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Best color type of triphosphor tube?

W

WM

Jan 1, 1970
0
I am in the UK and am not a lighting specialist. Treat me gently!

I read the posts in a recent thread in this group and am interested
in trying out a triphosphor tube at home as a light for my home
office because I understand that the triphosphor tube shines brightly
and gives a very natural light.

(1) Can I simply swap in a T8 triphosphor tube where I had an
ordinary (halophosphate?) T8 tube. Or do I need to check something
else? Is it better to buy a whole light than just the tube?

(2) I would like to have the triphosphor give a light as close to
daylight as possible but all I can find is something called "colour
rendering index". I got confused after reading this:

----------------------- QUOTE --------------------------
Fluorescent lamps typically have CRIs in the range 55-85, with 80-85
being classed by the manufacturers as 'good' or 'very good' colour-
rendering.

I beg to differ! To my critical eyes, LIGHT FROM 'TRIPHOSPHOR'
FLUORESCENTS WITH A CRI OF 80-85 IS GHASTLY; extremely flat and
lifeless. By comparison, a nice incandescent quartz-halogen spotlight
really gives vitality to whatever it shines on!

[from http://www.techmind.org/colour/coltemp.html] My capitals.
----------------------- UNQUOTE --------------------------

Hey, now that really confuses me. Maybe a light source that is
genuinely close to daylight paradoxically looks unnatural when it is
the sole source of light.

Also I read in this group:

I use a 300W floodlight with glass front and wire shield above
my workshop bench. I like the heat and sheer intensity of the
light which feels like working in the sun. This is particularly
nice in the winter. The GENUINELY FULL SPECTRUM OF A TUNGSTEN
HALOGEN LAMP would make it the ideal SAD lamp.
[my capitals]

Can someone kindly advise me how to understand this info! Am I
better staying with the tungesten halogen floodlight I am using
rather than going to triphosphor?

Thank you.
 
C

Clive Mitchell

Jan 1, 1970
0
WM said:
Can someone kindly advise me how to understand this info! Am I better
staying with the tungesten halogen floodlight I am using rather than
going to triphosphor?

It depends on your application. Tungsten halogen is much less efficient
than fluorescent but gives a rich warm light with a bit of heat too.

The colour rendering index issue is down to the fact that fluorescent
tubes do not put out an even spectrum of light but have strong peaks in
the primary colours to make white. This means that some incompatible
colours look ghastly under fluorescent light.

Beware the sales pitch that tries to sell you expensive fluorescent
lamps with "full spectrum" output. They are purely trying to sell their
lamps.
 
V

Victor Roberts

Jan 1, 1970
0
I am in the UK and am not a lighting specialist. Treat me gently!

I read the posts in a recent thread in this group and am interested
in trying out a triphosphor tube at home as a light for my home
office because I understand that the triphosphor tube shines brightly
and gives a very natural light.

But some are better than others.
(1) Can I simply swap in a T8 triphosphor tube where I had an
ordinary (halophosphate?) T8 tube. Or do I need to check something
else? Is it better to buy a whole light than just the tube?

You can swap the tubes - what we call lamps. You do not have
to change the fixture (in the US and Canada) or fitting (in
Europe) - what you call the light. lamps with tri-phosphor
are electrically identical to lamps of the same type
(wattage, length, diameter and starting mode) that use
halophosphate phosphors.
(2) I would like to have the triphosphor give a light as close to
daylight as possible but all I can find is something called "colour
rendering index". I got confused after reading this:

You need to look at the Color Temperature or CCT in addition
to the Color Rendering Index or CRI. Daylight CCT's would be
5000K to perhaps 6500K. Incandescent lamps have CCTs of
2700K to 3000K. Typical fluorescent lamps used in offices
have CCTs of 3500K +/- 500K.

----------------------- QUOTE --------------------------
Fluorescent lamps typically have CRIs in the range 55-85, with 80-85
being classed by the manufacturers as 'good' or 'very good' colour-
rendering.

I beg to differ! To my critical eyes, LIGHT FROM 'TRIPHOSPHOR'
FLUORESCENTS WITH A CRI OF 80-85 IS GHASTLY; extremely flat and
lifeless. By comparison, a nice incandescent quartz-halogen spotlight
really gives vitality to whatever it shines on!

[from http://www.techmind.org/colour/coltemp.html] My capitals.
----------------------- UNQUOTE --------------------------

Hey, now that really confuses me. Maybe a light source that is
genuinely close to daylight paradoxically looks unnatural when it is
the sole source of light.

Well, most people find that a fluorescent lamp with CRI of
85 is quite good, but as has been stated, the lamps do not
generate all colors so some fabrics or objects may not look
quite right under tri-phosphor lamps. I have never had a
problem, but others have.

Also I read in this group:

I use a 300W floodlight with glass front and wire shield above
my workshop bench. I like the heat and sheer intensity of the
light which feels like working in the sun. This is particularly
nice in the winter. The GENUINELY FULL SPECTRUM OF A TUNGSTEN
HALOGEN LAMP would make it the ideal SAD lamp.
[my capitals]

Can someone kindly advise me how to understand this info! Am I
better staying with the tungesten halogen floodlight I am using
rather than going to triphosphor?

Thank you.

As has been stated a tungsten lamp generates a continuous
spectrum which can produce superior color in some
applications, but uses 4 to 5 times as much energy as a
fluorescent lamp for the same amount of light. And you will
not be able to find a tungsten lamp with a daylight CCT,
except perhaps for lamps used for some photography
applications that have very short life.

--
Vic Roberts
http://www.RobertsResearchInc.com
To reply via e-mail:
replace xxx with vdr in the Reply to: address
or use e-mail address listed at the Web site.

This information is provided for educational purposes only.
It may not be used in any publication or posted on any Web
site without written permission.
 
V

Victor Roberts

Jan 1, 1970
0
Colour Temperature or more exactly Correlated Colour Temperature for
fluros because they do not have a continuous spectrum affects how the
light appears. Candle may be about 2,000 Kelvin, tungsten halogen lamp
3,200K, daylight fluro may be as high as 6000K or more, higher CT
looks bluer which may appear cold.

You can get fluro tubes with a high CRI and lower CT.

CT is measured in degrees Kelvin because it is defined by the colour
emmited by a platinum element being heated to these temperatures and
there my Planckian physics runs out, over to you Vic...

Too late for Planckian physics, but the Color Temperature is
given in K because it is defined as the color of the light
emitted by a black body at that temperature, measured in
degrees K. The sun is a pretty good black body and has a
surface temperature of about 6000 C or ~ 6300 K. The color
temperature of sunlight at the surface of the earth varies
with time of day and the amount of particulate matter in the
atmosphere.

--
Vic Roberts
http://www.RobertsResearchInc.com
To reply via e-mail:
replace xxx with vdr in the Reply to: address
or use e-mail address listed at the Web site.

This information is provided for educational purposes only.
It may not be used in any publication or posted on any Web
site without written permission.
 
S

Simon Waldman

Jan 1, 1970
0
WM said:
I am in the UK and am not a lighting specialist. Treat me gently!

I read the posts in a recent thread in this group and am interested
in trying out a triphosphor tube at home as a light for my home
office because I understand that the triphosphor tube shines brightly
and gives a very natural light.

(1) Can I simply swap in a T8 triphosphor tube where I had an
ordinary (halophosphate?) T8 tube. Or do I need to check something
else? Is it better to buy a whole light than just the tube?

Just the tube. It is possible that you are already using a triphosphor
lamp though - check what it says on the tube. Depending on the
manufacturer, there will usually be a three-digit number - e.g. 830.
This refers to the colour.

The first digit refers to the colour rendering index. The higher this
is, the smoother the spectrum of light from the lamp, and so the less
distortion of colours. Triphosphor lamps will usually be Colour 8xx or
9xx, wheras older ones may be 6xx or may have a two-digit number (or no
number at all). There is a trade-off between the two triphosphor ranges
in that colour 9xx lamps, while providing better colours, usually
provide less light for the same input of electricity than the 8xx versions.

The second and third digits refer to the "colour tempereature", which is
a way of measuring how "warm (yellowish, low colour temperature)" or
"cool" (blueish, high colour temperature) the light is. If you want to
try to replicate UK daylight in colour you would probably want to look
at 6500K tubes (colour 865 or 965). However you may find in practice
that this gives a very harsh and lifeless light that reads as blue or
even greyish to the eye. IME it seems that the human eye doesn't like
daylight colours at less than daylight intensities! In this case you
should probably try a 3000K or 4000K lamp (for a warm or cooler effect
respectively).

If you're prepared to buy a few lamps and try them out, then for a home
office I'd suggest trying colours 830, 840 and 940 and seeing which you
prefer. Osram sell these in the UK in their "LUMILUX" range for 8xx, and
"LUMILUX Deluxe" for 9xx. Other manufacturers such as Philips will also
have equivalent lamps.

Hope this helps.
 
C

Clive Mitchell

Jan 1, 1970
0
Adam said:
Personally have low voltage tungsten just about everywhere apart from
utility lights, hall etc which are compact fluorescent, be interested
in what other contibutors to the group use themselves?

CFL for general areas, tungsten for functional areas and LED for 24 hour
ambient lighting.
 
Z

Zak

Jan 1, 1970
0
Adam said:
Two seperate issues , Colour Rendering Index, CRI, is a measure of how
accurately a lamp renders colours compared against daylight. A tungsten
lamp has a theoretical CRI of 100 because it emits light in rleatively
equal parts right across the visible spectrum.

ISTR an incandescent lamp has a CRI of 100 by definition.
Colour Temperature or more exactly Correlated Colour Temperature for
fluros because they do not have a continuous spectrum affects how the
light appears. Candle may be about 2,000 Kelvin, tungsten halogen lamp
3,200K, daylight fluro may be as high as 6000K or more, higher CT
looks bluer which may appear cold.

The less light, the lower CT people generally prefer. But this is also a
cultural thing: cold countries like the warm (sunny or flame?) color of
low CT, and hot countrries like the bluish, shadow-colored high CT light.

It might have to do with intensity as well.
Third bit to story Intensity, what you want is to be feeling is as if
your working in sunlight, so you want your good CRI you possibly want a
lower than 6000K light which feels a bit like a bright but cloudy day
and you want lots of it.

And you want a smallish source. This is what makes halogen 'shine':
glossy things look glossy.
Fluros kick tungsten into weeds with efficiency , loads more light out
for your watts in, so for an energy budget they win, but have the
above noted problems.

Tungsten isn`t as efficient but has the above noted advantages.

How would metal halide be for the OP? Nice and bright, point source, and
CRI and CT are available within his desired range.
Personally have low voltage tungsten just about everywhere apart from
utility lights, hall etc which are compact fluorescent, be interested
in what other contibutors to the group use themselves?

I try to avoid incandescent lamps - energy costs are just too high.
Strange how many fixtures are sold that cannot take a compact
fluorescent. Even worse that most fixtures seem not to be made for
lighting but for decoration.

For some fixtures it may be hard to achieve the desired effect,
sparkling and bright, with the CFL, but it must be possible, and there
should be a market for those things.

Light quality depends a lot on the fixture and/or diffuser, because
these change direction of light, glare and color. Halogen is easy in
that regard because it is small and can be had with integral reflector.
Glare is a problem but the actual source is easy enough to shield.

CFL is hard and leads itself well to using a diffuser. But diffusers
have to direct light in the direction one wants and can impart an awful
color to the light.


Thomas
 
V

Victor Roberts

Jan 1, 1970
0
On Thu, 05 Jan 2006 08:21:49 +0000, Simon Waldman

[snip]
Just the tube. It is possible that you are already using a triphosphor
lamp though - check what it says on the tube. Depending on the
manufacturer, there will usually be a three-digit number - e.g. 830.
This refers to the colour.

The first digit refers to the colour rendering index. The higher this
is, the smoother the spectrum of light from the lamp, and so the less
distortion of colours. Triphosphor lamps will usually be Colour 8xx or
9xx, wheras older ones may be 6xx or may have a two-digit number (or no
number at all). There is a trade-off between the two triphosphor ranges
in that colour 9xx lamps, while providing better colours, usually
provide less light for the same input of electricity than the 8xx versions.

[snip]

I disagree that the higher the CRI the smoother the
spectrum. Old halophosphate fluorescent lamps had a very
smooth spectrum compared to tri-phosphor lamps, yet they
often had a CRI near or below 65, compared to a CRI of 80 to
90 for high quality tri-phosphor lamps.

CRI is a measure of the ability of a lamp (or more
correctly, the SPD of a lamp) to render colors accurately
compared to a blackbody at the same color temperature - at
least for CCTs below 5000K. (Special sources are used for
comparison at 5000K and higher.) To the best of my
knowledge, determination of CRI usually involves the use of
only 8 color samples, so it is possible for a "spiky" SPD to
have a high CRI while rendering some colors quite poorly.
This is one reason why the current method of determining CRI
is under attack and new methods are being proposed.

--
Vic Roberts
http://www.RobertsResearchInc.com
To reply via e-mail:
replace xxx with vdr in the Reply to: address
or use e-mail address listed at the Web site.

This information is provided for educational purposes only.
It may not be used in any publication or posted on any Web
site without written permission.
 
S

Simon Waldman

Jan 1, 1970
0
Victor said:
I disagree that the higher the CRI the smoother the
spectrum. Old halophosphate fluorescent lamps had a very
smooth spectrum compared to tri-phosphor lamps, yet they
often had a CRI near or below 65, compared to a CRI of 80 to
90 for high quality tri-phosphor lamps.

CRI is a measure of the ability of a lamp (or more
correctly, the SPD of a lamp) to render colors accurately
compared to a blackbody at the same color temperature

True. My apologies to all for a rather inaccurate and badly worded
explanation.
determination of CRI usually involves the use of
only 8 color samples, so it is possible for a "spiky" SPD to
have a high CRI while rendering some colors quite poorly.
This is one reason why the current method of determining CRI
is under attack and new methods are being proposed.

I didn't know that... interesting.
 
Z

Zak

Jan 1, 1970
0
RickR said:
Are you folks aware that CRI is a subjective value?

It should be. Lighting aids in perception of color; perception is
subjective.
My understanding of the proceedure is that a committee views <pastel
colors> and then votes it a CRI value.

I just read here that the test probbably needs adjusting, which sounds
reasonable. OTOH one can devise a test where any non-incandescent will
fail without reason. What usually matters is the rendering of actually
occurring colors, whether artificial or naturally occurring - limited to
indoor use.

I also wonder how much 'truth in advertising' there is.


Thomas
 
V

Victor Roberts

Jan 1, 1970
0
Are you folks aware that CRI is a subjective value?

My understanding of the proceedure is that a committee views <pastel
colors> and then votes it a CRI value.

If so the members of this committee must be very small and
able to live for years with no food or water since many
spectrophotometers can be used to determine CRI without any
additional human intervention :)

The CRI value is calculated. Others here have far more
expertise than I do in the measurement of CRI, but my
understanding is that it is based on the difference in color
between the test source and the reference source (at the
same color temperature) when each is used to illuminate the
8 test-color samples, though I believe that the actual
test-color samples are replaced by the now standardized
values of reflectivity vs wavelength for each test-sample.
To quote from the Handbook of the Illuminating Engineering
Society: "The indices are based on a general comparison of
the lengths of chromaticity-difference vectors in the 1964
uniform color space. The rating consists of a general index,
Ra, which is the mean of the special indices, Ri, for a set
of eight test-color samples that have been found adequate to
cover the hue circuit."

I agree that the eight test-color samples may have been
initially chosen by a committee. But once chosen and built
into the specification, the system of measurement is
mechanical and consistent.

--
Vic Roberts
http://www.RobertsResearchInc.com
To reply via e-mail:
replace xxx with vdr in the Reply to: address
or use e-mail address listed at the Web site.

This information is provided for educational purposes only.
It may not be used in any publication or posted on any Web
site without written permission.
 
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