Daniel J. Stern
OT Article on KatrinaI know this is quite OT, but given the amount of Katrina talk going on in the group, I thought you'd all be interested. If somehow you had not yet heard of...
I'm under the impression that "efficiency" (in any engineering context) is always some desired output for a given input, and, for a given process, device, or technology, it only remains for the exploiters of that technology to precisely determine what the desired output and the input (typically cost and-or energy) is, and thus to define the formula for efficiency in the context of that process, device, or technology. I think any engineer would accept the lumens out over wattage in as the efficiency. The fact that the lighting industry has chosen the use the word "efficacy" instead is fine, and anyone who works in the industry would simply be being obstinate to try to insist that it only be called only one or the other. Technically either one is correct.
Hmmm - heres what my Websters says: Efficacy: Power to produce effects or intended results; effectiveness. Efficiency: (1) Ability to produce the desired effect with minimum of effort, expense or waste; quality or fact of being efficient. (2) The ratio of effective work to the energy expended in producing it, as of a machine; output divided by input.
That last sentence is why I say they can be used interchangeably: Output (lumens) divided by input (watts). Lumens represents light energy. Heat is the loss between input and output for lighting as well as in a machine (friction).
Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my address with the letter 'x')
