Light Meter is an application that allows you to select your chosen aperture size, and gives you the appropriate shutter speed according to the light condition. just like a light meter used for photography (see here for more info)

Touching the LCD-style numbers you can set the exposure parameters. If you set the aperture value, speed will be calculated, and vice versa. The LCD-style numbers give you only values permitted by your camera/lens.

You can easily add your camera/lens parameters in the files camera.conf and lens.conf in /opt/lightmeter, then you can select them using the settings menu option.

In the package you'll find only the Nikon D80 and a 16-85 Nikkor lens in the .conf files.

To store the actual exposure you can use the three "memory" buttons. (More to read)