This API is available on Firefox OS for internal applications only.
The MozPowerManager.screenBrightness property defines the brightness of the screen's backlight, on a scale from 0 (very dim) to 1 (full brightness).
Setting this attribute modifies the screen's brightness. Values outside the range [0-1] are not allowed, and an error of type NS_ERROR_INVALID_ARG is thrown if such a value is assigned to that property.
This attribute can be read and written even when the screen is disabled, but the backlight is off while the screen is disabled.
If you write a value of X into this attribute, the attribute may not have the same value X when you later read it. Most screens don't support as many different brightness levels as there are doubles between 0 and 1, so the value's precision is reduced before storing it.
Syntax
var brightness = navigator.mozPower.screenBrightness
Value
Return a number in the range [0,1].
Specification
Not part of any specification.