On Wed, 07 Sep 2005 16:34:03 -0500, Steve wrote:
~fbloogyudsr wrote: ~ ~> "Bill Putney" wrote ~> ~>> Matthew Russotto wrote: ~> ~> ~>>> All the light is ultimately absorbed and converted to heat. ~>>
~>>
~>> 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. ~>> ... ~>> 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. ~> ~> ~> That's not really a very good analogy, Bill. ALL the output of ~> a light bulb is electromagnetic radiation - visible or infrared light. ~> SOME of the (heat) energy from a IC motor is converted to ~> physical work (acceleration of the car). ~ ~ ~Which EVENUTALLY gets converted to heat, either when you step on the ~brakes (flat land) or eventually travel back downhill to the same ~elevation you started at and step on the brakes. ~ ~I think its a pretty good analogy. Yes, EVERYTHING that causes a ~conversion of energy will ultimately just result in a slight increase of ~ the entropy of the universe, whether it be turning on a light bulb, ~driving a car, or the solar radiation from a star. But in the interim ~period, you can distinguish between a "useful" output (the visible light ~portion of the spectrum as it emanates from a light bulb filamant) vs a ~sort of "direct to waste" output (the thermal radiation from an ~incandescent lamp). ~ ~> FYI, one reason that fluorescents aren't 100% "efficacy" (if you ~> will ;->) is that most emit some portion of their output in the UV ~> portion of the spectrum (usually a pretty small amount, some ~> more than others. That's why many are behind diffusers of one ~> kind or another.) ~ ~And they also put out heat- feel a running fluorescent tube. You can ~keep your hand on it (unlike an incandescent lamp of identical input ~power) but it is warm. And the ballast gets warm as well. ~
Back to high school physics. Energy can never be created or destroyed, but it can be converted into other forms of energy. Heat to Light etc.