Are your headlight lenses getting cloudy 2426

Matthew Russotto

Your other points are well taken, but to figure usefulness of a bulb, I think that measuring light output (even if it later gets converted to heat) for wattage input is definitely a measure of its efficacy. Certainly you can see that.

If it getting converted to heat later means you can't count light energy produced as its output, then you could say the same thing about any mechanical enrgy expenditure too. Take, for example, a cooling fan. A certain percentage of the wattage put in immediately goes to heat up the fan motor, the rest goes to moving air - and that is the efficacy (or efficiency if it's energy in per useful energy - energy converted to moving the air - out) of that fan motor - the energy of moving the air around compared to the wattage put in. But - guess what - eventually that air quits moving. WHY? Firction. Unltimately the energy that got transformed into moving that air gets dissipated as heat (friction) of that air motion - that's what sops the air from moving once you turn the fan off. Are you saying that therefore you can't count the very useful and intended motion of that air in its efficacy-efficiency simply because eventually it gets turned into heat?

Same with the energy of burning fuel to move a car. Eventually it all gets eaten up by friction (bearings, tires, brakes) and turns to heat. Yet we don't say the efficiency of a car is zero because all the energy released from the fuel eventually ends up as heat. Pretty much that that is not immediately converted to heat (heating up the coolant, block, various other engine parts, and air moving thru the radiator) that goes into moving the vehicle is what gets plugged into the efficiency formula as the output - even though ultimately it alll gets converted to heat.

So - you're off on this one point. Your other points I think are valid.

Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my address with the letter 'x')