At the Southampton Boat Show the Cruising Association did a demo of what happens when you put an LED bulb in a bicolour or tricolour light. I didn't actually see the demo, but in the past week I have spent many very slightly frustrating hours working with members of the Regulatory and Technical Services committee (RATS) trying to concoct a diagram which demonstrates what happens, for Cruising magazine.
Here is our current version:
From the starboard side, the light appears green - the tricolour is the correct shade, the bicolour definitely bluish. From the port side both lights appear to be the proper shade of red.
The frightening bit is the view from straight ahead. The tricolour appears, approximately, white. Through binoculars you can see that there is a green bit to starboard and red to port, but the effect is as if the coloured filters don't quite meet in the middle, which is not the case.
Apparently this is caused by two things, mainly:
- The light of an LED bulb comes from around its edges. The light of an old-fashioned filament bulb, with a vertical filament in this case, comes from the middle.
- There is no such thing as a white LED - it's a combination of yellow and blue light which our eyes see as white.