RGB LED Colourmatching

[back_ache]

It would see that LED is gaining a pace, but one thing that seems to be missing is a way to may the colour you get from one fixture to another for a given set of values.

 

I am thinking it would be nice to be able to mix and match your fixtures and know if your want to turn the room lavender you don't have to work with each type of light individually to be able to get them to all do the same thing!

 

I know because of the way LED works its unlikely to be anywhere near a perfect result , but I'm thinking it could be better than it is now and could be useful for comparing the gamut of fixtures.

 

What I think would be a good idea is if there was a central repository on the web for colour profiles that you or your console could grab from and the community could contribute too.

 

It seems such an obvious idea, I can't help but wonder if it has already been done?

[adam2]

Not viable IMHO, low end LED fixtures vary very significantly from batch to another, and sometimes from one example to another even if from the same shipment.

 

Even the cheap LED lanterns are getting brighter, so intensity as well as hue will vary according to when built even for nominally identical units.

 

 

 

LEDs are often the best option for deep saturated colours. For lighter or pastel shades LED may not be the optimum option, especially if accurate colour matching between units is required.

 

If LED sources are to be used for such purposes then if possible they should all be of the same make and age. Some variation is still likely, but with care it should be no worse than with halogen.

[timsabre]

Not viable IMHO, low end LED fixtures vary very significantly from batch to another, and sometimes from one example to another even if from the same shipment.

Even the cheap LED lanterns are getting brighter, so intensity as well as hue will vary according to when built even for nominally identical units.

LEDs are often the best option for deep saturated colours. For lighter or pastel shades LED may not be the optimum option, especially if accurate colour matching between units is required.

If LED sources are to be used for such purposes then if possible they should all be of the same make and age. Some variation is still likely, but with care it should be no worse than with halogen.

 

This is true for the very cheapest end of the market, but most other LED stuff (upwards from Chauvet and the like) use binned or ranked LEDs and have good colour consistency. The difference comes between different fixture manufacturers, and I think Back Ache's idea is a good one, but I don't think anyone has done it.

 

The difference in LED colour can mean that it's impossible to match the colours between different fixture types - for example the blue LED in Robe Cityskapes is much deeper blue than in Chauvet Colorado Tri Tours which have quite a greeny blue. If you want that deep purply blue colour (the nearest LED can get to congo blue), the Robes get much closer to it than the Chauvets which always look too "light", and you can never match them.

[bigclive]

The output of LEDs degrades over time, particularly with the gallium nitride technology (blue, green, white) so even if all fixtures were matched, all it would take is some applications that used saturated primaries for modest lengths of time to cause the fixture equivalent of "screen burn" and throw the matching off.

[ImagineerTom]

At various times over the past 10 years I've met people with pet projects that consisted of an optical sensor (everything from proper kit to simple CCD's) and a software algorithm that scrutinised the light actually produced relative to the DMX commands in and then worked out how to replicate that colour with different pieces of kit. Ultimately that's going to be the way to do it as the entire lighting world isn't going to agree on a standard 4-way set of precise colour temps for LED and other mixing technologies though I'd question how much of a problem this actually is - different shades of a single colour are an integral part of lighting design and the easy and availability of lighting fixtures is such that if you want 20 lights the exact same colour you'd just get 20 of the same light. I'm struggling to think of situations where having identical colours across different fixtures was essential but I can easily think of plenty of examples where different shades and tones were an important part of a design.

[indyld]

+1 for Tom's comments above.

 

One of the biggest issues facing control makers at the moments is making methods of picking colour meaningful in relation to the fixtures themselves, even discounting for the degradation that Clive mentions.

 

Some fixtures attempt to help out by having inbuilt colour selections based on an idealised set of values using their LED technology. Standard colour pickers (I loathe them as a means of setting colour mixing fixtures but anyway...) were simple and based on RGB screen values. These, of course, don't work with non-RGB systems and most notably things like the various ETC 7 colour LED systems. ETC's (and Carallon's) solution to this is to attempt to provide notional equivalent familiar Lee or Rosco swatch colours (via the fixture library) to be picked directly by the user. However, these are regularly a terrible match, not least because LED isn't tungsten and isn't going to be.

 

The issue with this way of providing pickable colours is that, unlike with an RGB system, a point on the CIE colour model can be arrived at using a variety of different mixes with completely different spectral makeup for a given diffuse hue as seen on a white reflector.

 

Slightly OT but I was discussing this with a couple of well known theatre LDs at World Stage Design yesterday: It's funny to consider that the first thing anyone does when being shown an LED colour mixing system is attempt to evaluate it's capabilities by asking for Lee 201!! The future of colour mixing equipment and methods of control is surely all the better for it's lack of uniformity across the fixture types?