Indicates how bright the screen's backlight is, on a scale from 0 (very dim) to 1 (full brightness); this value is a double-precision float.
You can read and write this attribute 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. The value's precision might be reduced before storing it.
screenBrightness = window.screen.mozBrightness
|Feature||Chrome||Firefox (Gecko)||Internet Explorer||Opera||Safari|
|Basic support||?||12.0 (12.0)||?||?||?|
|Feature||Android||Chrome for Android||Firefox Mobile (Gecko)||IE Mobile||Opera Mobile||Safari Mobile|
|Basic support||?||?||12.0 (12.0)||?||?||?|
In order to use
screen.mozBrightness you have to set the preference "dom.screenBrightnessProperty.enabled" to true in about:config.
Not part of specification.