People in the lighting community use Lumens or Candlepower to make the relationship between lamps, fixtures, reflectors and shades.
The problem with using watts is you still need to know how much light the fixture is pushing out and at what distances you’d like to see X amount of lumens. Rating the fixture in (equivolent) watts doesn’t tell me much since my light meter only works in candlpower or lumens mode. Another thing to consider is that watts is figured mathematically and lumens is a tangeable number.
If you need, many fixtures are rated in lumen output these days so finding that information is more readily available than in the past.
Creating a ratio between the wattage of the lamp verses reflecter properties to get a lumen number might be the best way to go at this. When I’m 40 feet from a fixture the only thing I care about are the lumens. The wattage is only a cost concern at this point and lumen output trumps cost, however, I’m concerned about getting the most lumens for the buck.
It would be pretty easy to measure what fraction of the light output is absorbed by the fixture. IMHO the problem is that not all light is equally useful. If you have a lamp that absorbs 50%, but the rest of the light shines directly onto your desk or table, that would be more “efficient” than a fixture that absorbs 20% but redirects the rest upwards into the ceiling.
scr4, it really depends a great deal on the ceiling and what you are trying to light up. If you are trying to light up the room then the second lamp is great. If you are trying to light up a book under the lamp the maybe not.
Right, and that is why we measure in lumens - that’s what the eye sees.
Different coatings on an otherwise same light bulb or lamp can give off different lumens. Coatings, glass, gases, arc, and the color temperature of the light leaving the bulb all play a part as do the reflectors and the lenses. The more I think about the OP the more I realise that wattage means squat when looking at the larger picture, lumens. That is probably why you see lumens as a light output standard rather than watts.
People who read labels are smart enough to compare apples to apples.
That’s sort of my point: just knowing the efficiency of the fixture itself is not very useful, because the amount of “useful” light depends not only on the fixture, but also the environment (e.g. ceiling height and color) and what exactly you’re trying to do with hte light. So just saying “this lamp absorbs 20% of the light, this other one absorbs 40%” isn’t very meaningful.
That’s just not true. Nobody would try to compare two entirely different lamps. Why on earth would they? Would you do that? No. Well, nobody else would either. That’s like saying we shouldn’t rate furnaces for efficiency because one might be in the basement and the other in the garage. Or like saying we shouldn’t rate refrigerator efficiency because one might have a freezer on top and the other on the side. Or that we shouldn’t rate monitor power consumption because one is used in the den at room temperature and the other on a freezing loading dock. People don’t make those apple to orange comparisons. They look at two lamps, which are going to do the same thing in the same place, and one of them will require a bigger bulb to do the same job. That’s apples to apples, and it’s how comparison shopping is done.
–
To all the worry warts who posted above:
Many of you seem so worried about my “agenda”, and my motives, and feel that I am part of the Green Conspiracy that is somehow taking away your options to waste energy and is somehow going to make you change your life for the worse.
But you’ll notice that I didn’t come here to convince anyone to save money. I could never make anyone save money. As one of you said, you have NO lamps in your entire house that could EVER be converted to fluorescent. That’s pretty extreme, but guys: It’s not about you. I don’t care if you waste money. That’s fine. I don’t care. It’s not about you. Progress is made by walking around those who refuse to budge and the saver save and the curmudgeons don’t.
I came asking a scientific question, which at least one person seems to have noticed and answered to my satisfaction. So the rest of you can rest easy. Nobody is taking away your right to refuse to buy lamps of you your choice.
Yes I would. If I were shopping for a lamp to provide ambient light to my living room, I’d look at several different types of lamps: those with opaque shades that use the ceiling for indirect lighting, those with translucent globe-shaped shades, traditional lamp shades that let some direct light onto the floor, etc.
And what would be the point of providing efficiency ratings if you could only compare between same type fixtures? Fixtures of the same type/design would have very similar efficiencies anyway.
OK, perhaps I misunderstood you when I wrote the above reply. Let me try again.
My point is that the same lamp would have different “efficiency” depending on where it’s placed and what you’re trying to use it for. I have two floor lamps in my room; lamp 1 has a translucent shade that emits diffuse light in all directions, and lamp 2 has an opaque metal shade that reflects all light to the ceiling. If the ceiling is a dark color, lamp 2’s efficiency would be very poor, whereas a white ceiling would make it work very efficiently. If the goal is to provide even ambient light for a large room, lamp 2 may be more efficient, but if you want to illuminate a coffee table, lamp 1 is probably better. Do you see why you cannot describe the “efficiency” of each lamp with a single number?
pocelene: Um, why the abrasiveness in your comments? The folks here are just trying to be helpful.
Possibly because a few of us have hinted delicately that very few light fixtures are shipped with opaque black shades and that the difference between standard equivalent fixtures is going to probably be within the 5-10% range – well below most folk’s “not enough of a benefit to make me prefer one over the other” threshold. (I’m willing to be convinced, however – say if the OP can post some web pages showing fixtures that are clearly poorly designed and light wasting without some compensating aesthetic or functional benefit.)
Basically, a fixture that performs exceptionally well with the lumen/watt criterion is likely going to do poorly in ergonomic criteria such as avoiding glare and diffusing light in a pleasing manner.
Our skepticism about this particular metric should not be interpreted as our being against conservation or more efficient light sources (which is apparently how the OP has taken it). It’s just that we don’t think that this metric will prove of any value whatsoever to the informed consumer.
At the end of the day I buy a lamp fixture because I want it to fit in with whatever design exists in the room/house/whatever. At the same time, I may also have a specific need which also must be met – it this merely a decorative fixture where the lamp will be used only when guests are there, or will I be using it every day? I combine all this and eventually arrive at what bulb wattage I will end up using.
If I want to save energy I will compare bulb wattage with intended use. No more. No less. If I am a typical user I will care a rat’s patoot of any energy lost in the fixture, because it’s too hard, untrustworthy and the actual ammount of energy lost irrelevant. It’s so much easier to understand a 100 watt bulb uses more energy than a 60 watt bulb. Period. Of course, I have 100 watt bulbs in the formal living room because the only time we are in there is with guests. All other bulbs are 60 watts or less.
And no energy-saving fluorescent lamps at all in the house for health reasons.
I’ve sort of been following this thread. I think I (finally) understand what the OP is getting at.
I doubt fixture manufacturers give much thought into how the fixture affects the overall efficiency. The reason is that consumers by-and-large don’t care. Consumers really only care about two things: price and aesthetics.
As long as the lamp is safe (UL approved and all that stuff), then a manufacturer’s only concern is to sell the damn thing and make some money. And to sell it, it must be cheap (low price) and it must be appealing to the eye (aesthetics).