Red and white LED lights

You can get interior lights for boats that have a choice of white or red LEDs in one fitting. The red is used to preserve night vision. Perhaps you could adapt one of those.

Colin Bignell

What are you trying to do?

Heatsinking requirements might be a bit of a challenge to run the thing at the focus of a parabolic mirror. Cassegrain optics with a sperical mirror at the focus and the highly directional lighting assembly sat behind the mirror might be a much better engineering solution.

You can variously buy RGB, White, and individual coloured power LEDs to

LEDs take a voltage determined by their colour and must have a series resistor to limit the current from a battery. Although you can buy "12v" LEDs they are really 2-4v LEDs in series with a current limiter.

You can also buy clusters of red, yellow and green LEDs intended for traffic lights and similar but they tend to be more expensive.

Sometimes one of the radio ham shops has a better deal. I have made various physics demos of light mixing using these diodes. Do not look directly at them as they are close to eye damaging surface brightness.

It is better to either run 3 or 4 in series together with a current limiting resistor. If you only need two colours then DC polarity with a series diode to protect the LEDs from reverse voltage should do it.

There is a way to do voltage stepdown & current limit more efficiently used in commercial products but that is probably too complicated.

I assume this is a front/rear light for a tram...

Some cars/buses have light clusters with tail and reversing LEDs in the same cluster. I wonder if there's a generic version of those?

There are also 'tricolour' lights for boats (white/red/green) - they're made to show different colours to different angles, but perhaps you could abuse one of them.

Theo

These are quite cheap:

I'll have a look at automotive shops too.

There's already a lovely red light on one end, but half the time that would be facing forwards, so we have to shut the door:

FWIW British Southern Railway electric trains had no tail lamps. Instead they used the white two digit route code blind. If it was at the rear of the train a red blank was shown and it functioned as a rear indicator:

Theo

You made me pinch myself there. Then memory started to work a bit better. In the sixties, at least, you would see staff wandering around Guildford station with loads of oil lamps. I am pretty sure that even if they had the route indicator on red, they also used oil lamps. Maybe that changed later?

The effect that I want is to have an 18 inch wide red light for ten minutes and then an 18 inch red light for ten minutes. I could run around with a r ed filter as I've been doing, but I want to just switch the red or white li ghts on. There is one large reflector at each end of the vehicle. I want LE Ds pointing backwards into the reflector. The best effect would be to have about 30 alternate red and white LEDs with a diffuser over the whole lot. I 'd rather not have say 10 red LEDs together because I want an even spread o f light.

Search for "colour changing led" - there are lots and lots. Might be able to, ahem, adjust operation of the remote to only choose red and white.

Well, one of the UK's main suppliers to the industry has these:

but they are 24 V, and I guess that by the time they reached you would have cost a fortune.

Chris

Have a look at ....

Thomas Prufer

Check Ebay for Colour Changing Floodlight 12V

Example

The led element itself will be held into the housing with a couple of screws. If you remount it be sure to attach it to a substantial heat sink

The floodlight comes with a remote control