# Convert a Vintage Light to Component LED

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I bought a cool-looking vintage photography spotlight at a garage sale that I thought would make a great looking desktop lamp or reading light. The bulb was burned out and the base was a rare twist lock that is no longer available. For the conversion I bought a chip-on-board (COB) LED. LEDs require constant current and precise thermal management. I'll use a driver with a constant current of 300ma and a forward voltage of 21. A quick calculation using Ohms law has my LED working at 6.3 watts. A finned heat sink rated up to 10 watts will handle the heat.

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## Step 1: Pick You LED First

I chose a high power COB LED with a color temperature of 3,200 Kelvin, or about the warmth of an incandescent bulb. COB chips pack small LED together on a single chip. The maximum drive current for this LED is 500ma, but I chose a driver at 300ma to stay within the wattage rating of the heat sink.

## Step 2: Heat Sink for Thermal Management

High-powered LEDs require you to stay below a certain temperature or they will fail. My LED forward voltage is 21 volts with a driver delivering 300ma. Volts times Amps = Watts (21v x .3a) gives me 6.3 Watts. I chose a heatsink rated at 10 Watts to be safe. I'll use thermal paste before attaching the LED to ensure good heat transfer.

## Step 3: Mount the Heat Sink and LED

After tearing the guts out of the spotlight, I fashioned a 90-degree bracket that put my LED at the center of the reflector. I coated the heatsink with thermal paste and screwed down the LED. This LED is mounted to a star that allows two soldered connection on the front of the chip. It has two positive and negative connection so you can daisy chain chips. Just remember that if you chain the chips, your driver's voltage must be greater than the combined forward voltage of the chips and be of sufficient wattage.

## Step 4: LED Driver and Mounted Chip

I pulled the case off the driver to enable it to fit inside the spotlight. I'll cover it in plastic to keep it from shorting out on metal case. It is a 120 volt AC to 21 volt DC constant current driver I bought on Ebay.

I added a reflector to keep light spill to a minimum. You can add optics to focus the light, but this spotlight has a glass Fresnel lens to handle that task.

## Step 5: Testing Before Assembly

A quick test shows the LED is working properly. I realize the old reflector is not doing anything, but it's not in the way. High-powered single LEDs throw a fairly narrow beam, while COB chips are quite wide.

At 6.3 Watts, the bulb is equivalent to a 65 Watt incandescent, or about 850 lumens at 3,200 kelvin. I intend the light to be on a desktop, so the light is not overpowering or too blue.

## Step 6: The Assembled Case

The LED is dead-center on the fresnel lens. The spotlight has a twist knob to adjust the distance to the fresnel and the beam angle. Yes, I could have converted the light using a small 30 Watt halogen, but I decided to go small and efficient. The case is much too small for a standard bulb. You may see LEDs rated with a CRI. The rating is a measure of the quality of light. Colors look better with higher CRI ratings. This LED's CRI comes in a 85. That's a B+ for light quality. Anything above 90 will render colors that are the most pleasing to the eye. The rated life of this chip is 40,000 hours, or about 40 times longer than a standard incandescent.

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## 24 Discussions

Would these be dimable ?

I used these lights back in the early 70's when I worked in Photo during high-school. I would love to make a pair of these for vanity mirror location for my wife...the look is great

7 replies

Good information - I was browsing eBay with this info and see several LEDs of your description being sold. Questions - 1. The price seems to be around \$1.50 so they are not too expensive. How long have these lasted in your projects? 2. Did you derate the current?

In this project I used an LED rated to 500ma and installed a driver at 300ma, derating it by quite a bit. After just a few hundred hours the LED started to dim. I replaced the cheap COB with a Cree CXA 1310 array and it has functioned perfectly.

Connect a variable DC supply to it to dim it instead of the AC hookup and AC converter module.

That would be fine for a lab workshop enviroment, but daily household use would be a different story

Because this was my first conversion, I kept it simple. Just buy a dimmable driver and matching dimmer available at places such as LEDsupply.com.

LED technology is evolving by the day... if you ever have anything serious to do with them buy only the ready made bulbs from the most recognizable brands. I have LEDs mostly "Made in China - sold on eBay" kind of stuff (fitted by the previous owner) at my place that are about 1 year old. Purchased branded LEDs at Costco @\$1.50 per bulb. There is no comparison in brightness, energy savings and overall life!! In my previous house I tried experimenting with DIY LED projects but thanks to the lack of quality control (on eBay and other popular websites) none lasted more than a few weeks. My projects have spanned COB and non-COB LEDs... COB LEDs are the ones used in this project... these are especially bad and none lasted for more than 3 days. I tried under rating them by reducing the quiescent current to half that is rated but that wasn't encouraging either. Having warned you of the futility of this exercise, I hope that if you still do this project, you are luckier than I was!!

I hear you and I have experienced that lack of quality control. I've done a couple of other modifications using both the Cree Xlamp and Luxeon high power LEDs on 20mm stars. I'll never go back to the cheap COBs.

Great job and 'able. I have been doing some experimentation with some high-power LEDs also.

I think they still make these:

http://www.bhphotovideo.com/c/product/42236-REG/Photogenic_908882_CL150FS_200W_Minispot.html

2 replies

Wow. I bought mine for\$10 at a photo garage sale.

Looks like they're going for 150 or so on E-bay. I would've made a lamp out of it too.

I should have just sold it on Ebay! I had no idea.

I can't tell from the photos whether the lamp housing allows airflow past the fins of your heatsink, but hopefully you realize that approximate "10 Watt" rating assumes unimpeded airflow in an ambient environment close to room temperature (which it would not be if the housing traps the heat generated). If the original bulb cavity is more or less closed off completely, the equation changes significantly. But an array of vent holes or slots could greatly improve convective airflow if that is the case.

Still, it's a really cool-looking retrofit, and your efforts to use proper heatsinking are certainly much better-considered than some of the rather shortsighted LED lamp Instructables I've seen here lately.

2 replies

As Filmist correctly commented, the body has large slits at every rib for extensive ventilation. And thank you Filmist for the bulb source.

I've owned this original lamp before, and the housing was designed to cool a 250-W tungsten halogen lamp. There's plenty of air flow through the lamp.

:-J

An urgent lack of cooler is detected. 50 mm would be perfect.