I've read posts here dealing with how much more power or Watts it takes for a light to appear twice as bright. I've had a chance to do some experimenting with a 300 Watt short arc bulb today. Since buying the Megarays which use a 175 Watt Cermax sealed beam short arc bulb, I've bought a programmable (via a keypad and not changeable once running) 300 Watt and two programmable (changeable from 100 Watts to 500 Watts when running) 500 Watt short arc bench power supplies with ignitors built-in. For fun, I played with the 300 Watt bulb today running off of one of the 500 Watt supplies. In order for my eye to detect the slightest decrease in brightness, I had to crank down power from 290 Watts to about 250 Watts in one swift motion. So it took a 15% decrease in power to see anything. I didn't go lower than 235 Watts because I don't know if it might be detrimental to the bulb. Nothing Earth-shattering, just some data to help understand the relationship between more power and more light - or in this case, the reverse.