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 three low power G4 LED capsule bulbs to give a totally omnidirectional light dispersion pattern in a low profile form factor
The assembly is made from a discarded CFL bulb, in this case a BC (B22) type which is common here in the UK, but other types can also be used if prefered. With a junior hacksaw, carefully cut the base section away from the tubes taking great care not to break the glass. Remember that CFL tubes contain mercury and should be disposed of according to your local recycling rules. After removing the old circuit board you should end up with something like the photo below, ready for the new LED assembly to be mounted. This is constructed from veroboard the layout of which is shown above. By pure luck, the CFL bulb I used had four slots near the top where the corners of the LED board could conveniently clip into which was a bonus, but Araldite was also applied in each corner to secure everything in place. It so happens that the pin spacing of a G4 bulb will fit a 2 way PCB screw terminal block and so three of these were used to mount the capsules to the board. The two that are at an angle to the copper strips need a bit of encouragement when fitting as the distance between the holes will be greater, but they should go in OK. 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 three capsules at 12.5 volts is 450 milliamps equating to 5.625 watts. In fact, the current drawn is about half that of an equivalent brightness 12 volt 11 watt CFL bulb, which I think is pretty good! More than three G4 capsules could be used but current consumption should always be a consideration if powering from a battery. I have found three to be the 'sweet spot' that will still 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
To get the maximum amount of light for a given bulb brightness, a neutral coloured shade (White, Cream, Natural etc.) is recommended
It also works great in a garden shed!
WARNING: THIS IS A 12 VOLT BULB. DO NOT CONNECT IT TO THE DOMESTIC MAINS SUPPLY!