This is a particularily interesting lightsensor - as is reacts to the same range of light as the human eye - and additionally uses a I2C bus that makes interfacing it to a Arduino or a Jeeduino. Indeed the Jeeduino is getting a "shield" that works with this sensor:

The TSL2561 is a light-to-digital converter that transform light intensity to a digital signal output capable of direct I2C interface. The device combines one broadband photodiode (visible plus infrared) and one infrared-responding photodiode on a single CMOS integrated circuit capable of providing a near-photopic response over an effective 20-bit dynamic range (16-bit resolution). Two integrating ADCs convert the photodiode currents to a digital output that represents the irradiance measured on each channel. This digital output can be input to a microprocessor where illuminance (ambient light level) in lux is derived using an empirical formula to approximate the human eye response. The TSL2561 device supports a traditional level style interrupt that remains asserted until the firmware clears it.

[From Advanced Light Sensing Products | TAOS ]