What about attaching it to a weapon or holding it in your hand? Stand alone entity, you must find it to use it. Same with the batteries. You can find the light, then the batteries, the batteries can be scripted to last XX amount of time, as the time fades, the light dims, turning it off will save battery, then you must find fresh ones. Change the cone for the light emission and allow changes for color. Bright white when fresh batteries are installed, yellow as they drain out, then obviously, back to darkness.
Case: Antec 900, Mobo: Asus Sabertooth 990FX, CPU: AMD T1100 Thuban 6 core @3300 ghz stock settings, COOLER: Thermaltake Frio, MEM: G Skill Ripjaws X series DDR 3 @ 1866 9-10-9-28, HDD: 2 Western Digital caviar Black 750 Gb set in RAID 0, GPU: Saphire HD 6950 flashed with 6970 bios, PSU: Corsair CX750M, MS: Cyborg Rat 7, KB: Logitec G510, OS: Windows 7 home premium 64 bit.