I wonder which color LED would be most visible to dark-adapted
> eyeballs at very low current.
> John
I'm not sure "visible to dark-adapted eyeballs" is the best critieria.
Assuming you don't turn the light on in the bathroom ( triggering some daylight brain chemistry) you don't want the LED wavelength to cause serotonin production. A *quick* search came up with blue light causing the production of serotonin. * emphasis on quick.
I'm might place them at them on the post near the floor so when you walk in, you get in bed between them, but they aren't noticable when in bed.
As a side note I notice my son has some nerf glow in the dark darts stuck to the ceiling light in his room. They charge up when the light is on and glow when he goes to bed. Maybe a couple of these spaced properly could give you the orientation needed. Mike PS. Only slightly related to your problem, but a very interesting article about the eyeball and perception of lighting level.
Very discouraged by past observations of replacing 100w incandescents with "100w" CFLs and very encouraged by your link, I went out and bought a 100w CFL specified at 6500K. I was disappointed again.
I put a cheapy light meter on the end table facing up under the table lamp. I did not move the meter between lamp changes and there was no other source of light in the room. I also made sure that I was far enough from the area such that there were no reflections from my clothes to taint the readings. In addition, I waited for the readings to stop increasing after turn-on and then waited 5 minutes more.
100w incandescent: 302 lux Old 3500k CFL: 150 lux New 6500k CFL: 170 lux
Contrary to the article, the area around the lamp appeared brighter to me with the old 3500k CFL than with the new 6500k CFL. Both CFLs appeared
*much* dimmer than the 100w incandescent.
My personal feeling is that the public is being fed a lot of lies to save energy.
My opinion is that they're not lies, but rather exaggerations: If I want the equivalent of a 100W incandescent, I'd figure on about 33W in a compact fluorescent bulb, i.e., a 3:1 efficiency ratio. A lot of advertising would have you believe that a 4:1 or even higher is viable, but that hasn't been my experience.
Still, even a 3:1 ratio is a huge increase in efficiency. There'd be partying in the streets if gasoline engines suddenly obtained 3x or even 2x as much fuel efficiency as they do now...
Given that the greenies are coming I've been buying case lots of 130V incandescent's (bulb/flood/spot) and halogens floods; and 12V outdoor halogens. SCREW the greenies. I figure on having replacement bulbs thru both Obama's terms... and my retirement funds are safe ;-)
...Jim Thompson
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| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
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- Alexis de Tocqueville
I think the article was about how the "eye" responds to the different temperature light. But now that you have the meter involved your comparing a 302 lux bulb to a 170 lux bulb.
I would suggest you not have the bulb in your eyes view, the article (IIRC) is about reflected light (ceiling fixtures).
I didn't think the authors had a bias in their research. (maybe I'm being naive) :-) Mike
Well, lux is a measure of light based on the eye's sensitivity curve. But the article comments that that curve may be wrong, if I understand correctly. That's why I also made a personal eye observation and evaluation.
I did not have the bulb itself in view, Mike. I was looking at the reflected light in "the area around the lamp" which has a shade on it to prevent direct viewing of the bulb while allowing light from the bulb to escape at the bottom thus illuminating the surrounding objects.
Perhaps not. But, as I was taught in school, it should be standard procedure to question the veracity of a source of information. Motives are sometimes well hidden.
The real problem to me is that even the city where I live is pushing for everyone to replace the incandescent bulbs to save energy. The stores are promoting it. Everywhere I turn they are promoting it. And everyone is saying that these replacements are just as bright as their equivalent wattage ratings imply. It is simply not so, neither by meter nor by eye. I could live with it if a meter said so, but it doesn't. But everybody believes it because the city says so, because the manufacturers have it printed on the box it comes in, and even the TV says so.
The nominally 25W power consumption CFLs are brighter than 100W incandescents. The 20W ones are close (or at least the good ones are). If you buy poor quality ones you may be disappointed and price isn't a useful guide. I have had good cheap ones and even the odd free sample. Main annoyance with them is that dimming isn't easy.
ugh
on.
Part of the problem may well be that the angular distribution of the light from a CFL (particularly the ones with a folded rectangular tube) is quite different to that of a filament lamp. Directly under the filament lamp you see the entire filament and so the brightest output. By comparison for the long thin CFL tube style you are practically looking at it end on and see a comparatively small area direct emitter plus scattered light from the shade. It could easily account for the differences you observe based on emitter geometry.
I suspect if you measured the CFL output in line with the centre of the tube long axis you will get a more respectable result. Although I do tend to agree that nominal light output tends to be overstated.
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I think you have a systematic error in the way you are measuring them. And some CFLs are definitely better than others - it pays to shop around until you find a decent brand at a good price.
The nominally 25W power consumption CFLs are brighter than 100W incandescents. The 20W ones are close (or at least the good ones are). If you buy poor quality ones you may be disappointed and price isn't a useful guide. I have had good cheap ones and even the odd free sample. Main annoyance with them is that dimming isn't easy.
"Part of the problem may well be that the angular distribution of the light from a CFL (particularly the ones with a folded rectangular tube) is quite different to that of a filament lamp. Directly under the filament lamp you see the entire filament and so the brightest output. By comparison for the long thin CFL tube style you are practically looking at it end on and see a comparatively small area direct emitter plus scattered light from the shade. It could easily account for the differences you observe based on emitter geometry."
"I suspect if you measured the CFL output in line with the centre of the tube long axis you will get a more respectable result. Although I do tend to agree that nominal light output tends to be overstated."
Perhaps. But who cares? The selling point is that you can replace the incandescent in whatever fixture with an equivalently rated CFL and get just as much light. No way. By the way, the CFL tube is in a spiral and occupies somewhat the same volume as the incandescent.
I think you have a systematic error in the way you are measuring them. And some CFLs are definitely better than others - it pays to shop around until you find a decent brand at a good price.
Regards, Martin Brown
How can it be a systematic error when the point is that replacing the incandescent with an equivalently rated CFL is supposed to produce the same effect? The important thing is that I get the same light under the same circumstances. Is that not so? If I am reading a book beneath a lamp with a
100w incandescent and I replace the bulb with one of those "100w equivalent" CFLs they tout, reading should be just as easy. It is not. I could also replace the 100w incandescent with a 60w incandescent to save power and get the same effect I've been getting with CFLs. But, that's not the point, is it?
John, I agree there is a big push on these bulbs. Early on I didn't like the color but as they improved they made them look more like an incandescent. I find they work fine for me, I especially like the reduced heat, I have some 4 bulb fixtures on fans that produced way to much heat down here in Florida. Mike
Yes, I agree with you on color and heat. Two very good points. I just feel insulted that they are all saying that it has the same output intensity when it is patently not so.
If I could find one with about 40 or 50 watts (real, not "equivalent") I'm certain I would be happy. *That* I can easily live with.
Within the last 30 minutes I finished replacing the ceiling fixture in my tiny office and threw the switch. The old fixture is the kind that uses two
60w incandescents and the new one uses one 32w Circline fluorescent and one
40w Circline fluorescent. So, I replaced 120w of incandescent lighting with
72w of fluorescent lighting. It is at least as bright as before, it is more daylight-colored, and I'm extremely pleased. The power ratio is about what I thought it might take to make me happy based on my earlier measurements.
It could also be that the el-cheapo light meter is also seeing a significant IR contribution from the thermal filament in the incandescent bulb. You should filter for visible band only.
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You have to allow for some exaggeration by the marketting droids.
A rough guide based on the ones I have around here is that if you buy sensibly you can find CFLs that are slightly better than 4x more efficient in light output per watt. So a
25W CFL beats a 100W incandescent
15W CFL beats a 60W 9W CFL beast a 40W etc. The best 7W CFL candle imitations are now close to 40W equivalent. I don't know how the US marks equivalent wattage but a bit like film ASA I expect they tend to exaggerate performance.
A rough guide is CFL light output is 4x nominal power consumption (and nearly 5x on the very best ones). You can buy really bad ones that are not even 3x presumably due to cheap and nasty phosphors and/or control electronics.
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The total *visible* light output from the device can be the same but you are measuring it in a position where the CFL is not as bright. There is also the issue of powerful IR emissions from a hot filament lamp. How much that affects your light meter readings will depend on the photo detector technology used in it.
It could also be that the el-cheapo light meter is also seeing a significant IR contribution from the thermal filament in the incandescent bulb. You should filter for visible band only.
You have to allow for some exaggeration by the marketting droids.
A rough guide based on the ones I have around here is that if you buy sensibly you can find CFLs that are slightly better than 4x more efficient in light output per watt. So a
25W CFL beats a 100W incandescent
15W CFL beats a 60W 9W CFL beast a 40W etc. The best 7W CFL candle imitations are now close to 40W equivalent. I don't know how the US marks equivalent wattage but a bit like film ASA I expect they tend to exaggerate performance.
A rough guide is CFL light output is 4x nominal power consumption (and nearly 5x on the very best ones). You can buy really bad ones that are not even 3x presumably due to cheap and nasty phosphors and/or control electronics.
The total *visible* light output from the device can be the same but you are measuring it in a position where the CFL is not as bright. There is also the issue of powerful IR emissions from a hot filament lamp. How much that affects your light meter readings will depend on the photo detector technology used in it.
Regards, Martin Brown
You remind me of my dog, Martin. I tell him things and he just stares at me. There is no understanding. Looking into his eyes is like looking into two hollow, bottomless pits.
Look up LUX. Make your own measurements. Do your own experiments.
The meter's sensitivity curve can easily be "off". Meters with claims to be corrected to the "photopic function" may not be corrected very well. Meters without such claims can easily have a spectral sensitivity curve very different from the human photopic function.
The brightest 25W CFL I have ever heard of is Philips SLS "triple arch"
- 1750 lumens. That is top end of non-halogen 100W 120V incandescents.
The max for a 20W CFL is about 1250 lumens or so last time I checked. That is hardly above top end of the range of non-halogen 75W 120V incandescents.
CFLs can be dimmer at non-optimum temperature and after fading for a thousand hours or more.
And at lower illumination levels with warmer color CFLs (color temp.
2700 K), the lower scotopic/photopic ratio of the CFL can make it appear slightly dimmer than an incandescent with equal photometrics (photometric units are defined in terms of "standard human photopic vision" [my words]).
My experience is that a CFL that photometrically matches the best 100W incandescent (the best ones of 25-26 watts) will successfully replace an average 100W incandescent, and even then only usually. Different light distribution pattern and different shape/size of the light producing area will cause problems in some fixtures.
I have always felt that scotopic/photopic ratio has been overemphasized.
I expect the 6500K one to be a more effective yard light or nightlight for a large hallway or large basement than the 3500K one or a 2700K one (whose s/p ratio is lower still), but s/p ratio appears to me to have only a slight effect on effectiveness of illumination at most typical indoor illumination levels.
At times it appears to me that higher s/p ratio backfires - by causing the eye's pupils to constrict and let in less light, so that things appear dimmer.
Meanwhile, higher color temp. CFLs tend to have slightly less photopic output than lower color temp. ones. The "cheapy light meter" is probably incorrect due to likely having a spectral response curve significantly different from that of human photopic vision.
And quite a bit more than the typical 1200-1400lm output of a 100W
230v thinner filament incandescent typical of the European market. The higher voltage makes quite a difference to lumens per watt on filaments.
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Not all 100W filament lamps are created equal (and the long life ones are dimmer still).
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But about the same as some nominal 100W 230v incandescents.
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The emitter geometry certainly plays a part. The nominal output in lumens is clearly a measure of total integrated light output and it says nothing about the actual distribution.
CFL "spotlamps" are incidentally pretty useless - I bought one out of curiosity to try in a closeout sale of bankrupt stock. Certainly not worth paying full price for. Useful when the last real spot blows though as some light is better than nothing.
OK, you are correct on that point, noted well from UK.
Sadly true, and max for a 20 W CFL is indeed almost average for a UK
100W incandescent being operated at 230V. (Is not line voltage in most UK homes closer to 240 in actuality, good for having incandescents brightening by about 7-8% more than CFLs do from the higher-than-nominal voltage?)
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