Custom LED warm white (2700k 95 CRI) dome light mod

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Joined
Jul 21, 2012
Threads
22
Messages
495
Location
Rhode Island USA
So as I get my 62 back up and going, I couldn't help but notice the dome light was pretty miserable. Just not a lot of light for a big space. Obviously there are drop in LED retrofit bulbs, but the majority of those suck, too. Most of them seem to be 5000-6000k color temperature - and I just absolutely despise that harsh bluish-white light, especially in a "vintage" space that's supposed to be "cozy". Not only do most of the LED retrofits have harsh color temperatures, they also tend to have poor CRI (meaning colors don't appear right), they run hot and don't last very long. The amount of LED retrofit bulbs I've seen dead or flickering is ridiculous.

I decided instead to modify my existing dome light with an LED module that I put together. I sourced some really nice LED "COB" (chip-on-board) modules from Digikey, and I screwed them down into a heatsink I found in my junk bin. This will ensure they will always run cool.
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These LED chip modules cost about $3 each, they're 2700k color temp and 95 CRI, meaning they just about match incandescent bulbs perfectly. Each one supports up to 15w max power, or about 3000+ total combined lumens running balls-out, but I won't be running them anywhere close to that. The heatsink I chose, which can you see installed below, is really only probably good for maybe 5 watts of heat continuous. Of course many drop-in LED replacements don't have any heatsinking at all, and run the LEDs at 150°C, which is why they have short miserable lives.

The screwdriver is a "Vessel Woody" for those curious. Great for oily hands, and fit Japanese screws perfectly.

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Below is a shot of the completed project. You will notice there's quite a few sets of resistors. I did this for two reasons: 1) it spreads the power dissipation across more resistors, so they'll run cooler, and 2) It gives me a dual-brightness functionality.

When set to "Door" the LEDs are run at about 1 watt combined power. At this power level they're still delivering about twice as much light as the incandescent bulb did to the interior, but it's not so bright that your eyes get blasted when you hop in/get out at night. When you turn the light to "On", it jumps up to just under 3 watts, over doubling the amount of light output. I figure this may be useful if you're trying to find something under the seats at night, or just any situation where more light than normal would be useful.

Feel free to hate on the soldering and wiring. I was trying to cram everything in there so that the lens cover still sat flush, nothing blocked the light, and that it still fit up in the roof channel. Also in my defense, whatever metal they used (appears to be stainless steel), does NOT like to be soldered. It was really, really difficult to make connections.

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Here's what the lighting looks like on "Door"
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Here's what it looks like when switched to "On" (bright)
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I did my best to adjust my crap phone camera, but it doesn't really do it justice. It's a really nice, high quality warm light, that perfectly matches the incandescent light, while being much, much brighter. I'm very pleased with how it came out.

My total investment in the project was about $10 for the LED modules and some resistors, and a few hours of time. I'll probably end up doing the rear dome light as well, since I liked how this came out. I think I may also see about tying the rear dome light into the front dome light circuit as well.
 
Cool project. I'd upgrade those 1/2w metal film resistors min. 1w metal oxide flameproof ones, though ... just to be safe. It's worth going overkill to not have a car fire.
 
They're 1-watt metal oxide flameproof!
Nice! They looked like the blue metal film from the photos, but I stand corrected.

Do you get any flicker? Slow start up? Does the voltage gauge nose dive when you turn it on? I haven’t worked with COBs before, but I’m considering using them for another project (retrofitting into a 1950s bicycle light). I’m wondering if a small capacitor bank would be helpful to alleviate any of the above issues.
 
Nice! They looked like the blue metal film from the photos, but I stand corrected.

Do you get any flicker? Slow start up? Does the voltage gauge nose dive when you turn it on? I haven’t worked with COBs before, but I’m considering using them for another project (retrofitting into a 1950s bicycle light). I’m wondering if a small capacitor bank would be helpful to alleviate any of the above issues.
No slow start or flicker. While these are "COB" lights, they're pretty dumb. They don't contain any active electronics, and you can treat them just the same as if they were a standalone single LED. I went with the "COB" format because it was much easier for me to mount. Otherwise I'd have to make custom circuit boards and solder fiddly small SMD LEDs to a board. Not something I was interested in.
 
No slow start or flicker. While these are "COB" lights, they're pretty dumb. They don't contain any active electronics, and you can treat them just the same as if they were a standalone single LED. I went with the "COB" format because it was much easier for me to mount. Otherwise I'd have to make custom circuit boards and solder fiddly small SMD LEDs to a board. Not something I was interested in.
Good feedback. I ordered some parts from Mouser for my bicycle headlight project yesterday, so we’ll see how it goes. The COBs are supposed to be pretty bright, so if this project goes well it might be nice to find some more solutions for the 60 interior lighting too.
 
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