User talk:Scheinwerfermann
Archives of Past Discussion
Reversion of "efficacy" edits on the HID page.
Hi,
Okay I'm not logged in. I do have a WP account but didn't bother to use it when I made those edits, and just to be consistent I'm not logged in now.
I moved the term "efficacy" from a description of efficiency down to a new paragraph describing HID efficacy, and inserted the word efficiency into the description of their efficiency. You reverted that change on the flawed assumption that I had not read the linked articles. I had already read those same articles (eg on "luminous efficacy") and would like to know why you think the content of those articles contradicts my edit in any way.
Let me explain my point of view. Efficiency is useful work done divided by energy input. That means the same as the text in that paragraph that was talking about "efficacy". Efficacy means exactly the same as effectiveness. In this case, the ratio of visible light power emitted in lumens divided by power input in watts is efficacy since 1) it is only the visible portion that makes the light effective for its task, the rest doesn't count, and 2) this number is always greater than 1.0 and it has units so it cannot be an efficiency rating.
But the non-visible radiation must be included when you talk about efficiency since of all the energy input, most is converted into electromagnetic radiation (which may be useful or not depending on the task) and a very tiny portion is consumed in chemically changing the lamp materials (or else the lamp would work forever). The total power emitted in radiation is less than the total power input. The lamp cannot be 100% efficient regardless of its efficacy, and even a lamp that achieved the maximum possible efficacy will not be 100% efficient.
To see this is correct you only need to think of a heat lamp that keeps food hot at a takeaway counter. It's the same 200 watt light bulb that I could put in my ceiling at home. The efficiency is the same regardless of the application. However if I use the light bulb at home it has a lower efficacy than if I use it to keep food warm because in the latter case it desirable to give off large quantities of heat as well as light. The efficiency is the same because the light bulb will burn out after the same time in both applications.
The original text said: "they give a greater amount of light output per watt of electricity input" and it is important to realise that without being specific about the band of the spectrum, the word "light" in that sentence means all EM radiation and not just the portion useful for stimulating human retinas. In other words, it was describing efficiency and not efficacy.
That's my justification for saying that any ratio of energy output to input is efficiency, but any mention of visible lighting effectiveness is a luminous efficacy. That's consistent with the linked articles, but the original HID text was ambiguous and therefore misleading. What do you think?