|
|
Low Profile 12
Volt LED Bulb
 Necessity is the mother
of invention and at the
time of writing there doesn't seem to exist any 12 volt LED bulbs that
spread light equally in all directions both horizontally and
vertically,
provide a nice
ambience just like a traditional filament bulb and, very importantly,
don't stick out the
top of smaller lamp
shades
looking completely ridiculous.
When trying out light bulbs for use with solar
power, my aim is to find one that can reproduce the warm, cosy light
that
most
people including myself prefer, but I always seem to end up with a
shadowy,
uncomfortable 'spooky' effect which I believe is due to not enough
upward and downward light radiation. The ceiling is a
reflector that over time our brains have become used to perceiving
light
from and if removed, we miss it. This is also true,
perhaps to a lesser extent, of light
from the floor, maybe not so much from reflection if carpets are used,
but just because we are used to seeing it illuminated. I
wonder if there's such a thing as psychoillumics? The device
described here solves all these
issues by reconfiguring the position of four low power G4 LED capsule
bulbs to give a totally omnidirectional light dispersion
pattern in a low profile form factor
 The
assembly is constructed on a small piece of veroboard nine holes square
with the corners rounded off. This is so it can be mounted into the
plastic cap of a discarded Tetra Pak. It so happens that the pin
spacing of
a G4 bulb will fit a 2 way PCB screw terminal block and so four of
these were used to
mount the capsules to the board, connected together as shown
above. The section of wire link coloured Green is on the upper side of
the board, the rest being on the underside. The bulb is designed to
plug into a G4 (to whatever) socket adapter which enables it to be used
in any type of lamp fitting (these adapters are readily available
online). This is achieved by simply soldering two short lengths
of stiff copper wire obtained from some twin & earth, onto the
board. The pitch will automatically be correct and it's just a matter
of cutting them to length. Before doing so, prepare the plastic cap by
trimming off any internal seals that might get in the way, and make two
small holes for the wires to protrude through. Check that everything
fits together and then snip the two wires to length, removing small
pieces at a time until the bulb sits flush with the adapter. When all
looks good, the veroboard can be secured in place with Araldite. Most
G4
bulbs can be fitted either way round but if not, the polarity is marked
with a Red dot
 Most
LED bulbs that work on 12 volts are of the G4 variety. These are
usually low powered capsule types intended for things like small desk
lamps or under cabinet lighting etc. but not as main lighting. There
are many different styles available and I have tried quite a few, but
the best ones I've found so far are those with individual LED chips
arranged to fire light in all directions at 90 degrees to the vertical
(but not up and down
unfortunately).
Many LED bulb sellers give misleading power claims. The ones I
used here for example were listed as 4 watt, but when measured, only
consumed 150 milliamps at 12.5 volts. Simple maths makes that a
power of
1.875 watts, but I'm not too bothered though as they are really bright
and
if I can get that amount of brightness with less power then I'm happy.
The total current consumption of four capsules at 12.5 volts is 600
milliamps equating to 7.5 watts.
In fact, the current drawn is about 250 milliamps less than that
of an equivalent
brightness 12 volt 11 watt CFL bulb, which I think is pretty good! The
minimum amount of capsules required to create an acceptable light
pattern is three, but four gives just a bit more light boost to make
the extra capsule worthwhile. Anymore and it's a case of diminishing
return and current consumption should always be a
consideration if powering from a battery. Four is enough
to give an even, omnidirectional light along with brightness and economy.
As long as warm G4 capsules are used, the light produced will be
very similar to an old fashioned 60 watt
light bulb
 It also works great in a
garden shed
REMEMBER - THIS BULB IS DESIGNED FOR 12
VOLT OPERATION ONLY AND IS NOT TO BE USED ON A DOMESTIC MAINS SUPPLY
|