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 and photographic light meter.
The sensor is also used to modulate the backlight in response to ambient light.