This I understand. My question was how then is it transfered to us using colour temperature?

Grazie

Lets see if I can get this right. The color temperature refers to the spectral emission of an ideal black body at that temperature. It's roughly the same as the temperature of the object emitting the light, the lower the temperature the less blue , the higher the more blue.

So a candle flame is around 1,000 K, the surface of the sun roughly 5,600K.
Notable exceptions are gases and metal vapors at low pressure. The model is also imprecise as it doesn't tell you the whole picture. Two light sources may have the same color temperature yet have quite different spectral emissions, fluro lamps are a real trap.

Also you need a bit more info if you're trying to do CC or gel lights. There's no way you'll get a proper WB off candle light, there's just nothing at the blue end. Halogens on the other hand a down a bit at the blue end but you can compensate with a blue gel to knock the red end down.

Hope this helps.

Grazie, with the new cameras and auto WB, it isn't really too much of an issue, under normal circumstances. So there really isn't much that you'll have to "apply" in the work you're doing. This was, and still for that matter, of far greater importance when using film--motion picture or still.

The lower the number the "warmer" (more red/orange) the light will be. The higher the number the "cooler" (more blue/white) the light will be. For example, if you set your WB for "sun" and shoot in the early morning or late afternoon, or inside the scene will have a "warm" (red/orange) cast. If you set the WB for "incandescent lights" (lamps) and shoot outside it will have a "cool" blue cast.

What is your particular concern?

J--

Grazie, first of all,from a Canadian, thanks for spelling "colour" properly :-)

farss pretty much nailed it as far as definitions go.

What I found with a quick google search was:
"Kelvin, as it applies to colour temperature does not measure the temperature of the light-emitting filament but refers to the observed colour of a theoretical black body at that temperature."

Some links on this for you are as follows. HTH.
http://www.jasonelias.com/article%20color%20temp.html
http://www.3drender.com/glossary/colortemp.htm
http://www.cybercollege.com/tvp028.htm
http://www.tvtechnology.com/features/Tech-Corner/f-rh-white.shtml

Happy reading.

Degrees Celsius + 273 = Degrees Kelvin

Thanks VC and farss.

I know that the higher I go: red >> white heat : the Higher the temp. The hight the dgrees Celcius [ likewise kelvins ]. My concern is understanding where and how this all fits in with "cooler" colours like blue, having a high Kelvin value and warmer colours like red having a lower Kelvin value. Appears to me as a contradiction - but that isn't a new experience for me. ;-)

I also understand that with or without this closing of this part of my knowledge circle, that it will not stop me filming, but I do like to mop up the unknowns for myself - notwithstanding the patience given here and assistance I garner from you guys!

So, higher kelvin numbers, cooler colours. Warmer colours lower kelvin numbers. BUT when I use thermocouples the warmer the "colour" the higher the celcius number - the cooler the colour the lower the celcius number. This is true until I reach "white" heat where the celcius numbers get very large. I was wanting to know - historically - where and how this Kelvin arrangemnt raised its head? Something to do with photography? Something to do with . .. what exactly?

Still a tad confused .. . Grazie . .

P.S : I'm not purposefully being obdurate - promise .. just plain simple innocent wonder at trying to understand how this all fits together and who, where and how historically it came together for photography/film/videography . . . etc etc .. .

rs170a - thanks for that, I'll read on. Your, "Kelvin, as it applies to colour temperature does not measure the temperature of the light-emitting filament but refers to the observed colour of a theoretical black body at that temperature." is really taking some time to "swallow" = understand. The "Colour" is also the French way? Believe you too havce a French influence in Canada? N'est pas? ;-)

Musicvid - yeah, did know this - absolute zero being -273ºc or 0ºk.

Still trying to reconcile the history and photographic bit . .. .

Grazie

Well, the bottom line is that Kelvin and Celcius are not connected in any way, and shouldn't be (don't try this at home, kind'a thing), you might get burned! ;o)

It's like f-stops. The "higher" (bigger) the number, the "smaller" the opening. For example, f2.8 is a small number, but a large opening, whereas f22 is a large number, but a small opening.

J--

I also learned a new word today---"obdurate".

JJK

Oh, boy. Don't get into F-stops too!

Grazie, as light moves up from red to blue it becomes more energetic/higher frequency. You can use that as a conceptual handle here: bluer light = higher energy = higher temp.

Your thermocouples aren't "black" bodies and don't really count as a way to measure color (sorry about the dearth of letters there, we try to conserve here in the states. I'm saving them up for a really big word later)

I had always assumed that the color temperature scale was derived from an actual test material that emitted light as it was heated. Probaby foolish on my part. But, even though it's "theoretical" just remember that theory is pretty damned close to "Fact". When people talk about theories being vague they really mean "hypothesis".

Even with lowly video there are reasons to know about f-stops and color temperatures. The most obvious that comes to mind is when I light up a stage for a conference. It's rare that the camera is there on the pre-light day. In these cases I walk the stage with a meter or I use a spot meter on the scenic elements. You have to do the later from the camera positions because reflected light reflects to some places more than others (think about light reflection the next time you play pool-the ball bounces in a specific and predictable direction)

For color temp, I'd use a meter on Kinos and HMIs. HMIs are the most likely to be mismatched. However, I have to admit that I sold my color meter after moving off into postproduction and web work. I just don't need an $800.00 meter hanging around any more.

Rob Mack

Well in my experience you have to let the warmer colors, cooler cooler colors thing go away and treat it like a sort of diy interior decorating description rather than a video thing. I always ask people if they say they want something "warmer" exactly what they mean. Many people think that warmer means a higher color temperature. I treat color temp just as a color thing not a heat thing as otherwise i find it very contradictory too. For instance, a sunny day might be 5600 K whereas I've measured a shadow in the early evening or an overcast day as 9000 K. It just means that the shadow/overcast will make your video blueish just like metal goes blue hot at that temp I think. Similarly, early sunrise or sunset make your video yellowish. What is really amazing to me is that our eyes are able to constantly adjust for the different color temps.

Grazie, there was a great "Horizon" program years ago in the U.K. called "Colourful Notions' I think that was all about how we perceive colour(color). In the U.S. the show was called "Nova".

Regards...

Al

Whole books have been written on color theory, which is really what's being discussed. On top of the so-called color temperature one should have a basic understanding of how HUMANS preceive color.

Color Temperature has more to do with how colors become effected (as far as being preceived) depending on the intensity of light hitting them. We all know a person's skin tones viewed in candle light is much darker than the same person viewed outdoors at high noon on a bright summer day.

Lumiance or brightness of colors is also effected by where in the color spectrum a "color" falls. The human eye is construced in such a way so we are more sensentive to greens. Did you know that?

This is seen in Hue discrimination. In other words its more difficult to detect a change in hue for blues and reds with a proportionally larger change in wavelength being required to detect it.

Gets very technical, but interesting:

http://webvision.med.utah.edu/KallColor.html

C'mon guys please start converging this for me!

I like the Red low energy [ and as it happens long wavelength ]; Blue higher energy [ and yes a shorter wavelength ] . Are we onto something here?

So, the Kelvin Absolute scale of "temp" is really measuring "energy" and that we use this scale to determine where along this scale our beloved colours lie? This I can understand. Whether materials glow with whatever colour when "heated" aint the thing. After all materials will only glow a certain way when they are in a certain atmosphere. Give them a vacuum and another glowing colour will be shown. Now think about Neon gas . .yeah?

So, the Kelvin Scale is a type of "Holy Grail"of scaling colours. You are that colour whethter in a vacuum or on the Earth or on the Moon or where ever you may be - you are .. . er . . BLUE! and you have a Kelvin value of . . .. . Is this it people?

Nearly . . I think ..

BB, thanks for the introduction of Coloutr Theory . . and our eye's perception and training [?] in what we think we see . . yeah .. .

Grazie

Hi G, not one of my well learned topic, but as stated above, cooler = red, Hotter = Blue.
Now think of light in electromagnetic waves,
low frequency = Infra-Red (cooler),
other end Blue (ultra violet, hotter),
the higher the frequency the more energetic it must be, think of atoms vibrating.

Have a look at this from the "Society of Television Lighting Directors"
http://stld.org.uk/php/index.php?sectionid=22&parentid=6&contentid=52

Good to see you and your camera last Thursday...

Remember a line in one of the first Asterix books (Asterix and Cleopatra it was):I usually quote in such cases:
"Il ne faut pas chercher comprendre tout!"
;-)

Cheemie, yeah, I guess this is getting close. Thanks for the links. I'm amazed how many videographers bandy these figures and scales about without "knowing" from whence they come? Yeah?

AlexB - "Il ne faut pas chercher comprendre tout!" - 'It is not necessary to understand everything?' - Is that correct? Or are you saying that I should not keep hastling this and . . .what? Sorry Chum . . .I want to understand and I want to see how this fits together. This is the nature of me . . ..

Best regards,

Grazie

One has to keep in mind that an object at a specific temperature doesn't radiate a single color. Theoretically all objects radiate at all frequencies to some extent. However, a body's radiation spectrum will peak at one specific color corresponding to it's temperature. It's radiation will fall off gradually over longer wavelengths (cooler/redder colors) and very sharply at shorter wavelengths (hotter, bluer colors). As the temperature rises, the color distribution will center around shorter wavelengths. Eventually the temperature will result in a peak in the dull red range. It will radiate negligible amounts in the higher colors and it's radiation in the lower colors is invisible to us since it will be infrared. This happens at about 1000°K or so. As the temperature continues to rise the peak frequency will move through the visible spectrum going through orange, yellow, green, blue, violet, etc. Since the spectrum falloff is very gradual below the peak, there is still a substantial amount of these colors mixed in. By the time the temperature reaches 5600°K there is radiation through most of the visible spectrum and all these wavelengths mixed together appear white to us. It's not truly white because it's mostly green/yellow, but this is what we are used to seeing from the sun so it seems normal to us. At higher temperatures the peak moves beyond violet to ultraviolet, yet still retains diminishing amounts of lower frequencies, so the reddish colors dim more than yellow, which dims more than green, etc.

So, at no time does the temperature show a single color, but rather determines the overall mix of colors. Lower temperatures are predominately red with almost no blue. Higher temperatures are predominantly blue while still maintaining some amount of the other colors. In all cases the radiation is spread out over a broad spectrum including colors of enormous numbers of different frequencies mixed together.

Now, an important thing to remember is that all this only relates to incandescence, which is radiation of photons from electrons falling back into lower orbits after being excited into higher orbits by heat. (In simpler terms, burning something or heating a light bulb filament with electricity). There are other ways of producting light. The second most common method is fluorescence. This is light produced by excitation other than heat and doesn't follow the temperature scale at all. Different substances will radiate colors in specific frequences or sets of frequencies depending on the electron distribution in the outer shells of the atoms. Many substances fluoresce at only a single frequency and therefore show only a single color. Neon is the classic example with it's characteristic red/orange color. (And no, lights of other colors are NOT Neon!) The most common fluorescent light tubes radiate mostly in green and magenta colors that mixed together appear more or less white. These colors seem white to use because our retinas sense them as being at opposite sides of the color wheel so they complement each other. Other image sensors (CCDs, silver molecules) respond to colors differently and don't "see" those colors as complementary so they show a strong color cast under fluorescent lights.

Anyway, very long ramble. Hope it helps a bit somewhere and somehow. ;)

>My concern is understanding where and how this all fits in with "cooler" colours like blue, having a high Kelvin value and warmer colours like red having a lower Kelvin value.

I haven't read all the other responses and maybe you have it worked out by now, but I thought I would comment on this sentence you posted.

It's apples and oranges. You are confusing science with emotion in your statement. Blue is only a cool color (*u* -there's the extra letter if you want to use it) because we humans associate it with cool things like ice, and clear skys, and clear water, and night.

In the scientific world blue is on the hot side of visible light. The higher the temperature, the higher the average frequency of the electomagnetic waves emitted by an object.

You've seen the police helicopter pictures where they find the bad guy because of the infrared cameras seeing his image due to body heat. Throw some red hot coals out there and we can start to see the light with our eyes.

Put white light through a prism and it is split according to the frequencies of its radiations. Red (the low frequency, low temp) on one end and violet (the high frequency, high temp) on the other. If you go beyond what we can see you get ultraviolet, etc. The pneumonic ROY G BIV gives the order of the spectrum from cooler to hotter: Red Orange Yellow Green Blue Indigo Violet.

Turn on a tungsten bulb and it will have some general color depending on many things including how much electricity is forced through it. For normal illumination sources (a laser is an exception) there will be lots of frequencies of radiated emmissions, but their distribution will tend to be in a bell curve shape. As you heat or cool the source the center frequency of the most intense emissions will go up or down.

Others have probably said the same things. I just wanted to point out that blue is only cool in our emotional reaction to it, not from a light source where it would be very hot.

Kellsie, great stuff. Much to ingest here. However I think I can get an handle on it so that I can "see" how all this fits together, around the Kelvin scale.

RexA, good points you make - understood. Thank you for taking the time to read my post/s. Oh yes colours and their emotional descriptions can get in the way . . .

Thanks Guys, you are very helpful - Grazie

If you want to get into the physics of it a bit more, as the wavelebgth of electromagnetic radiation gets shorter (ie higher frequency) then the energy increases and in general its potential for harm to living things.
At higher temperatures the electrons make higher energy transistions emitting shorter wavelengths, if you keep pushing the energy up you go from blue light to UV, to xrays to gamma rays.

Thanks farss . . Yeah I did know this too. Actually most of what has been pointed out/back to me I've had trundling around my brain. It was the comments from Zcheema and Kelly that enabled me to "bring" together the Kelvin/wavelength/energy thing for videographers that made the difference for me. It was my need to see and understand how this all fitted together that was my quest. A little knowledge is very embarrassing.

Once again, Pals, you've really come up . . .trumps? - Anybody for a Rubber of Bridge? Which convention?

Be lucky,

Grazie___________________________________________________