Two light sensors located under the speaker grills measure the amount of ambient light in your environment. Based on these measurements, the PowerBook G4 (17-inch) or PowerBook G4 (15-inch FW 800) computer can adjust the display's brightness and turn on the keyboard's illumination.
The display brightness and illuminated keyboard features can be turned on or off independently of each another. For more information on turning off the ALS, see technical document 86270, "PowerBook G4 (17-inch), (15-inch FW 800): How to Turn Off Ambient Light Sensor (ALS)".
Although both of these features are automatic, you can always remain in control. By pressing the function keys F1 and F2, you can adjust the display's brightness level. Once you find a level you like, the computer associates your selection with the current ambient light level. Using this selection, the computer automatically adjusts the display's brightness as light levels change. To change this selection, simply press F1 and F2 and associate another brightness level with another ambient light measurement. To turn this feature off, see technical document 86270: "PowerBook G4 (17-inch), (15-inch FW 800): How to Turn Off Ambient Light Sensor (ALS)".
The keyboard backlight works in a similar way. It turns on when the ambient light is low enough for the backlight to be useful. Once you are in an environment dark enough for the feature to turn on, press the F8, F9, and F10 keys to adjust the associated keyboard backlight level. As the ambient light level increases, the keyboard backlight increases until it reaches its maximum setting then turns off when there is enough room light. For more information, see technical document 86270: "PowerBook G4 (17-inch), (15-inch FW 800): How to Turn Off Ambient Light Sensor (ALS)".
Note: Not all PowerBook G4 (15-inch FW 800) models include the backlit keyboard and ambient light sensor. To determine if your model includes these features see if the F8, F9, and F10 keys have the ambient light sensor icons printed on them.
The display brightness and illuminated keyboard features can be turned on or off independently of each another. For more information on turning off the ALS, see technical document 86270, "PowerBook G4 (17-inch), (15-inch FW 800): How to Turn Off Ambient Light Sensor (ALS)".
Although both of these features are automatic, you can always remain in control. By pressing the function keys F1 and F2, you can adjust the display's brightness level. Once you find a level you like, the computer associates your selection with the current ambient light level. Using this selection, the computer automatically adjusts the display's brightness as light levels change. To change this selection, simply press F1 and F2 and associate another brightness level with another ambient light measurement. To turn this feature off, see technical document 86270: "PowerBook G4 (17-inch), (15-inch FW 800): How to Turn Off Ambient Light Sensor (ALS)".
The keyboard backlight works in a similar way. It turns on when the ambient light is low enough for the backlight to be useful. Once you are in an environment dark enough for the feature to turn on, press the F8, F9, and F10 keys to adjust the associated keyboard backlight level. As the ambient light level increases, the keyboard backlight increases until it reaches its maximum setting then turns off when there is enough room light. For more information, see technical document 86270: "PowerBook G4 (17-inch), (15-inch FW 800): How to Turn Off Ambient Light Sensor (ALS)".
Note: Not all PowerBook G4 (15-inch FW 800) models include the backlit keyboard and ambient light sensor. To determine if your model includes these features see if the F8, F9, and F10 keys have the ambient light sensor icons printed on them.
Figure 1 F8, F9 and F10 keys on keyboard
If these icons are not printed on the keys, then these features are not present in your model.