I'm with Fran on this one. Please do the Kodak test, it will only take 10 minutes and it will save out $$$ in paper, but above all, in frustration spent in chasing good contrast. The test is here: http://www.kodak.com/global/en/consu...Safelite.shtml
Originally Posted by fran
Coin test does not tell you the full picture. You may have a safelight that passes it, but which can still fully depress the highlights in your prints, causing you to overcompensate with high contrast settings.
Second to this, in importance, is making sure your enlarger does not leak too much light.
Well done for building such a neat device.
Ps. My LED safelight works but it required an addition of a red filter. LEDs differ, and even the purest deep red, as checked by the CD/prism test mentioned by Ken, will affect paper if too bright.