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    “...Problem with RGB Lights”
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    Senior Member Bern Caughey's Avatar
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    ”Color Scientist Explains the Problem with RGB Lights”

    https://youtu.be/5U-F7EhLp7g


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    Pretty funny how these lighting manufacturers are advocating the use of gels when their "no more messing around with gels" was such a huge part of their marketing pitch in the early days.

    Can this problem be solved with lights that have an "eye dropper" function where you select part of an image and the light will recreate that colour?

    If the light achieves the same result by its own "mix" then I don't see why it should be much of an issue?


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    Senior Member Grug's Avatar
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    Great video. Frieder from Kino Flo does an EXCELLENT presentation on all this that he's toured around the world a bit, that clarified a lot of these spectral issues for me.

    The part I don't quite understand is why the LEDs that have enough spectrum for a good result with gels, can't simply limit that spectrum to a level that would match their gelled performance (as gels are only removing parts of the spectrum, not adding to them).

    I assume that it's because the LED emitters are a bit too blunt of an instrument for that, and when you reduce (for example) green, you're reducing all of your green, rather than just the specific portions that a particular gel could block.

    I do wonder though, whether reducing your green proportionally (so that some of your green emitters are lowered, but some remain pumping out their full spectral compliment) might help with that?
    Last edited by Grug; 10-08-2019 at 06:16 AM.


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    Senior Member paulears's Avatar
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    It's the interaction of gentle curves that is the key feature. If you look on the Lee Filter website you can see the spectral curve of all their filters and they are moderate to reasonably steep curves, so have an effect at the key frequency, but also have an impact either side, and some of course have very surprising chunks being filtered out that seem very odd to the actual colour we see. They produce a range of LED gel to produce the same colours as their tungsten range, and to the naked eye some of these are really, really strange to look at. No common sense works when you see the gel in daylight or tungsten and then see what a white LED light produces. Compare the gel spectral plots with LED plots with the spikes and sudden dives. If you overlay the different LED colours, it doesn't approach the curve of a real gel. Red and Blue LEDs can do amazing/horrible things with fruit (as I discovered recently) Blueberrys are totally black in red light and tomatoes and strawberries black in blue light. If you then fade in the wanted colour, they suddenly pop into life with just a tiny bit of the missing colour. Black strawberries and bright blueberries suddenly snap to red strawberries with a tiny fader prod. Not remotely gentle in terms of a fade in. In theatre we now have red, green, blue, amber, white and UV LEDs in a mixing wash light. None of these recreate the tungsten light from the fixture next door. Close, but not the same.

    It's a bit like those painting by numbers arts sets for beginners where you don't mix the colours, just use 22, or 43 next to each other - where that guy Bob in the painting series just slaps together a few colours and mixes them. A very different end result.


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    Can they make more affordable, LED specific gels that don't need to be heat resistant? How much of what you're paying for in a gel is the flame retardant? Maybe the price wouldn't come down that drastically regardless?
    Last edited by rob norton; 10-08-2019 at 11:46 PM.


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    Senior Member paulears's Avatar
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    Gel has never been cheap, and the price of LED gel reflects the quantities sold. It's a consumable anyway. As for flame retardant? They cannot control what people will do with it, and I've already got plenty mixed up with the ordinary stuff, so it all has to be safe. Nobody ever thinks about safety when hunting through rolls of the stuff for the perfect match, by eye. Most people write the colour on the corner, but it's always a good induction job for new people to give them the usual mess of gel and ask them to put it identical colour piles.

    What I do know is my gel purchases last year were 10% of what they were the year before because we have so many LED fixtures now.


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    Quote Originally Posted by paulears View Post
    Gel has never been cheap, and the price of LED gel reflects the quantities sold. It's a consumable anyway. As for flame retardant? They cannot control what people will do with it, and I've already got plenty mixed up with the ordinary stuff, so it all has to be safe. Nobody ever thinks about safety when hunting through rolls of the stuff for the perfect match, by eye. Most people write the colour on the corner, but it's always a good induction job for new people to give them the usual mess of gel and ask them to put it identical colour piles.

    What I do know is my gel purchases last year were 10% of what they were the year before because we have so many LED fixtures now.
    Yes you're right (just looked up lots of prices), filters aren't cheap either way. Not necessarily related but interstingly, the number of LEE colour effects filters drops off dramatically when you select the "High Temperature" option - http://www.leefilters.com/lighting/colour-list.html#.


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