Strange problem with low energy light bulb

[Dave Plowman (News)]

On Wed, 11 Jul 2007 11:58:56 +0100, "Dave Plowman (News)"

Workshops are a different thing - they aren't really a domestic
environment.

Mine is. ;-) It is really a bedroom.

And when mixed with natural daylight, I can see the
point.

Quite. Good domestic lighting supplements or replaces that provided by
god. ;-)

 

[Don Klipstein]

By that reasoning you should really match the color temperature of
moonlight, which is greater than 4500K.

Moonlight's color temperature at its highest is about 4000. It is
usually even less. It is less than that of sunlight because the moon is
not white or gray, but brownish.

Meanwhile, at illumination level so low that color vision does not work
well, color temperature matters less. At illumination levels an order of
magnitude or two or three above that of moonlight, most people like it
warm (lower color temperature).

- Don Klipstein ([email protected])

 

[Don Klipstein]

No argument there, people ARE conditioned to incandescent lights at night,
at the moment.
(which of course are not so different to the lamps and candles that came
before.)
I wonder whether that will be so a hundred years from now though, when very
few people will even remember seeing one. Whether we will always demand to
emulate what we now have, or whether we will accept a gradual change to
something else, IF it is more efficient.
And of course the eyes sensitivity is not it's highest at the red end
either.

Lumens per watt of the portion of blackbody radiation that is in the
400-700 nm range is maximized in the upper 3,000's at about 263 lumens per
visible radiated watt. Apparently, getting into the 5,000's K causes blue
content to increase faster than red content decreases, decreasing the
percentage of the visible light spectral content that is in the
yellow-green range.

This figure is down about 1% at around 3300 and around 4600 K. There is
a lot of freedom in color temperature of a whitish artificial light source
without compromising luminous efficacy much.

- Don Klipstein ([email protected])

 

[Don Klipstein]

You've never seen gaslight, then?

Correlated color temperature generally mid 3,000's, and sometimes looks
a bit cold and spookyish. It's also a bit greener than light from a
blackbody, but usually looks only slightly so in my experience.

- Don Klipstein ([email protected])

 

[Don Klipstein]

Have you never wondered why most prefer the colour temperature of tungsten
for domestic lighting?

Personally, I like more like 3500K at most brighter indoor lighting
levels, closer to 3,000 for dimmer indoor lighting.

Higher color temperature often appears "dreary" unless illumination
level is very high.

People often find it "dreary" outdoors under overcast conditions with
color temperature around 6000 K, especially when illumination level gets
under several thousand lux.

Things can look dreary at dusk and dawn, though people can be in a less
dreary mood outdoors then. At dawn things are brightening, and at dusk
people are likely to be on their way home from work or towards
entertaining activities.

As for why higher color temperature can make things "drearier" at lower
illumination levels:

1. The spectrum is richer in wavelengths favorable to scotopic vision,
which lacks ability to see color. Higher color temperature favors things
looking grayish when illumination level is down to several lux or less.

2. More light of wavelengths favorable to scotopic vision can make your
eye's pupil smaller than otherwise for a given illumination level. 100
lux at 5000 K can make your pupil smaller than 100 lux at 3000 K. (The
lux and other photometric units are defined in terms of photopic vision
and not scotopic vision.) That can make things appear dimmer. This can
also have an effect on color vision if illumination level is down to a few
lux or less, by depriving the color-sensing cones of light.

3. Reds look darker at higher color temperature, and can "drop out to
black" when color temperature is high and illumination level is low enough
to start making photopic vision marginal.

- Don Klipstein ([email protected])

 

[Don Klipstein]

[email protected] (Don Klipstein) wrote in


This makes sense, in a way, though the actual assumption is surely a
misinterpretation. In the context of lasers it makes sense now, because
those are usually monochromatic (or take pumping on narrow bands of lines),
and the maximum efficiency of any 'line' drawn from that lamp will be
around 2% at best. Discussions of efficiency for narrow bands or lines in
lasers or LED's or phosphor or sodium sources dominate a lot of reference
material, so that's probably why this figure arises so often.

Even so, it's harder to see how that hasn't been corrected in something
like Wikipedia by now. I guess a lot of people don't think of light below
670 nm as useful? (If you look at colours on a monitor or TV you can cut
all below about 635 nm). http://www.inchem.org/documents/ehc/ehc/e23_3.gif
shows a diagram that suggests you might lose 25% or so from a 3000K
tungsten emission just by ignoring a big enough chunk of deep red. (More
lost that way than gained by IR supression in tungsten). Still doesn't
explain the 2.6% value on Wikipedia, but if only the dominant 'line' is
taken that wouldn't either because 2.6% would probably be too high, even
for a 110V 100W incandescent.

Wikipedia articles are written by anyone who wants to write them, and
with a few exceptions can be edited by anyone who wants to go in and edit
them - anonymously even, without even creating an account and signing in.

A lot of the heat energy is carried to the bulb by convection and emitted
as IR, so the temperature will be lower than than if the filament was
heated in vaccuum.

It's not an ideal blackbody radiator. That could make a
likely average fall well below 6%, especially if you consider that the
world has a lot of 240V lamps too.

Tungsten deviates from blackbody largely by some supression of infrared,
enough to slightly outweigh heat conduction and convection by the fill gas
in some incandescents.

I think 240V 1000 hour 100 watt would be more like about 5.5%.

15 watt 120V 2500 hour incandescent, at 8 lumens/watt and color temp.
2400K at most, is close to 3%.

The steepness of that curve alone is enough to make large changes in
output of visible lumens with small changes in voltage.

Yes, quite true. But at full voltage most 120V incandescents 60 watts
or more are about 4.5-8% efficient at converting electricity to radiation
in the 400-700 nm range.

In short, I guess that the figure of 2.6% and others similar might not have
been gained by calculation at all, but by measurement. I don't know what
the conditions for that were though, so I can't comment on them.

- Don Klipstein ([email protected])

 

[Lostgallifreyan]

[email protected] (Don Klipstein) wrote in

Wikipedia articles are written by anyone who wants to write them,
and
with a few exceptions can be edited by anyone who wants to go in and
edit them - anonymously even, without even creating an account and
signing in.

Of course. It's also more likely that such an item would be corrected than
vandalised. If we were wanting a verdict on the mental health of Micheal
Jackson the laso place I'd expect to find a sensible judgement would be
Wikipedia but for technical things that don't have any salacious
or celebrity entertainment value it's fairly good, or at least likely to
improve over time.

It's not the only source I rely on either. It's actually slow to load and
not the first I turn to, most times.

 

[Lostgallifreyan]

[email protected] (Don Klipstein) wrote in

Yes, quite true. But at full voltage most 120V incandescents 60
watts
or more are about 4.5-8% efficient at converting electricity to
radiation in the 400-700 nm range.

Is this by calculation or measurement? I was hoping you or someone else
would comment on that from experience with it. Those lower figures are so
common that they must have come from somewhere, and not all from looking
only at the strongest wavelength or omitting something in calculation. I've
never seen claims of 6 to 7% for a 100W lightbulb before, and I'm sure I
would if measurements routinely reported it.

 

[Albert Manfredi]

Have you never wondered why most prefer the colour temperature of
tungsten
for domestic lighting?

It's not tungsten we prefer, I don't think, but rather a color
temperature that's close to that of a flame. That's what the human race
used for artificial lighting for the very vast majority of its
existence. It shouldn't be surprising that we still find it more comfy
than cold lighting, at night.

My warmest CFLs are now 2700 K. Not bad, but I'd still prefer a little
warmer. The 4100 tube fluorescents we have are not in the least
attractive.

Don Pearce posted this:

Nice chart here

http://www.olympusmicro.com/primer/lightandcolor/colortemp.html

Candlelight is 2000 K
60W incadescent bulbs are about 2500 K.
100W are slightly cooler, but still well under 3000 K.
Photofloods, which seem quite cool, are around 3500 K.

Nor surprising that something up around 6000 K would be annoying.

Bert

 

[Lostgallifreyan]

[email protected] (Don Klipstein) wrote in

More like 6-7%. Each watt of tungsten radiation in the 400-700 nm
range
is around 250 lumens.


Figure around 250-300 lumens per watt of "white LED light". Looks
like
those achieve about 20%.

Watts of emitted light? I just saw a later post of yours that mentioned
"lumens per visible radiated watt". I think that's why we're discussing
such different values. I'm talking about input watts. I thought we all
were, at least Eeyore certainly was, as that's ultimately watt (haha) is
consumed no matter watt is emitted.

Cree themselves don't claim anything like 250-300 l/W for input watts, at
least not yet, though that might not be long awaiting.

So how does a 100W incandescent look in that context?

 

[Lostgallifreyan]

[email protected] (Don Pearce) wrote in

Workshops are a different thing - they aren't really a domestic
environment.

Mine is. And the variety of lights I use in it amazing, at times.
Usually incandescent though, when resting.

 

[Lostgallifreyan]

Have you never wondered why most prefer the colour temperature of
tungsten for domestic lighting?

Familiarity, and because it embodies a kind of neat simple magic, a safe
capturing of fire in an idealised form. It's a scientific form that almost
everyone can grasp. It's as iconic as the wheel, it's just not been around
as long.

I guess the truth of 'natural daylight' emulations is that they make people
feel agoraphobic if they can't withdraw from that light. Bring on LED
colour mixing. Or at least a nice emulation of firelight.

 

[GregS]

It's not tungsten we prefer, I don't think, but rather a color
temperature that's close to that of a flame. That's what the human race
used for artificial lighting for the very vast majority of its
existence. It shouldn't be surprising that we still find it more comfy
than cold lighting, at night.

My warmest CFLs are now 2700 K. Not bad, but I'd still prefer a little
warmer. The 4100 tube fluorescents we have are not in the least
attractive.

Most CFL's I have used are too orange for me. I have one of those bargain dollar store
blue ones, and those suck. I bought one at The home Depot many years ago.
paid $20 for a dimmable type. It ended up being the best color I have seen, in my
opinion. They quit selling dimmable lamps. I hate when stores change stocks all
the time, especially Wal Mart.

greg

 

[Lostgallifreyan]

[email protected] (Don Klipstein) wrote in

1. The spectrum is richer in wavelengths favorable to scotopic
vision, which lacks ability to see color. Higher color temperature
favors things looking grayish when illumination level is down to
several lux or less.

2. More light of wavelengths favorable to scotopic vision can make
your eye's pupil smaller than otherwise for a given illumination
level. 100 lux at 5000 K can make your pupil smaller than 100 lux at
3000 K. (The lux and other photometric units are defined in terms of
photopic vision and not scotopic vision.) That can make things appear
dimmer. This can also have an effect on color vision if illumination
level is down to a few lux or less, by depriving the color-sensing
cones of light.

3. Reds look darker at higher color temperature, and can "drop out to
black" when color temperature is high and illumination level is low
enough to start making photopic vision marginal.

All true, but balanced perfectly, whatever the explanations might be, by
the sense of utter dinginess that a dim incandescent or red-heavy CFL
makes. Whether a spectrum favours photopic or scotopic vision, it looks
dire if we have to make an effort to perceive colour and space with it. I
think that the drain on our effort is partly what causes drear. That and a
lack of contrast, which might account for the feeling even in high daylight
illumination. I like LED's better than CFL's because they allow more
natural contrasts, if shone on white paint they are like sky, if direct,
they are like sunlight (though lacking in colour balance). CFL's don't
manage either convincingly at all, I find.

 

[Don Klipstein]

[email protected] (Don Klipstein) wrote in


Is this by calculation or measurement? I was hoping you or someone else
would comment on that from experience with it. Those lower figures are so
common that they must have come from somewhere, and not all from looking
only at the strongest wavelength or omitting something in calculation. I've
never seen claims of 6 to 7% for a 100W lightbulb before, and I'm sure I
would if measurements routinely reported it.

They do lots of photometric measurements, while radiometric figures for
incandescents appear to me to be rather rare. More common than actual
measurements I see comments in the direction of "close enough to
blackbody".

http://www.uwsp.edu/cnr/WCEE/keep/Mod1/Rules/EnConversion.htm
says most incandescents are about 5% efficienct

http://www.iiasa.ac.at/Publications/Documents/IR-04-027.pdf
also gives a 5% figure

Osram says 5% here:
http://catalog.osram-os.com/catalogue/catalogue.do;jsessionid=
337BCEEB510F317E25E607F73C895CFB?act=downloadFile&favOid=
020000020003caf0000100b6

http://www.healthyhomemagazine.ca/light.html
says 4-6%, attributed to someone at Natural Resources Canada.

http://www.eia.doe.gov/kids/energyfacts/saving/efficiency/savingenergy.html
says 10%

http://oikos.com/esb/40/kitlight.html says 10%

10% I find to be a somewhat common figure, though rather optimistic.
Some of those 10% figures may be based on an alternative definition of
visible light as 380-760 nm rather than 400-700 nm.

- Don Klipstein ([email protected])

 

[Don Klipstein]

[email protected] (Don Klipstein) wrote in


Watts of emitted light? I just saw a later post of yours that mentioned
"lumens per visible radiated watt". I think that's why we're discussing
such different values. I'm talking about input watts. I thought we all
were, at least Eeyore certainly was, as that's ultimately watt (haha) is
consumed no matter watt is emitted.

Cree themselves don't claim anything like 250-300 l/W for input watts, at
least not yet, though that might not be long awaiting.

So how does a 100W incandescent look in that context?

I am saying that a watt of white light is about 250 lumens, not the 683
some use as the lumen/watt figure for a 100% efficient light source. A
100% efficient white light source would achieve about 250-300 or so
lumens/watt, depending on what they call "white".

Most of those generating figures of incandescents being 1-2% efficient
are assuming that they would achieve 683 lumens/watt if they were 100%
efficient.

- Don Klipstein ([email protected])

 

[Dave Plowman (News)]

It's not tungsten we prefer, I don't think, but rather a color
temperature that's close to that of a flame.

Err, isn't that what I wrote? It's the colour temperature that matters
rather than the source.

 

[Lostgallifreyan]

[email protected] (Don Klipstein) wrote in

I am saying that a watt of white light is about 250 lumens, not the
683
some use as the lumen/watt figure for a 100% efficient light source.
A 100% efficient white light source would achieve about 250-300 or so
lumens/watt, depending on what they call "white".

Most of those generating figures of incandescents being 1-2%
efficient
are assuming that they would achieve 683 lumens/watt if they were 100%
efficient.

- Don Klipstein ([email protected])

Ok, I see that lumens depend on the spectrum, not just the actual visible
watts emitted, but given that there is convection in an incandescent lamp
that makes some of its power emit in the IR, does enough leave that way to
bring the lumens per input watts down to levels that can account for stated
line-power-to-light efficiences of 3% and lower?

I think when Cree talk of lumens per watt, they're talking of lumens for
each watt of electrical input, and that's how I want to make the
comparison.

 

[Don Klipstein]

[email protected] (Don Klipstein) wrote in


Ok, I see that lumens depend on the spectrum, not just the actual visible
watts emitted, but given that there is convection in an incandescent lamp
that makes some of its power emit in the IR, does enough leave that way to
bring the lumens per input watts down to levels that can account for stated
line-power-to-light efficiences of 3% and lower?

Most of the output of an incandescent is IR.

I think when Cree talk of lumens per watt, they're talking of lumens for
each watt of electrical input, and that's how I want to make the
comparison.

I was only mentioning figures of lumens per watt of visible light output
to explain that an incandescent achieving 17.1 lumens per input watt is
nearly 7% efficient.

Put 100 watts into an incandescent that chieves 17.1 lpw. You get 1710
lumens. Each lumen is about 1/250 watt of "white light", not the 1/683
watt assumed by those claiming incandescents are only 1-2% efficient.

- Don Klipstein ([email protected])

 

[David Harmon]

On Wed, 11 Jul 2007 15:10:28 +0000 (UTC) in sci.electronics.basics,
[email protected] (Don Klipstein) wrote,

Personally, I like more like 3500K at most brighter indoor lighting
levels, closer to 3,000 for dimmer indoor lighting.

Higher color temperature often appears "dreary" unless illumination
level is very high.

Do you put orange gels on your windows?