by Bryan Bergeron, Editor
Going Green with LEDs
Have you ever done the right thing for the wrong
reason? When I explored the option of replacing the
halogen bulb in my Electrix magnifying work lamp with
LEDs, I was simply tired of singeing my knuckles when
working on SMT components, and couldn’t find a
compact fluorescent to fit the bulb socket. I was also
looking for an excuse to work with the new high-intensity
LEDs on the market. Of course, the ‘right reason’ to make
the move would have been increased efficiency and an
associated reduction in greenhouse gases.
Figure 1 shows my work lamp before the LED
modification. A 100W halogen bulb sits recessed in an
aluminum reflector. Figure 2 shows the lamp after the
LED mod, with four LEDs flush mounted on a 2 mm thick
Figure 3 shows the upgrade components — a 24 VAC
output transformer, four high-power white LEDs, and a
constant current supply. The LEDs are 05027-PW14,
White High Current K2 Star LEDs, available from
www.LEDSupply.com. The $7.50 LEDs produce 100
lumens 1,000 mA at 3.85V, and a brilliant white 6,500K
color temperature. The constant current supply is a 1,000
mA BuckPuck, also available from www.LEDSupply.com.
Although both AC and DC supplies are available, I chose
an AC model (03021-a-1-1000 - $15) because I had an
extra transformer in my parts box. The BuckPuck accepts
7-24 VAC input and produces a constant 1,000 mA
output. An added feature of this model is a trimpot output
adjustment for varying the light intensity.
Wiring the LEDs is simply a matter of stringing the
LEDs in series and attaching the appropriate polarity of
the constant current supply to the string. I stuffed the
transformer and constant current supply in the head of the
lamp, in the space that was previously occupied by the
FIGURE 1. Work lamp
before LED mod.
8 May 2008
indentation for the bulb in the aluminum reflector. The
only downside to this arrangement is that the head is a bit
heavier than before, and I have to tighten the tension on
the supporting arm to keep it from drooping.
One of the challenges of maximizing the longevity of
LEDs is avoiding high temperatures. For this reason, I
elected to use a thermal epoxy (see Figure 4) to mount
the LEDs instead of using hardware. Sold by LED Supply
under the brand Arctic Silver Thermal Adhesive, the thermal epoxy ($13) makes short work of mounting the LEDs.
The epoxy has a five-minute working time, and you don’t
have to worry about drilling a dozen holes and possibly
over-tightening a bolt and shattering an LED mount. With
the thermal epoxy, the LEDs run warm to the touch, even
after hours of operation.
Using my Sekonic light meter, I determined that the
light output is only about a quarter of original output with
the halogen bulb. However, the lamp provides more than
adequate illumination. In addition, it’s cool, the light is
white, and I can work with the LEDs a millimeter from my
hand in total comfort.
From a purely economic standpoint, the conversion
was costly: $32 for the LEDs, $15 for the constant current
supply, $10 for the transformer, and a scrap piece of
aluminum. However, the LEDs will outlast several of the
$25 halogen bulbs required by the original lamp design
and consume significantly less energy. In addition, I now
have a pure white light source that’s perfect for close-up
video and still camera work.
Several years ago, I made the move from incandescent
bulbs to daylight compact fluorescents, primarily for
the white light, and I haven’t looked back. For many
consumers interested in going green, LEDs, halogens
bulbs, and compact fluorescent bulbs are becoming more
popular as the price for these alternative light sources
drops. Eventually, the move away from incandescents
will be mandatory.
According to a
passed in December
bulbs will begin to
be phased out in
2012, with a
finalized in 2014.
Under the measure,
all light bulbs must
use 25% to 30% less
energy than today’s
FIGURE 2. Work lamp
after LED mod.