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Dual Color LED - Probably a dumb question!

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    Dual Color LED - Probably a dumb question!

    I'm in the market for some portable LED panels I can take in to relatively small spaces for filming some interviews. Think very small cafe or really small office.

    I've been looking at some that offer the ability to change the colour temperature, typically 3200 - 5500(ish).

    Now, I'm not expecting them to be dead nuts on, but let's say you walk in to an environment that is maybe 4500K...

    If you take a single colour LED source you can gel it (assuming you packed your gels) to get approx 4500K just like we've done with tungsten over the years.

    If you take the bi-colour LED panels that are made up of half 3200K and half 5500K it appears that they simply mix the two to give you an average 'look', but that doesn't seem to me to the be same thing. Am I wrong to think that now you have the worst of all worlds (as well as less potential light than all single colour that you gel)?

    You've effectively in a mixed lighting situation where you have some 5500K, some 4500k and some 3200K and now instead of having a matched lighting rig, 'nothing' will be right regardless of what you do with white balance.

    Am I missing something here?
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    #2
    The bi-color leds made of 1/2 warm and 1/2 cool leds come in 2 types. 1 is the type that has for example a 3 way switch that allows warm(3200K) only, cool(500K) only OR Both warm and cool that by their "mixing" give you that in between value of say 45ooK . If you need to have a slightly warmer or cooler than that 4500K ish tint, then you just have to apply a color correctiing gel or filter to get the temp. you require. You also have to put the ambient light color and intensity into consideration as that may also affect your final result even though you have achieved that 4122 K, you may get an undersirable result because you also may have "mixed" in the overhead fluorescents into the soup if they are bright enough to affect the color balance. The second type is the ones you can vary the intensity (dimming) of the warm and cool leds independently so you do not need the gels to obtain any temp between 3200 to 5500K. So in this case a slightly warmer from 5500K may just mean the 5500K leds dimmed down just a little with the warm leds dimmed up just a little. A single color "mix" control will do just that for you and is usually labeled as such. That control is independent from the main separate dimmer that controls BOTH sets of leds once the desired color is "dialed in". There are a few that do not have that main separate dimmer and you must "eye it" as you fumble with the 2 separate color knobs in order to get the proper dim level. The unit to look for is the one with a sepatate dimmer and color control knob, as most have it.

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      #3
      Thanks for the reply. Everything you said both makes sense, and was something I already knew. However, it's doesn't really answer my question.

      If I have both 3200K and 5500K leds emitting light equally, do I really have 4350K or do I still effectively have 3200K light and 5500K light as a mixed lighting situation? I'm guessing it's the latter, but if some one can show me I'm wrong then I'm happy to watch & listen.

      To put it another way, what's the difference between having daylight come through a window, using a tungsten light as a fill and then setting the camera to 4350K? It's not going to look right regardless of how you correct it later. What am I missing?
      Last edited by Exact; 11-11-2013, 12:53 PM.
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        #4
        When daylight is coming through the window, I fill with my daylight balanced LED, ad shut down all interior lights, especially fluorescents.
        This way it's all daylight and set my camera white balance as such.
        But there are times I need a little warmth on the person(s) faces , not much but just to take away the daylight a bit, then I gradually decrease the color temperature of the led to get exactly what I want.
        One always tends to balance out ( temperature wise) the entire scene to a particular temp . That is rarely the case even in movies. It all depends on the "look" you're after. Interior and ambient light that is also reflected off the colored walls also contribute to a color cast, and is almost impossible to get all the elements to your liking. We work in a given situation, we envision the outcome, we adjust and adapt to make it happen. In an ideal setup. yes. that would be easy, but sometimes even daylight varies in color from dawn to dusk by the hour. Filling with light to match it would be a constant battle. To answer your question, daylight from a window and tungsten fill will, depending on the brightness of your tungsten fill, vary in "warmth" . Sometimes setting the camera to 4350K may give undesirable results as 4350K may not be the exact resultant Kelvin but an estimated one that the camera will base it's correction at. A white card close to the talent with both light sources hitting it would be a good start for manually adjusting the white balance point.

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          #5
          Norman, thanks again for your reply.

          Again, this is stuff I already know and do myself (day light balancing, adding warmth etc etc), but not answering the question as such ;)

          Let me ask it another way.

          When the different led temperatures are evenly lit, do these appear to the camera as distinct 3200K and 5500K light sources (i.e. mixed lighting) or as a single 4350K light source?

          I know the human eye will see them as an average (4350K), but what does the camera see? We all know that cameras see light differently to the human eye.
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            #6
            Never mind - I ordered one and I'll do my own tests….
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              #7
              When you bounce an HMI and a tungsten light off a piece of bead board, you don't get something that looks like two separate light sources just because there are two color temperatures involved. Same with LED's, both color temperature LEDs are in just about the same position, it isn't going to magically look like two lights.

              One thing to consider though is that when you are mixing the warm and cool LEDs, you may need some very light plus green. Do tests, as with everything, but don't be surprised if you find you need to add green when you blend them (this is due to them not following the Planck curve, which veers towards green in between 3200 and 5600).

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                #8
                When you bounce an HMI and a tungsten light off a piece of bead board, you don't get something that looks like two separate light sources just because there are two color temperatures involved


                Correct, but if you point them directly at the subject instead of bouncing, now what?


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                  #9
                  Originally posted by Exact View Post
                  Correct, but if you point them directly at the subject instead of bouncing, now what?


                  [/COLOR]
                  If they were close enough together and far enough from the subject, nothing. They'd still blend together to work as one source, just as bicolor LED panels do.

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                    #10
                    Thanks, I guess that's what I've been looking for.
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