N900 light meter
The light meter lets the software on the n900 sense ambient light levels.
Hardware
The device is a TAOS TSL2563.
Software
It is handled by the kernel module tsl2563.
The kernel driver exposes the lux value in the sysfs file
cat /sys/class/i2c-adapter/i2c-2/2-0029/lux 21
Third party applications that use this sensor include Luxus Light Meter.
The sensor is also used to modulate the backlight in response to ambient light.