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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 (Hi to all the folk at Men's Shed Electronics!)


REMEMBER - THIS BULB IS DESIGNED FOR 12 VOLT OPERATION ONLY AND IS NOT TO BE USED ON A DOMESTIC MAINS SUPPLY