The main light source used in a theatre is tungsten. Theatre lamps range from 500w to 2kw and would be patched in to dimmer packs in order to alter the intensity of the lanterns.
Becoming increasingly common in the theatre are LED fixtures. These provide the user with a range of colours within the unit whilst having good side effects – they are very cost effective to run and do not emit any heat. Great for nightclubs and places where you want to keep the heat down. They have not yet become a lighting “must-have” however, as there are a few down-sides to them. The LEDs have a narrow angle meaning you must either use lots of them to light the stage or add diffuser which restricts the amount of light given off. Some cheaper fixtures’ power supply actually uses more than a tungsten lamp and people feel they cannot get the right colour from RGB LEDs and that certain hues cannot be mixed – warm oranges, cool blues, some people feel the colours from RGB are just too saturated.
This is why one company in particular, Martin lighting have introduced RGBAW, Red, Green, Blue, Amber and White. The amber and white allows a larger range of hues to be mixed but this can be fiddly and the lighting designers of today would find it easier to rig extra lanterns with gels they are familiar with.
Tungsten changes colour temperature as you dim it whereas LEDs do not. They simply change intensity. Therefore, with tungsten, as you dim it in a theatre context, you get the feeling of the light closing down. LEDs do not have this effect. However, for this project, this does not matter; the candles would not have been dimmed (although later on, lighting designer Sabbatini did develop this) and it means that the light intensity can be changed to match the intensity of the candles without losing the colour.
When I originally began the project, I want to use a mixture of LED and tungsten, and a 650w tungsten lamp dimmed to 40 % certainly has the appearance of candle-light. This would make it easier to gain the coverage that I needed across the stage whilst using chandeliers and footlights with the LEDs. However, I thought I would take the challenge and do it solely by LED…
To gain a true metamer of a colour, it needs to match the spectrum of the original colour in such a way that it will look the same in all spaces. For example, if I match my tallow candle using LEDs and I use amber and green, it may match perfectly in a black box space reflected on to a white background. However, if i then move that and put it in to a room with red furniture and blue walls, the amber and the green will not reflect the blue or the red in the same way the candle does because of the spectral qualities of the candle. A candle does not have a single peak at, say, 590nm, it is made up of probably every colour, spanning the spectrum. LEDs are not like this. They are monochromatic meaning they do have peaks. This makes it more difficult to match the range of colours needed.
This diagram shows the peaks of using filters and LEDs. As you can see, the filters have wider bands than the LEDs and are also much brighter – especially the green and red.
(Taken from powerelectronics)
The white LED has a wider spectrum range than the other LEDs so this may prove useful in my project.
The Arduino Diecimila board
This is a great little board I found that can be programmed using C++ code. The code itself is a little tricky to get your head around but there is lots of info out there on the web to help you. I found the Arduino homepage and forums useful and also a site called ladyada which has a great way of talking you through even the basics of setting up and using a board like this. It assumes you know nothing so means you get it right and begin to understand what you are doing too.
To view the code for my latest project, a colour matching device with 4 LEDs, 4 potentiometers and a function that sends the data to the computer, see under the heading “projects“.