[VAC] Re: Compact Flourescent Bulbs

[Dr. Gerald N. Johnson, electrical engineer]

I've been doing some studying. My Caravel has three ceiling fixtures,
each with four 1141 lamps. The rotary switch allows selecting 1, 2 or 4
lamps at a time, 17, 35, or 70 watts. Each 1141 is rated at 21 candela.

I looked at white LEDs. The largest output I found without digging too
hard was at Hosfelt Electronics, (www.hosfelt.com), 7000 millicandela,
or 7 candela. 1/3 the light output of an 1141. The power to the white
LED is 4 volts at 20 milliamps, .08 watts. Its not a drop in part yet,
the LED costs $5.99 each and requires current regulation to protect it
from large changes in current with small changes in voltage. 3 in series
should be close to working directly from 12 volts with a bit of current
control. I'm thinking about circuits. The other problem which may be an
advantage in some applications like reading lamps is that the beam is
narrow, maybe 28° included angle. For general trailer lighting this
could be a limitation. There are multiple solutions, the conceptually
simplest one is a cluster of LEDs each at a different angle to fill in
the hemisphere of lighting needed for general ceiling lights. I'm
thinking some sort of spreading lens or reflector or a combination of
the two might be practical. It might even be practical to defocus the
dome on the front of the LED. I wasted many red LEDs a few years ago
trying to make them focus tighter... Dispersion was far easier to
accomplish.

I've ordered three of the LEDs from Hosfelt. They seem to promise the
same light level (if it can be spread enough) for 1/100 the power.
That's far better than the fluorescent fixtures.

Its harder to find fluorescent fixtures using compact fluorescent lamps
to run off 12 volts. Most use either the 5/8" diameter by 4 to 8"
tubular lamps or circuline lamps. Neither are great for efficiency or
commonly available in improved colors, though are very commonly
available as 12 volt operated fixtures and as replacement lamps.
Generally the small tubular lamps and compact fluorescent lamps are
rated at different powers so their ballasts can't be swapped
successfully.

The first batch of white LEDs should be here about Thursday, then I can
begin to experiment.

1141 lamps are on the hooks at Walmart in automotive lights. $1.97 for a
blister pack of two. There's also 12 volt 18 watt lamps in a similar
package in the RV section, $.97 for a blister pack of two.

There is a single LED flashlight at Walmart (flashlights are in sporting
goods) for $11.96. It runs on 2 AA alkaline cells.

Gerald J.



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