Bernie G4HJW recently posted to the UK Nanowave Yahoo about some powerful red LEDs that he bought from China for just £2.80. A couple of these are more powerful than the 10mm LEDs that I used in non line of night tests (when I was fitter) but even without any lenses! It would seem these would be ideal for optical tests. 50W is a lot of power. This was Bernie's post. I trust he won't mind me sharing it with you all:
"Morning all - This might be of general interest:
bought a couple of 50W red LEDs from China, which I thought I might use
in a wide-angle initial set-up lantern for portable use. They were very
cheap (£2.80), so I also expected there would be dead segments, which
there were, but there was a bigger surprise waiting to show itself.
this weeks UK uwave group net, Martyn G3UKV asked me how wide the
spectrum was, so out came my trusty secondary school Spectroscope.
Instead of the expected relatively narrow response, there was noticeable
output right through to yellow plus a weakish narrow line at the violet
end. This should have been an obvious clue, of course, but it was only
later when I was telling Stuart G8CYW (sorry about all the name
dropping..) that he suggested that the LEDs might be fluorescent driven
devices, just like the white lighting LEDs all seem to be these days.
He was correct, as the following picture shows:
that in pealing back some of the fluorescent gell, all but one of the
individual 1W UV leds have been destroyed. Not obvious from the picture
is that these LEDs are embedded in an initial clear silicon rubber prior
to the red fluorescent layer being applied. From supplier ebay
pictures, it is now clear that the same UV driven devices are available
in all colours, leading to the question - does this produce an overall
increase in efficiency, or is there simply a significant cost saving in
just fabricting UV LEDs?.
I've yet to measure the response time of the fluorescent material.
Working with simple optical gear was one of my great pleasures, so I very much hope I can do this again. Optical gear is easier than microwaves. All my kit was home designed and built and the test gear simplicity itself. For details of my optical work see http://www.g3xbm.co.uk . G4HJW and others know far more than me in this area. I consider myself very much a novice in this area.