LED lamp fixes

A lightning strike from a recent thunderstorm killed my USB-powered LED lamp I designed in 2005. The PC still works. I haven’t figured out how to get this building grounded, which it probably isn’t, given the number of lightning-damage incidents I’ve had…

This was supposed to be a post about how I got replacement LEDs wired up and the lamp system was working again. Almost, not quite.

The old LEDs used were standard 5mm white LEDs, underdriven with a big power resistor. There were 2 arrays of 9 LEDs each, wired in parallel. The new, 8mm LEDs are 0.5W each, but have an amazing 140° viewing angle, much more than the typical focused-beam kind (around 15°).

LED numbers are confusing. Lux, lumens, candellas typically indicates brightness for LEDs, but so does wattage (nearing the realm of light bulbs). After some searching, I think 0.5W means they output 110,000mcd.

The new LEDs, mounted, before having their contacts coated with epoxy:

Test-lit with 3V:

I planned on powering the LEDs by hijacking a LED-based night light, which is quite the value at USD $1.50, for a light that should last several years:

The clear circle at the front lets light fluctuate the resistance of the photosensor, which varies the current reaching the LED.

I basically extended the photosensor and LED leads, so that they can be placed outside of the unit.

These two components are the ones with the red and white candycane-like insulation on their leads.

I placed the photoresistor at the front corner of my desk, near a room window, so natural light can actuate it:

Here’s what it should look like (picture taken the night before):

Actually the light pattern is 1/4 as strong, or less. Blame the photographer ^^;

Anyhow, I had left the LEDs circuit open, because I installed a toggle switch of course; upon closing it (after a few hours), the LEDs burnt out. Somehow too much current had pooled. My experience with electronics is little. I’ll likely be replacing them yet again. I could attempt the night light mod again, this time placing the power switch for the mains, instead (but would have to wait for my soldering iron to arrive first). Instead, I may revert to a simpler manual on/off toggle. I would like for the brightness of each to be the same, and should achieve that by wiring them in series rather than in parallel. Not sure if I will either draw power from a AC to DC “wallwart” adaptor, or a 12V rail from my PC’s power supply…

Update

I redesigned the ceiling terminal hookups. The old one was over-designed, and unreliably friction-fit.

The vertical clearance is much less using this screw-on cap, but it matches the rest of the design better.

This mix of original and revision 1 design suffers some still (the tubing tends to go crooked, as you can see below) until I can figure out an alternative mechanism to keep the tube from falling.

It may be hard to tell, but the brightnesses are equal at least, by wiring the LEDs in series rather than in parallel.

The pattern casted on the wall is a bit misleading in these pictures. It is actually very faint and less saturated and pronounced.

These are running off of AA batteries (4×1.5V) until I figure out a suitable power source.

04:32 AM | 7 Comments | Tags: make