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Wasp but what sort?
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P_T



Joined: 19 Jul 2008
Posts: 461
Location: Sydney, Australia

PostPosted: Thu Jul 31, 2008 6:35 pm    Post subject: Reply with quote

augusthouse wrote:
Laurie,
The 'cold' generally refers to the K temp. Flash is 'hot' because it has a higher K temp.

Visually, it is the opposite. A halogen has a visually warmer light and flash has a visually cooler light.

If someone can explain this in a more technical way - please do.

Craig
Is it something like how flame with blue colour is hotter than flame with yellow colour? That's how I remember this colour temperature thing.
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augusthouse



Joined: 16 Sep 2006
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Location: New South Wales Australia

PostPosted: Thu Jul 31, 2008 6:47 pm    Post subject: Reply with quote

P_T

This is one link I just found. Yep, it mentions the 'flame'.
http://www.apogeephoto.com/july2004/jaltengarten7_2004.shtml

Craig
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g4lab



Joined: 23 May 2008
Posts: 1434

PostPosted: Thu Jul 31, 2008 8:27 pm    Post subject: Reply with quote

As far as fiber optic lights are concerned you can't really generalize. There is wide variation in the 1)bulbs used, and conditions they are operated under2) the heat filters (and possibly color correction filters )which may be present to protect the fiber optic end and 3) the transmission spectrum of the fiber optic fibers themselves which may alter the spectrum of light going through them.

This often results in quartz halogen fiber optic illuminators being deficient in blue light.

Thank heaven for Auto White Balance.
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rjlittlefield
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Joined: 01 Aug 2006
Posts: 20286
Location: Richland, Washington State, USA

PostPosted: Thu Jul 31, 2008 10:33 pm    Post subject: Reply with quote

augusthouse wrote:
If someone can explain this in a more technical way - please do.

The big problem is a wonderful inconsistency in the language.

Much light is produced by very hot "black-body radiators" like incandescent filaments, combustion flames, and the sun. If you look at the light produced by such radiators, then "warmer" = redder light is produced by a source that is actually "cooler" = lower degrees Kelvin. Similarly, light that is "colder" = more blue is produced by a source that is actually "hotter" = higher degrees Kelvin.

Regardless of the actual temperature of the source, the light can be run through filters that modify its color balance to correspond to a source having some other temperature. Thus there are "warming" filters that make the light look as if it had come from a lower temperature source, and so on, retaining the inconsistency.

Adding to the confusion, the term "cool" or "cold" light is sometimes used to describe light that contains little or no infrared (IR). Such "cold light" can be produced in a variety of ways, either from intrinsically cool sources such as LEDs, or by filtering to remove the infrared from light produced by a hot radiator. Regardless of the mechanism, such "cold light" will raise the temperature of a subject much less than light of the same color and visible brightness coming directly from a black-body radiator. (This is because typical black-body radiators deliver something like 10 times more energy as infrared than they do as visible.)

Adding to the confusion, it's also common to describe the light coming from low-temperature sources as either "warm" or "cool" depending on its color. Thus you can have a "cold" (no IR) source producing light from very "warm" (reddish) to very "cool" (bluish)!

The bottom line is that you have to be clear whether the words are talking about the color of the light, the temperature of the radiator, or the amount of energy delivered to the subject as IR.

As g4lab says, it's dangerous to generalize about fiber optic illuminators. The unit that I use contains an IR filter, and I often run it far below normal operating temperature. Thus it delivers very little energy as IR so it is "cool" (but produces light that is very "warm" = reddish. Sigh...). Remove the filter, use a different bulb, run it all the way up, and the story could be very different.

I generally don't rely on auto white balance, by the way. It is much too vulnerable to being misled by colors in the specimen or background. Instead, I set custom balance from a white card placed in front of the specimen, after I have already determined the proper brightness setting to produce the exposure time I want. Changing the brightness setting also changes the filament temperature and thus the color balance, so it's important to set the balance last.

Hope this helps -- all this "temperature" stuff is a very confusing topic.

--Rik
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Harold Gough



Joined: 09 Mar 2008
Posts: 5787
Location: Reading, Berkshire, England

PostPosted: Thu Jul 31, 2008 11:25 pm    Post subject: Reply with quote

augusthouse wrote:
Laurie,
The 'cold' generally refers to the K temp. Flash is 'hot' because it has a higher K temp.

Visually, it is the opposite. A halogen has a visually warmer light and flash has a visually cooler light.

If someone can explain this in a more technical way - please do.

Craig


It depends, at least partly, on your flash unit. Those with gold reflectors warm the light up somewhat.

Harold
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Harold Gough



Joined: 09 Mar 2008
Posts: 5787
Location: Reading, Berkshire, England

PostPosted: Thu Jul 31, 2008 11:41 pm    Post subject: Reply with quote

g4lab wrote:
Quote:
I'd read somewhere about fibre optic lights being 'cold' and I'd assumed stupidly that they all were so. Apparently not, so something to watch out for!

When I was shopping for the M400 outfit in 1977, a swiss guy from Volpi USA (which was brand new then) kept telling me over and over "Its so cool you can put a chocolate under it and it won't melt"

That actually is not consistent with my subsequent experiences.
But I still like fiber optic illumination the best. You can put it right where you want it. And wide variety of guides and tips.

If you read old books on microscopy you will see a lot of lore about water cooling cells. Especially where arc lamps are involved.


I can tell you, from years of daily use with microscopes, that the (1970s?)Volpi, and other cold light fibre optic units used for microcope work, directed only a tiny fraction of the heat onto the subject that the Vickers intense lamps we were using in the 1960s did.

Harold
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