A look at a simple principle of stage lighting colour theory – reflected light. This article explains how coloured light interacts with sets and costumes and how to avoid errors when choosing saturated colour for your theatre lighting.
Why my blue LED torch is no good
I have a cheap keyring torch with a blue LED. It’s very bright and very handy – but it’s no good.
First time out, looking in a dark flightcase – realise that I can’t see what I am looking for. The stupid thing is, as a Lighting Designer, I should have known this already.
The reason that this medium blue (like primary blue light) LED is unhelpful, is it doesn’t let you see Red LX taped cables (in this case – 20 Metres ) or Green ones (10 M). This is basic lighting colour theory and is all about reflected light.
Object Colour and Lighting
The colour that an object – cable marker,costume, whatever, is the result of reflection of part of the visible light spectrum. A red object reflects the Red light, Green object/Green light etc.
You may know that the visible visible light spectrum is made up of a whole range of colours from violet to red. To simplify things a bit let’s forget about the 1000’s of different shades in the spectrum and break light down into the 3 primary light colours – Red, Green and Blue.
In this case, the colour that an object reflects is a combination of these primary lighting colours. The trouble with Red and Green LX tape is that it doesn’t reflect Blue light – like the LED in the torch. In fact, this mismatch of available light and reflected colour makes the tape markers seem to disappear. The Blue marked cables (5M) positively zing under the Blue LED torch light – you can think of the Blue light as an absence of Red and Green light, if you like.
Why white light reflects colours well.
Daylight, household light bulbs and camera flashes all produce their own version of white light. White light reflects different colours well, being made up of many different colours in the spectrum. This creates a situation where all the different coloured objects reflect their colour evenly – unlike using the blue LED torch.
What happens to reflected colour under the “wrong” light?
In theory, a primary green coloured object under primary red light turns black (it doesn’t reflect the available light). In practice, this usally means a severe distortion of the objects colour and a dead appearance, with little light reflected back to the eye. Wasted light.
This can happen with other lighting colours, as well as primary light. I recently saw an instance of a mid Blue backcloth being lit with an Amber gobo. If you know that Yellow is a secondary lighting colour, it can be created using Red and Green light mixed together, you might realise that the Blue backcloth is going to reflect very little of the Amber light shining on it.
How to use this knowledge in lighting design.
Understanding that some lighting colours reflect better on certain costumes and scenery means that you can make informed decisions when choosing colour. The paler colour gels in stage lighting emit a large proportion of the visible light spectrum, so they are not a problem. More saturated colours, particluarly the primary and secondary lighting filters, can have a dramatic effect on the reflected colours on stage.
If you want the heroines red dress to stand out, don’t light her in medium blue – if you want to find red marked cables in a roadbox, don’t use a bright blue LED torch.