store bought LED string...

[xmastree]

Erm, no. I have packs of 5v Blue LED's at home which I usually wire into PC's by wiring them direct to the Red/Ground cables from the PSU molex connectors

I'll bet they have a built-in resistor...

[slaveofconvention]

Not that I can see... Admittedly, this is a 4.5v supply, but still hugely enough to blow a 1 or 1.5v led....

[xmastree]

Nice picture, it's always hard to photograph a light source. I'd be interested to see how much current that's drawing. Better still, hook it up to the 5V in the computer and measure it.

Anyway, a blue LED will never be 1.5V, IIRC only red ones are that low.

As for 5V LED's...
http://led.linear1.org/myth-of-the-5-volt-led/
In particular, this paragraph:

The specs on LEDs often include a reverse voltage spec, and 5V is not an uncommon value to see for this. But this is not an operating voltage, this is the maximum reverse bias voltage you can apply before the LED fails. This sort of confusion accounts for most of the “sightings” of 5V LEDs in the wild.

[slaveofconvention]

Does 17mA sound reasonable? I really don't know what I'm doing with a multimeter other than to test continuity but with it set at the 20m mark on the A section the reading hovers between 16.7 and 17 when wired in series with the LED - ie Battery - Multimeter - LED - Battery...

[xmastree]

Does 17mA sound reasonable?

Sounds fine. Is that from the batteries or the computer PSU?

Might be worth trying both and comparing results.

[slaveofconvention]

Batteries - was a quick 2 min test before I came to work this morning. As a side note - the batteries were pushing out 4.7v total - but I did replace them with brand new ones before I did any of this.

That link you posted - the page is nearly 4 years old I think - may well just be out of date as that LED is definitely handling a forward DC voltage of 4.7 - I'm betting that the information is just old and LED technology, like everything else, has just moved on a bit....

[Mark_Hardware]

I know this is late, but all you need to convert AC current to DC is a rectifier right? A diode...

[xmastree]

I know this is late, but all you need to convert AC current to DC is a rectifier right? A diode...

Well, yes, but if you want smooth DC you'll need a capacitor across the DC.

http://en.wikipedia.org/wiki/Rectifi...tput_smoothing