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  #1  
Old 29th August 2020, 08:03 PM
Nat Polton Nat Polton is offline
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Default Enlarger Lamp Colour Temperature.

What should the colour temperature output be for a lamp used in a Durst Colour Head?
A neighbour gave me a couple of Osram Xenophot 64627 HLX EFP Lamps.
12v 100watt.
I looked them up on an Osram site, and it says " Maximum colour temperature 3200k."
On the box it says HALOGEN DISPLAY/OPTIC LAMP.
The website technical information says now using Xenon gas instead.

Ideal colour temperature for the lamp please?

Cheers.
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Old 30th August 2020, 09:14 AM
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Halogen enlarger lamps are nominally around 3200k - this (not by coincidence) is the same as a standard tungsten lamp bulb.

The gas used is largely irrelevant as far as I know - it just needs to be inert. Do they say why the switch to xenon?



[Edit: ok, answered my own question with the help of Mr Google: xenon makes the light slightly whiter and slightly brighter than otherwise (but not to be confused with HID xenon lamps which are discharge lamps). Bottom line: the colour temperature looks right.]

Last edited by Bob; 30th August 2020 at 09:26 AM.
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Old 30th August 2020, 04:25 PM
JOReynolds JOReynolds is offline
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Quote:
Originally Posted by Bob View Post
Halogen enlarger lamps are nominally around 3200k - this (not by coincidence) is the same as a standard tungsten lamp bulb.
Standard domestic coiled-coil tungsten lamps with a lifespan of around 1000 hours have a colour temperature (CT) of about 2950K (K as in Kelvin). Typical enlarger lamps, studio lamps and those built into reflectors have a CT of about 3200K and last for typically 100 hours, although halogen and xenon filling extends this. 'T' rated (tungsten) reversal film assumes 3200K for correct colour balance. Photoflood lamps, which have a lifespan of probably less than 12 hours, have a CT of 3400K and give a lot of light for the wattage but give bluish light on T film.
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Old 30th August 2020, 04:40 PM
JOReynolds JOReynolds is offline
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Quote:
Originally Posted by Nat Polton View Post
On the box it says HALOGEN DISPLAY/OPTIC LAMP.
The website technical information says now using Xenon gas instead.
Remembering back to the sixties, Tungsten-Iodine lamps (also 'Quartz') began to appear, but they had a pinkish cast. Later, a blend of halogens was used for the same purpose - to prevent tungsten evaporated from the filament being deposited on the inside of the envelope. This was set close to the filament to get hot and encourage the 'halogen cycle'. It extended the filament life. They also found a glass replacement for the quartz envelope. It's bit a bit magic, really, funded by suppliers to the motor trade because the technology was used in vast quantities in headlamp bulbs.
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Old 30th August 2020, 07:29 PM
Nat Polton Nat Polton is offline
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Thank you gents.

I shall now do the usual thing of putting them away safely for future use, and when the time comes to use them wonder where the heck did I put those lamps.
Cheers.
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Old 30th August 2020, 09:19 PM
John King John King is offline
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Default Colour Temp

Are we being to finicky about the colour temperature of the bulb in an enlarger. I have a screw fit LED bulb which I use in my darkroom to judge colour balance with RA4 prints and another identical one in an enlarger. They are 15w but give the output of a 75w bulb

Both are 6500 degrees Kelvin and I have not noticed any difference when printing B&W with below the lens Ilford Multigrade Filters except the printing times are a lot shorter. Typically 35s @F8, when printing 35mm to 12x16. With a normal darkroom bulb, it is usually closer to 60 to 70+ seconds.
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Old 31st August 2020, 12:19 PM
Nat Polton Nat Polton is offline
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Hello John.
When I started on colour in 1982 (purely amateur) a few of the books I read made an emphasis on stabilised transformers and using the correct bulbs. I think it was to do with repeatability of results for future reprints.
I didn't get into the science or technicalities. I just wanted good prints.

https://www.youtube.com/watch?v=-H5kuE5AGqg

The Naked Photographer on Youtube touches on the subject of enlarger light temperature in his video.

Link above.

In the questions a chap named Anthony Weekes mentions using 6500k temperature lamps.
The answer given is it may possibly lead to too high a contrast due to the extra blue from the bulb.

The following question answer mentions that paper is attuned to 3400k.

To my non too technical mind, it looks like there is a contribution from the temperature of the light source. Just as in daylight and tungsten light sources.
Shame there is no mention about using colour papers.

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Old 1st September 2020, 04:01 PM
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I'm not sure the bulbs colour temperature is particularly important - as long as you choose one temperature and stick to it.

With increased colour temperature you get a greater output of blue light - which will mean you get typically harder prints - I just don't know how much harder they will be - perhaps as much as a grade harder.

However, unless you are already printing most of your stuff at G00/0/0.5 this isn't likely to be a problem.

However, changing your bulb temperature or type will invalidate all of your previous printing notes - so you will have to start again.

If you are printing at the very softest of the grade range you probably have bigger problems with your film development time/temperature/agitation that you need to address first.

Martin
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Old 2nd September 2020, 11:38 AM
Alan Clark Alan Clark is offline
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Quote:
Originally Posted by John King View Post
Are we being to finicky about the colour temperature of the bulb in an enlarger. I have a screw fit LED bulb which I use in my darkroom to judge colour balance with RA4 prints and another identical one in an enlarger. They are 15w but give the output of a 75w bulb

Both are 6500 degrees Kelvin and I have not noticed any difference when printing B&W with below the lens Ilford Multigrade Filters except the printing times are a lot shorter. Typically 35s @F8, when printing 35mm to 12x16. With a normal darkroom bulb, it is usually closer to 60 to 70+ seconds.
John, I am intrigued that your 6500K LED gives the same results as a normal enlarger bulb, which would be around 3000K. If you print a "normal" negative at all the grades from 00 to 5 (or at least each full grade), for the same time, is there a change of contrast for the full range? And, most important, which tonal area of the print stays the same through all the grades, when the same exposure time is used throughout?

Alan
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Old 2nd September 2020, 11:46 AM
Alan Clark Alan Clark is offline
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John, I should have said "the same time up to grade 3.5, then double the time up to 5"

Alan
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