you aren't dealing with some unit-less values.
The sensor has 16-bit dynamic range for ambient light detection from 0 lux to about 120k lux with resolution down to 0.0036 lx/ct, with software-adjustable gain and integration times.
Interfacing is easy - this sensor uses plain, universal I2C. Adafruit put this sensor on a breakout board with a 3.3V regulator and logic level shifter so you can use it with 3.3V or 5V power/logic microcontrollers.