The screen tends to be one of the biggest consumers of electricity. How much of this is for the backlight vs the actual screen, particularly in the case of an LCD?
Not only the screen is a main consumer. Based on the Motorola Droid, I can give you some data to compare:
Video recording 1557 mW UMTS Upload 1410 mW UMTS Download 1349 mW EGDE Upload 1179 mW WLAN Download 1158 mW Video play (fullscreen) 1135 mW (already minus the display) UMTS phone call 983 mW Camera 934 mW EGDE Download 853 mW Bluetooth receive 751 mW Display (at max) 730 mW GPS Search 550 mW GSM phone call 511 mW Bluetooth send 487 mW WLAN Upload 479 mW Display (at min) 310 mW MP3 play 160 mW UMTS Standby 18,3 mW GSM/EDGE Standby 11,6 mW WLAN Standby 7,8 mW Bluetooth Standby 2,8 mW GPS Standby 0,4 mW
As you can see, there are clearly compontents/actions with a much higher energy consumptions -- but the display gives you good potential to reserve some.