Originally Posted by
khearn
Ummmm, no. Light bulbs don't have a constant wattage regardless of voltage. If anything they have a constant resistance. Voltage = Amps * Ohms. So if you increase the voltage, you'll increase the current (and also increase the wattage, which is why they get brighter). If a 10W bulb at 12V draws .8A, then it's got a resistance of 15 ohms, and the same bulb at 14.4V would draw .96A. It would now be using 13.8W, so I doubt it would really be putting out twice as much light.
That assumes the resistance is the same, but it might change a little because the lamp would be running hotter. But it's probably fairly close.
Keith
You are right. I forgot about the wattage change. But it's not as great a magnitude as you have. Nor is the amperage draw.
For a 10 W bulb at 12 V, the current is 0.8A. Overvolted by 20% to 14.4V, the current is 0.9. Hardly enough to "eat" the batteries. The wattage goes from 10 W to 12.4W.
The real gain is in the heat of the filament. Hotter filament, more light, less life.
Here's a GE sheet on halogens. Look on page 8 for the lumen output. At 20% overvoltage the lumen output goes up 185%