Light Source Comparison
The Philips bulbs failed in my Tri Color enlarging head. With replacements cost at $25 to $30 a piece, I decided to look at different light sources.
I realigned the enlarger assembly and installed the PH212 150 Watt bulb and condenser system. I inserted a Stouffer 21 step wedge into the negative carrier, focused and locked every thing in place.
I printed a set of 5 X 7‘s using Kodak Variable Contrast for #1, #2 and # 4 filters. I added a set using Wratten Filters numbers 80C (light Blue), 49 (Dark Blue), and 40 (light green)
I switched the light source to a cobbled head assembly using a single Cree XR7090 XR series 3 watt LED. I print a set of 5X7’s for Royal Blue (455-465nm wave length), Green (520-535nm wave length), and White. The condenser set was retained.
All was printed on Kodak Polycontrast Rapid Paper developed in Ilford MultiGrade.
The step wedge prints were visually compared to a standard Kodak gray scale for a density of 0.1 and 1.9. The corresponding step number was recorded for each density.
Kodak filter should produce 5 1/3 stops for a # 1 filter and 3 stops for #4. These results are with my test error.
The Green LED produced 5.5 stop range which is comparable to a #1 filter. The Royal Blue LED compared to a #2 Filter while the White LED pushed to #2.5.
Standard PH212 150W Condenser System
--------------------------Zone VIII-Zone II-No of Steps-Stops
80C Lt Blue__30sec f11_______15____8_______8______4.0
40 Lt Green__30sec f11_______4_____2______13______6.5
49 Dk Blue___30sec f11_______9_____4_______6______3.0
LED's Light Source
Hope this chart makes some sense.
I guess I will test with Halogen next. :rolleyes:
I do not completely understand your test, but my question is other.
As far as you know, are the white leds a possible substitute for say, the lamp of my V35 focomat (halogen 75 watts) ?
How many watts white leds are necessary to equal a 150 watts photo bulb ?
Last of my dumb questions, do lumileds get hot ?
Very hot ?
Do they need a special heat sink ?