Light Source Comparison

Discussion in 'Darkroom Equipment' started by B Kumpf, Mar 6, 2007.

  1. B Kumpf

    B Kumpf Member

    Jan 18, 2007
    4x5 Format
    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
    ------------------------------------Step Number
    --------------------------Zone VIII-Zone II-No of Steps-Stops
    1_________30sec f11_______16_____7_____10______5.0
    None______30sec f11_______16_____8______9______4.5
    #2________30sec f11_______15_____8______8______4.0
    #4________30sec f11_______11_____6______6______3.0

    Wratten Filter
    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
    Blue________30sec f11_______13____6_______8______4.0
    Blue________60sec f11_______11____4_______8______4.0
    Green_______60sec f11_______11____1______11______5.5
    White_______30sec f11________7____1_______7______3.5
    White_______60sec f11________9____3_______7______3.5

    Hope this chart makes some sense.

    I guess I will test with Halogen next. :rolleyes:

  2. Biglou

    Biglou Member

    Mar 16, 2007
    35mm RF
    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 ?

    Thank you