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Physics: Color Temperature

Discussion in 'Lighting and Electrics' started by kingfisher1, May 16, 2006.

  1. kingfisher1

    kingfisher1 Active Member

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    Okay, i'm not very well educated on this whole color temperture thing but i feel thta i know the basics. so if i saying something stupid please please correct me.

    With that said, humans see white light as white because of color correctivivity in our eyes. white light can really actually be a reallly really bright blue, green, yellow, etc. SO, can white light physically be a really really bright black.

    Why NO! we all cry. How could the absense of light be infinatly bright? its inherently contradictory!

    well, we have heard of black light.... can we take black light to the extreme? have we already done that, and are now using it somewhere in science. I'd image it requires a heck of a lot of energy input.

    so, the human eye can't see UV light, but in technicality, ultra intense Uv light could infact be white?

    To answer this we might need to adress the definition of white light, or of electromagenetic waves in general. is white merely the resulant of of a certain wavelength?
     
  2. Radman

    Radman Well-Known Member

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    I'm not a theoretical physicist, but this doesn't really seem to have anything to do with color temperature. Wavelength and color temperature and brightness aren't really comprable, its like apples and oranges... and banannas.

    However, think of it this way: black is the lack of light, correct? True black at least means zero light is reflected or emitted. So there IS ZERO LIGHT. The absence of light is not a specific wavelength of a electromagnetic wave, it is the absence of any frequencies altogether. Pretend photons are beach balls, and the brighter the light is comparable to a greater number of beach balls. We have different colored beach balls to represent different wavelengths (colors) of light. Blue light is a blue beach ball, red light a red ball, and so on. Black however is not represented by a black beach ball. Black is the absence of beach balls. There are no black beach balls, so there can be no great number of black beach balls to be ultrabright blackness and perceived as white. There simply aren't any balls. There is no light. There is no way for nothing to be in great numbers therefore ultrabright. It's just, nothing.

    At least, that is how I understand it. Like I said, I'm no physicist.
     
  3. soundman1024

    soundman1024 Active Member

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    Color temperature is the temperature at which a light burns expressed in Kelvins. Kelvins is just another means to measure temperature like farenheight or celcius. Color temperature and color are different.
     
  4. soundman1024

    soundman1024 Active Member

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    I just found this by looking at a Wikipedia article.
    http://www.techmind.org/colour/coltemp.html
    The first image diagram there shows lines over a color spectrum. As you can see color temperatures are just different amounts of all colors.
     
  5. disc2slick

    disc2slick Active Member

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    I don't know if there is any truth to this but color temperature, or at least the reason why it is considered a temperature, and i measured in Kelvins (a measurement usually for hot/cold). You know that as something is heated it changes color, think of a bunson burner or gas flame. The hottest part of the flame, closest to the source is blue going then to orange and then red. Color temperature represents the degree kelvin to which a theoretical black mass would have to be heated to achieve that shade. Essentially, the hotter, or higher temperature it gets the "bluer" it gets.

    Do not, however, confuse this with hue. It is possible to put a blue gel in front of a light and have it still have low (warm) color temperature. Color temperature refers, generally, to the source of the light. Of course there are color correction gels (the Lee 200 series for instance) that are designed to raise or lower the color temperature of a light without adding a lot of color to it. Although in theater we don't usually think of them as color correction so much as just different shades of blue or orange (CTO and CTB are really more film/TV stuff).

    Did that make sense? I feel like I always ramble whenever I try to post.

    -Dan
     
  6. DarSax

    DarSax Active Member

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    I'm sorry, but whaaaaaaaaaaaaaaaaaaaaaat are you talking about? This topic makes ABSOLUTELY no sense.

    "Black light" is just a term for ultraviolet light. All visible light is, is an electromagnetic wave that our eyes can pick up on. Ultraviolet light is simply another electromagnetic wave with a wavelength too small for our eyes to interpret.

    And also, no. White light is not just the result of a certain wavelength, it is the blending of all wavelengths of visible light, from 560 to 780 nanometers. There is no wavelength measurement of "white" light; the color spectrum as you've always seen in rainbows, etc. is all that really exists.

    I haven't studied light physics in a while, or else I'd be better able to explain this. Basically, everything you said in your post is...wrong.

    Black, by the way, is simply the absence of light. You can't make a "bright" black like you can make a "bright" blue. That's like making a very dense vacuum. The fact that it's a vacuum means it has no density.
     
  7. Radman

    Radman Well-Known Member

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    I see now that I slightly missed what you were getting at with the black light (haha oxymoron) I assumed you were talking about "black" light not blaclkight UV. In rereading, I can tell you this: I have worked with some very powerful blacklights, and about the only thing that makes them appear remotely white is when you're looking at something white. Otherwise everything looks off and most anyone can pick up that it isn't white. Also note that blacklights are generally not entirely UV (perhaps not at all UV, I forget), they do have a little visible light at the end of what our eyes can see, so a pure UV light I doubt would be even visible. And yes white is all colors of light combined, not one wavelength. That is why a prism splits into those colors, roygbiv red orange yellow green blue indigo violet.
     
  8. Chris15

    Chris15 CBMod CB Mods Premium Member

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    UV light is beyond the visible spectrum for humans, but that does not mean that our bodies can't detect it - think sunburn. Every light source emits electro-magnetic radiation at all wavelengths. It just has a dominant wavelength. So all lights emit some UV, and for this reason, some lamps have UV filters.

    An interesting fact: The light spectrum really only contains 6 colours, Red, Orange, Yellow, Green, Blue & Violet. Indigo was added as a seventh colour by the church because of the association of the number six with the devil.
     
  9. jfitzpat

    jfitzpat Member

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    I think I get what you are asking. First, the basics. Visible light is electromagnetic radiation (EMR). So are radio 'waves'. It is a very broad spectrum and when we talk about different portions of it we generally differentiate by 'wave length' or 'frequency'.

    The human eye is sensitive to a small band of EMR wavelengths. There is no wavelength for 'white'. White is a human perception. When we detect uniformity across the tiny band of the EMR spectrum that our eyes can 'see', we interpret the uniformity as white. By nature, our brains compensate for modest inconsistancies. That is why lights on a stage can look 'white', until we turn on a fixture with a different color balance - then all the 'white' fixtures suddenly look, say, 'blue-ish'.

    Any apparent association between intensity and 'white-ness' is primarily due to the limitations of our eyes. As light gets dimmer it eventually reaches a point where our retinas can no longer reliably detect color. Most people then perceive light as a non-white color. Similiarly, as intensity increases our color sensing becomes saturated and we tend to perceive even fairly unbalanced (non uniform mix of wavelengths) as white.

    As noted, UV is not part of the visible spectrum (at least not for most of us, a very small number of people seem to have vision that spans a significantly broader portion of the EMR spectrum). So, no matter how bright you make it, it will never be seen as white. Though, again as noted, you can get a spectacular sun burn and retina damage (we don't 'see' it but it still can cause tissue damage, including the tissue in our eyes).

    -jjf
     

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