Fun With LEDs

I've been replacing mains power gadgets around my house with battery-operated versions for a while now.  An average bedside alarm clock designed to run from the mains will consume up to 6 watts, or 50 kWh of power a year.  A travel clock designed to run from a AAA battery will run for the same period on the equivalent of less than 1 kWh a year.

The latest to be replaced is the bedside lamp.  I bought a mechanic's LED torch on a stand that ran off 3 D cells.  Worked reasonably well, but not as bright as I had hoped.  Unless it is pointing right at the book you are reading, it doesn't illuminate much.  So I decided to build my own LED-based lamp, using one of these:

That's a Cree Super Bright White LED.  100 lumens of white light, driven by 3 volts @ 350 mA, with a beam angle of 90 degrees. For comparison, a traditional 60 watt light bulb puts out 800 lumens. Here's the finished product:

The circuit is built inside a box with a clear lid, pointing straight up.  The original plan was to put a diffuser on top of the box to spray light in all directions.  I tried various diffusers, but the best was a bottle of clear marbles:

Turned out I didn't need the diffuser after all.  100 lumens across the 90 degree beam angle spread means that sitting on the bedside table, pointing straight up at the ceiling, it lights up the whole bedroom.  More than enough to read by.  And then some.

Power consumption is 1 watt, and should get about 30 hours on the two D cell batteries.

Parts list (with Jaycar part numbers):

    ZD-0442 - Cree XR-E Super Bright White LED (or Warm White ZD-0444)
    HH-8580 - Heatsink for LED
    AA-0590 - LED driver module, 3V to 350 mA
    PH-9218 - D cell battery holder x 2
    ST-0554 - Toggle switch
    HP-9556 - Veroboard PCB
    HB-6248 - Polycarbonate box with clear lid
    HP-0815 - Rubber feet
    Optional: 25 degree collimator lens (HP-1297)
    Mounting posts/spacers/nuts for the PCB
    Double-sided mounting tape for the battery holders

Total cost of parts is about AUD$90, batteries not included.  And here is the circuit diagram:

If you use the collimator lens to focus the light upwards, then you'll also need a diffuser like the aforementioned bottle of marbles.  Or stand it on its side to use it as a directional torch!