Here is a key for some of the indicator symbols and lights on various Tablets.

Fujitsu T4020

Figure copied from page 17 of the "T4020, T4020D User's Guide". More details on are also available there.

• Power Indicator - This indicator relates to the computer being on not if it is plugged into a wall outlet.
• Steady On: Tablet is on a ready to use.
• Flashing: Tablet in Standby mode
• Off: Power is off. Tablet is shutdown or in Hibernate mode.
• External Power - This indicator is on when your Tablet is connected to an external power source. If it is off, computer is running on batteries. If the indicator flickers, check that your power adapter is firmly plugged into the back of your computer and an AC power source. If it appears to be firmly plugged in but the indicator still flickers, please bring your tablet and AC adapter to the Taub Tech Center to see if the it needs repair.
• Battery 1 and 2 charging indicators- Indicates batteries are charging. Batteries will charge whether computer is on or off. (They will charge faster while comptuer is off.)
• Battery 1 and 2 Level indicators - These show how much power (by percentage) is available in each battery. If an overcurrent is detected, the battery stops charging and the indicator blinks at a rate of once per second. To stop the indicator from blinking, disconnect the power adapter.
• Wireless LAN - Indicates that the wireless network card is on. Does not indicate whether you have a usable wireless connection. You can turn the wireless network card (and indicator) on with the Wireless switch on the left side of the part of the computer near the keyboard.