On 05/01/2014 17:30, Vir Campestris wrote:
On 05/01/2014 09:30, MattyF wrote:
As I've discussed before, I wanted to make headlamps that can be quickly
switched from yellow to red when the vehicle reverses, and to run off a
car battery for many hours. So LEDs were the logical choice. But the
final effect has to look like a gas mantle.

The headlamp reflectors are two feet wide and the LEDs have to shine
towards the reflector, so a normal LED bulb is no good.
I decided to have 90 yellow LEDs and 30 red LEDS. Here they are, wound on
a copper heat sink (of course normally only one colour would be on at a
time):

http://i39.tinypic.com/9gbo90.jpg

Here's a finished lamp with a Teflon tube and nylon mesh around it to
diffuse the light:
http://i41.tinypic.com/1zx7hjs.jpg

Here are the copper and brass heatsinks:
http://i43.tinypic.com/2qno2ky.jpg

But the 90 yellow LEDs got a bit hot after 20 minutes, so I put a 12v 1.4
watt computer fan on the back and that cooled the LEDs down to barely
warm:
http://i39.tinypic.com/vynsxs.jpg

Here's the lamp without a diffuser. Looks a bit weird!
http://i43.tinypic.com/w9be6q.jpg

I put some 0.5mm Teflon around to diffuse the light.
http://i41.tinypic.com/2dl0i90.jpg

Here's the headlamp from the front:
http://i43.tinypic.com/so47rl.jpg Yellow

and switched to red:
http://i43.tinypic.com/2v9t8jn.jpg Red

Full steam ahead!

Don't want to worry you after all that work... but are you sure gas
mantles are that yellow? ISTR them as surprisingly white - more so than
a standard incandescent lamp. But it's many years since I saw one.

Andy

Gas mantles often had a pronounced greenish-tinged light. (They were
still using them on many Southern Region stations back when I was at
school in Surrey.)

--
Rod