Re: Strange problem with low energy light bulb

[Mr.T]

Not only that, but pinpoint sources of light have glare.

I think you will find enough glare from reflections during daylight hours.
That's generally the greatest need for sunglasses after all.

Daylight is dispersed.

Not very dispersed on a cloudless day though.

MrT.

 

[Lostgallifreyan]

[email protected] (Don Klipstein) wrote in

So an ideal blackbody at 2865 K receiving 100 watts and radiating 100%
of this produces 6.63 watts of visible light and 1670 lumens. The ratio
of lumens to watts of visible output is 252, not 683.
683 lumens in a watt of visible light is only true for yellow-green
light of wavelength around 555-556 nanometers, where this figure is
maximized. Those saying that incandescents are only around 2% efficient
are assuming that a watt of any kind of visible light has 683 lumens.

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.

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

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.

 

[Dave Plowman (News)]

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

Provided you also match the intensity? ;-)

The eye accommodates gradually to a change in colour temperature. It
doesn't look 'cold' to us at midday and 'warm' in the evening. But does
notice a sudden change in that colour temperature - hence its importance
for film and video etc.

Lighting which is used to replace daylight - like that most of us have at
home for use when daylight fades - ideally shouldn't give such a sudden
change in temperature that it is noticeable. In the same way as lighting
used to supplement daylight - like in say an office - should also be an
approximate match to that daylight. It's common sense, really.

 

[Lostgallifreyan]

Fine, that's why we all get a personal preference. However the spectrum
spread has as much to do with it as the stated color temperature IMO.

Yes. We are better at sensing discontinuities too, than we might think. We
can fool vision with RGB but when presented with purple and monochrome
violet we can see the difference without difficulty. Same goes for the
orange of laser or LED or low pressure sodium, or that made by mixing red
and green. We usually know when we're seeing a pure form of colour, and
it's only conditioning that allows us to easily accept things like TV
screens. (Which chop out all red below about 635 nm, as it happens, as
well as most of the rest of the spectrum).

As far as natural light goes, we are best satisfied by a true continuum
because we adapted to that before we evolved eyes, as such. Take a look at
a Cree or Luxeon LED carefully reflected in a CD. Now do the same with a
CFL. The LED's might be a tad skewed in their distribution but so is
daylight, usually, and LED's make a much better continuum than CFL's do. If
CFL's could do better they probably would, but I haven't seen one that
does.

 

[Don Pearce]

Provided you also match the intensity? ;-)

The eye accommodates gradually to a change in colour temperature. It
doesn't look 'cold' to us at midday and 'warm' in the evening. But does
notice a sudden change in that colour temperature - hence its importance
for film and video etc.

It is more complicated than that. If a cloud suddenly covers the sun,
we don't perceive a change in colour temperature. But if that happens
while filming, the colour change is obvious and intrusive. The thing
is that we are used to the normal interactions with the real world and
respond to all sorts of cues in our surroundings to make instant
adjustments. When sitting indoors watching TV, those cues are not
there, so we can't make the adjustments.

Lighting which is used to replace daylight - like that most of us have at
home for use when daylight fades - ideally shouldn't give such a sudden
change in temperature that it is noticeable. In the same way as lighting
used to supplement daylight - like in say an office - should also be an
approximate match to that daylight. It's common sense, really.

I once bought a "daylight" bulb with a bright blue tint, thinking it
would be better than normal bulbs. It was back in its box within a
day. Lower colour temperatures are now what we consider right for the
evening. The same goes for any indoor lighting - approaches to
daylight for indoor lighting are always received poorly.

d

 

[Mr.T]

The eye accommodates gradually to a change in colour temperature. It
doesn't look 'cold' to us at midday and 'warm' in the evening. But does
notice a sudden change in that colour temperature
Yes.

- hence its importance for film and video etc.

That's more to do with the relative sensitivity of film color layers etc.
They are specifically balanced for Daylight or Tungsten, and are wildly
innacurate when used with the wrong light source.

Lighting which is used to replace daylight - like that most of us have at
home for use when daylight fades - ideally shouldn't give such a sudden
change in temperature that it is noticeable.

It only takes a few minutes for the eyes to adjust.

In the same way as lighting
used to supplement daylight - like in say an office - should also be an
approximate match to that daylight.

Many internal offices get NO daylight, only artificial light. Why would it
matter if it's day or night outside?

It's common sense, really.

Only if you realise that's an oxymoron.

MrT.

 

[Mr.T]

approaches to
daylight for indoor lighting are always received poorly.

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.

MrT.

 

[Don Pearce]

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.

MrT.

Just thought. Some friends of mine have a house in America with a
bathroom right in the centre, which has no windows. They had one of
those sun tubes fitted that brings daylight down from the roof. The
response from guests is always the same. "Why do you have a blue light
in the bathroom?"

d

 

[Dave Plowman (News)]

I once bought a "daylight" bulb with a bright blue tint, thinking it
would be better than normal bulbs. It was back in its box within a
day. Lower colour temperatures are now what we consider right for the
evening. The same goes for any indoor lighting - approaches to
daylight for indoor lighting are always received poorly.

I have daylight fluorescent lighting in my home workshop which also has a
degree of natural lighting. Wouldn't have any other.

 

[Don Pearce]

I have daylight fluorescent lighting in my home workshop which also has a
degree of natural lighting. Wouldn't have any other.

Workshops are a different thing - they aren't really a domestic
environment. And when mixed with natural daylight, I can see the
point.

d

 

[Dave Plowman (News)]

That's more to do with the relative sensitivity of film color layers etc.
They are specifically balanced for Daylight or Tungsten, and are wildly
innacurate when used with the wrong light source.

In which way are they 'inaccurate'? They will look wrong to the eye on a
'cut' but as with real life if all shots are matched the eye will
accommodate. The monitor you're reading this on is unlikely to match
*exactly* another one in colour temperature but will look ok to the
individual. The eye compensates, as I said, as it must do given that
daylight changes. Unless it has a reference to match to.

It only takes a few minutes for the eyes to adjust.

Err, yes. That's what I said. But it doesn't react instantly. Hence it
notices a sudden change in colour temperature. Like switching on 4500K
lights in a house when it gets dark.;-)

Many internal offices get NO daylight, only artificial light. Why would
it matter if it's day or night outside?

Sigh. Same as a house then. If you live underground...

Only if you realise that's an oxymoron.

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

 

[Dave Plowman (News)]

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.)

You've never seen gaslight, then?

 

[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]

Yes. We are better at sensing discontinuities too, than we might think. We
can fool vision with RGB but when presented with purple and monochrome
violet we can see the difference without difficulty. Same goes for the
orange of laser or LED or low pressure sodium, or that made by mixing red
and green. We usually know when we're seeing a pure form of colour, and
it's only conditioning that allows us to easily accept things like TV
screens. (Which chop out all red below about 635 nm, as it happens, as
well as most of the rest of the spectrum).

As far as natural light goes, we are best satisfied by a true continuum
because we adapted to that before we evolved eyes, as such. Take a look at
a Cree or Luxeon LED carefully reflected in a CD. Now do the same with a
CFL. The LED's might be a tad skewed in their distribution but so is
daylight, usually, and LED's make a much better continuum than CFL's do. If
CFL's could do better they probably would, but I haven't seen one that
does.

I have been happier with the color rendering of CFLs than that of most
white LEDs. I have found most white LEDs to make reds and greens appear
duller. I have also seen the color-dulling effect of most fluorescents
with color rendering index outside the range of 82-86 (though high is
better than low). The key here appears to be ratio of yellow content to
red and green content.

- 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.