Yup It's true if using Halogen bulb regardless voltage. I've tried 12v 150watt Projection Halogen bulb (one w/ glass reflector) that friend gave it to me. Using 12v automotive battery, It won't even shine bright like It does on 120v projector (w/ stepdown transformer). I figured it would works better with 12v AC not DC. I hooked thick wire from bulb terminal to battery directly w/ Alternator running LOL.. I was young back then.. Automotive Backup 12v Indescandent bulb is bright and it's about 50 watt. I used to have 70's telescopic desklamp that use stepdown transformer tightly built inside 3" x 3" x 3" cube shaped metal base w/ telescopic pole and a black "Tennis ball" sized bulb reflector using 12v automotive backup lamp. It is bright enuf for reading or do minature project.
I agree w/ Ohm's law. Newer lamp that use Luxeon LED would use far less voltage (they're between 1 to 5 watt average) but yet bright enuf to shine the room with proper lens. They're still under development tho.. Problem is that it have blueish to purpleish hue which are common problem with White LEDs. Nicha LED is the only high quality LED that shine white with no hue and are a little pricey..
