Infos about 8x10 in. Carestream x-ray film

[barnacle]

Regarding the colour of LEDs - they come in two flavours. Some have a semiconductor which outputs a given visible wavelength (660nm seems to be the most common - a deep red) while some use a UV output and a phosphor to give a visible colour. The phosphors rarely have a single line spectrum and though visibly red can have significant output in blue and ultraviolet. That said, red is not *usually* a phosphor type... but the only way to be sure is to check the datasheet for the LED you choose.

For example - the first one I found at 660nm at Farnell - http://uk.farnell.com/kingbright/dlc...red/dp/1142477 - has a data sheet which states that the peak power is at 660nm and a spectrum peak width of 20nm - quite a decent single colour. The graph indicates that the peak is at less than 10% output by 640nm; the graph for Typon DV-G - http://www.typon-roentgen.de/fileadm.../DV-G_ORTH.pdf - says it's sensitivity is down to 1% by 630nm. I would be happy to use this as a safe light - though I would of course test it before using it in anger!

Neil

[koraks]

Embarrassingly, it seems that most high-powered white leds are in fact phosphor coated leds (UV or blue). Thanks for the, ah, enlightenment, Neil

[barnacle]

Yes, I should have said... red, green, orange, yellow, or blue are *most likely* direct, but white needs to trigger the red, green, and blue photoreceptors in the eye and the cheapest way to do this is with a phosphor.

Also - beware of RGB LEDs unless you are aware of how they are driven; you could be seeing a red through some controller which also allows some small amount of green or blue at the same time.

Neil

(Been investigating light paths of infrared LED/sensor pairs through polycarbonate prisms this week. First step: prove that the IR path is not too different from red, and then, fun with lasers!)