Strange problem with low energy light bulb

[Don Klipstein]

You must really hate daylight then!

At usual room illuminating levels in most rooms in most homes, lamps
that match the color of daylight tend to make things somewhat dreary - no
matter what the color rendering index, although higher CRI and any color
distortions being in the "more vivid" direction (common with triphosphor
fluorescents CRI 82-86) tend to help.

"Cool White" fluorescent is 4100-4300 K, generally nominally 4100.

- Don Klipstein ([email protected])

 

[Don Klipstein]

I was asking about LED drivers not CFLs.

CFLs already include those losses in their stated power. LED fans only ever quote the DC
input power required for the 'chip'.

Talk about an uneven playing field !

Linear fluorescents also have nominal wattages not including ballast
losses. Though ballasts for 17 and 32 watt T8 ones and 20 watt T12
ones mostly tend to underpower them a little and fixtures for those tend
to draw close to nominal lamp wattage with ballast losses included.
Same is true with many 22 watt circlines. However, this is not true for
most other linear fluorescents such as most 34 and 40 watt T12 and 15 watt
T8, circlines other than 22 watts, all common wattages 13 watts or less,
30 watt 3-footers, and I think also the new T5 sizes over 13 watts.

- Don Klipstein ([email protected])

 

[Don Klipstein]

I've yet to see a spectrum published for those 'white' leds. I assume it
must be similar to CFLs.

Nichia's NSPW500BS, their longstanding 5 mm white model:
http://www.nichia.com/specification/led_lamp/NSPW500BS-E.pdf

Nichia's NS6W083, a higher power LED:
http://www.nichia.com/specification/led_smd/NS6W083T-E.pdf

Lumileds Luxeon K2:
http://www.lumileds.com/pdfs/DS51.pdf

Cree XRE:
http://www.cree.com/products/pdf/XLamp7090XR-E.pdf

- Don Klipstein ([email protected])

 

[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.

So why do Cree, and Wikipedia, and probably many others, cite only 17 l/W?
Every time I've seen the efficiency expressed as a percentage it's been '1
to 2%'. Wikipedia state 2.6% which is a tad higher than I've ever been told
before, and even that's nowhere near 6-7%! It's not going to be easy to
learn if everywhere I turn there are figures differing by factors of three
or more. What makes all the others I've seen wrong?

 

[Don Klipstein]

[email protected] (Don Klipstein) wrote in


So why do Cree, and Wikipedia, and probably many others, cite only 17 l/W?
Every time I've seen the efficiency expressed as a percentage it's been '1
to 2%'. Wikipedia state 2.6% which is a tad higher than I've ever been told
before, and even that's nowhere near 6-7%! It's not going to be easy to
learn if everywhere I turn there are figures differing by factors of three
or more. What makes all the others I've seen wrong?

I have a homebrew BASIC program with the blackbody function and the
photopic function.

A USA-usual "Big-3" brand 100W 120V "standard frost" or clear
incandescent rated 750 hours average life and with a coiled-coil filament
is rated to produce 1710-1750 lumens, traditionally 1710. (The "Soft
White" version achieves 40 lumens less.)
The color temperature of that one is 2865 K.

My homebrew program says 16.7 lumens per watt (pretty close) and that
6.63% of the radiation is in the 400-700 nm range (the usual definition of
visible light). It assumes an ideal blackbody radiator with all energy
outgo being radiation.

The discrepancy is caused by tungsten having emissivity varying with
wavelength - generally inversely. Infrared radiation is suppressed enough
to get 17.1 lumens/watt instead of 16.7 despite the lamp having some heat
conduction loss. (For that matter, color temperature does not exactly
match filament temperature - filament temperature is slightly lower.)

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.

Assuming my 252 lumens per watt figure for the visible portion of 2865K
blackbody radiation is true for a 1710 lumen 100 watt lightbulb, that
means a 1710 lumen 100 watt lightbulb is about 6.8% efficient at
converting electrical power to visible light (400-700 nm). The truth
won't be far from this.

- Don Klipstein ([email protected])

 

[Mr.T]

Most domestic lighting is used after dark and the colour temperature last
thing in the day is nothing like 4500k.

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

MrT.

 

[Don Pearce]

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

MrT.

Nice chart here

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

d

 

[Mr.T]

Daylight for artificial lighting is rather annoying. Maybe humans have
been conditioned to want warmer lighting at night,

Conditioned, exactly!
Conditioning can be changed, I far prefer daylight lamps. But it does depend
on the application.

I find the 3000K of my CFLs to be barely warm enough.

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.

MrT.

 

[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?