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A low cost adjustable red darkroom lamp

  1. stormpetrel
    Hi guys

    This is a very simple low cost DIY project I would like to share with you.

    The lamp is built around 4x high power 660nm LEDs and an adjustable linear voltage regulator (LM317T).
    The power of this LED lamp is around ~9W (~ 80W light bub)

    Here is the schematic

    Darkroom proportional LED lamp by stormpetrel_geek_mode, on Flickr
    U1: LM317T (1.5A adjustable voltage regulator)
    U2: AC/DC converter, ouptut 15VDC-17VDC, 1A (1.2A max). Any low cost power supply would do the job
    R1: Resistor 30 Ohm 1/4W
    R2: Potentiometer 220 Ohm (cermet highly recommended as they last far longer than carbon potentiometer)
    L1, L2, L3, L4: LED LZ1-30R200 or LZ1-10R200 (660nm,If=1A,Vf=2.5V) (available at mouser)

    U1 and L1-L4 must be mounted on heat sink with thermal adhesive pad or thermal past glue

    The "tab" of U1 is at the same voltage as the output pin. As it might be in direct contact with the heatsink (some thermal past are electrically conductive), it would be better to avoid connecting the heat-sink to the ground (leave it floating).
    All the LEDs and U1 might be mounted on a single heatsink (150mm x 100mm x 20mmwould do the job).

    A picture of my DIY lamp:

    DIY darkroom lamp by stormpetrel_geek_mode, on Flickr

    DIY darkroom lamp by stormpetrel_geek_mode, on Flickr
    Note the button on the right side to adjust the light intensity.
    I have used a piece of red glass as a screen but this is only for esthetic purpose. You might use a piece of translucent plastic instead.

    DIY darkroom lamp by stormpetrel_geek_mode, on Flickr

    4x Leds is enough for my 6sqm darkroom. I use the lamp between 1/4 and 1/3 of the maximum intensity most of the time but you could use more LEDs by changing R2 value and by using a higher voltage power supply (eg 8x leds with a +24VDC/1.2A power supply)
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