by potholer » Mar 29, 2006 11:29 am
I made some on the suggestion of a friend last year, who'd been impressed by seeing them in use when he was over in Mexico some years ago.
I used cheap superbright red LEDs (~30 cents each from my UK component supplier) with 470R or 150R resistors, soldering the LED and resistor to a battery-holder clip, then potting round the resistor and LED base with epoxy.
The brightness difference between the two wasn't hugely noticable close up. In relative darkness, both seemed very brigh if looked at head-on, though the brighter one does seem to have a slightly larger apparent size if viewed from some distance.
Running off a pair of fresh AA alkalines, with one or other resistor, they pull 2.5 and 8mA respectively, which would give expected runtimes of ~1000hours or ~350hours, though in practice they will start to slowly dim from the word go, and and actually still be shining more dimly for somewhat longer than those figures suggest, as is the way with LEDs.
Off reasonably charged NiMH cells, the current+brightness are about 2/3 of the initial alkaline figure, with runtimes likely to be proportionately longer, but with maybe a little slower dimming than with alkalines.
I took a few out on an expedition last summer, and though they never got used for surveying, they proved excellent as path-markers for night-time navigation across a limestone plateau, being clearly visible from several hundred metres away, and even in mild mist, could still be seen from a reasonable distance.