The #twatch backlight is controlled through a TCP server on port 1337. We use Herculese as our TCP client.

Connect to the #twatch TCP server at the IP address shown on the LCD screen. Send the command 0xFE 0x42 0x00 to turn on the backlight. Send the command 0xFE 0x46 to turn it off. Programs like LCD Smartie and LCDProc send these commands automatically when they start and exit.