DIY LED lighting fixtures

[opiesche]

Hi all,

Wanted to show off some pictures of a more or less recent project

I built some partition walls around an open family room a few months ago, to convert it to an office. In the process of building the walls, I mounted LED transformers (one 48W and one 20W) to two of the studs, ran low voltage wires through the walls and ceiling (the light switches are switching 12V), and custom built some LED lighting.

I used this sort of LED module:

Warm White LED Module 12V Waterproof 5050 SMD 4-LED/PCS Light 20pcs $20.95 Free Shipping @GoodLuckBuy.com

They contain four 5050 type SMD LEDs each, run about 0.7W and output on the order of 60 lumens a piece. A string of 20 of them is around 20 bucks at the link above - I haven't found any LED lights for a lower price per lumen.

I cut a strip of 1/4" plywood about 2 inches wide and about 1 1/2' long, then glued 10 modules each on them (Loctite PowerGrab is a great adhesive for this, by the way!).
Then I cut a strip of acrylic about 1 1/2" bigger on both dimensions than the plywood (I use a jigsaw, since I never can get a straight edge with scoring and breaking the acrylic. Sprayed both sides with Krylon frosted glass spray, drilled 3 holes through both acrylic and plywood, and bolted a 1" binding post through each hole with a matching bolt from the back of the plywood.
The plywood is then simply screwed to the ceiling and the acrylic mounted on the binding posts with the same screws. The results are two fixtures in my office that look like this:



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Uploaded with ImageShack.us
Then I just finished another one for the other side of one of the partition walls, which now forms a rather dark hallway with an existing wall. For this one, I followed the same procedure but different dimensions and used 12 modules instead of 10, and also glued a piece of aluminum L-profile to each long side of the fixture for a more finished look. Fast exposure that shows the LEDs:




And the end of the hall along with it:



So far, I'm pretty pleased with the results. Next I'll build three more of these that will hang from decorative chains in my kitchen to replace the three fluorescent fixtures at 75W a piece I have in there now

[Daox]

Those look really nice! Sounds like you came up with a great way for a good looking fixture that is also quite inexpensive.

Where did you get your transformers?

I just ordered some parts yesterday for my first LED project. I have a staircase that I want to light up at night. I'd like to mount my LEDs under the handrail and have them illuminate the stairs. I'm also going to get a little fancy and use some PIR (passive infrared) motion sensors on each end so there won't be a need for any switches. I still have no idea what LEDs I'm going to use though.

[opiesche]

I've used this one for the office, and a similar (smaller) one for the hallway.

Led Wholesalers Waterproof Electronic LED Driver Transformer 48 Watt 120 Volt to 12v 4 Amp

If you just do a google shopping search for 48W LED transformer (or whatever the wattage you anticipate needing is , these pop up. They're fully electronic, so they have a high efficiency and low heat output, have built-in overcurrent and short circuit protection, and work well

[Daox]

If you could do a write up on how to build one of these with a few more pics, I'd really like to put it on the blog.

[opiesche]

Gladly. Do you want me to just post it to this thread?

[opiesche]

OK, so here's the step-by-step description of my process - YMMV, of course, and there's plenty of room to change and improve

Building these fixtures is relatively easy, and the materials come out to about 20 bucks a piece - less if, as I did, you still have a bit of spare plywood and acrylic sitting in your workshop
This is also assuming that you've got 12V wiring and power supply for the LEDs ready. I placed transformers in the walls and rewired the light switches with low voltage wiring (a regular light switch works just as well with 12V as it does with 110).

Materials:

1/4" plywood (about 7 bucks for a 2'x4' sheet)
A strip of acrylic (about $25 for a 2'x4' sheet)
1/2" - 3/4" binding posts and matching bolts (roughly $5 for 10 or so)
Adhesive (~$5 depending on type)
Aluminum L-profile ($6 for a 4-foot piece)
LED modules (Warm White LED Module 12V Waterproof 5050 SMD 4-LED/PCS Light 20pcs $20.95 Free Shipping @GoodLuckBuy.com - $20 for 20 of them)

Before starting to build, it can be useful to make a few calculations for the fixture. How much light do you need? Based on that, what kind of transformer do you need?

Number of modules = number of 15W CFL bulbs * 7
Wattage = number of modules * 0.7

For example, a 15W CFL bulb output about 400-450 lumens. In warm white color temperature, the modules linked to output in the ballpark of 70 lumens a piece. That means for the same amount of light a single 15W CFL produces, you'll need 6 or 7 of the modules.
Each of the modules consumes on the order of 0.7W according to the LED's specs (I haven't measured it), which means for one fixture with 12 modules, the transformer has to handle at least 8.4W, or 700mA at 12V. I've got a 30W transformer in the wall, so I opted for three fixtures with 12 modules each for a total of 25W - it's a good idea to give the transformer a little headroom (on the order of 5-10%), because the power consumption is going to vary a little from module to module.

This is the transformer I used:
Ledwholesalers 30 Watt LED Power Suppply Driver Transformer 120 to 12 Volt DC Output, 3207 - Amazon.com

Now for the fixture:

First, I cut a piece of plywood (I used 1/4") to the size needed for the fixture. The LED modules are about 1.5" square, so anything bigger than that will work - the dimensions really depend on the shape for the fixture, and the arrangement of the LED modules.



This doesn't have to be pretty, as it'll be mostly hidden from view. Painting it the color of the wall before mounting the LEDs will make it nearly invisible. I imagine you could use any other substrate for this as well (like a second strip of acrylic), but the plywood is easy to work with and I had some spare strips.

Drill at least two holes big enough to fit the bolts for the binding posts. The amount and location depends on the desired look and size - the bigger the fixture, the more are needed to keep the cover solidly attached.

Next, I cut a strip of acrylic to size. This should be about 1" bigger in both dimensions than the plywood. To cut, I use a jigsaw because it gives me straighter cuts than scoring and breaking the acrylic - clamp down the acrylic with a board to use as a guide for the saw. Use a fine toothed saw blade and go slow to prevent the acrylic from chipping.



After cutting, clean both sides and spray with frosted glass spray. Two coats is usually enough to get a nice frosted surface. It's a good idea to do this outdoors - not only are the fumes from this stuff pretty gnarly, it also prevents some of the dust undoubtedly floating around in the workshop from settling on the wet spray and messing up the finish



While the acrylic is drying, we can mount the LED modules. They come in a string and can be a pain to mount because you end up pulling the previous one out of position with every one you glue. I can highly recommend Loctite PowerGrab for a job like this - it's got really strong tack while still wet, so the modules are less likely to shift around until the glue is dry.



I squeeze a small amount of the adhesive on the back perimeter of the module and then just press it in place with my fingers. A few pounds of pressure are enough to make it stick well, and they won't move easily after that. Arrange all the modules on the plywood, making sure to not cover up the holes drilled for the binding posts and bolts.



After all the modules are in place, bolt a binding post through each of the holes. The cover will later attach to these.









Now I put the frosted acrylic on top of the binding posts in exactly the final position to mark the holes for drilling. Drill holes through the acrylic where the posts will go - start with a small drill bit, go slow, and use very, very little pressure, otherwise the acrylic will tend to crack. Then expand the holes with a bit matching the size of the bolts. Clamping down the acrylic is a good idea, as it tends to be pulled up the drill bit and slam into the drill once the bit goes through otherwise.


With that, the back end is complete. At this point, I already screwed it to the wall with a few drywall screws and wired it up.

Next, I took a piece of aluminum L-profile



and cut two pieces about an inch longer than the long sides of the fixture. File off the ends to
Put a small amount of adhesive into the inside corner of each L - just enough for a thin layer, so it doesn't ooze out the sides and become visible from the front - then press the frosted acrylic into it. At this point, I weighed it down and let the glue dry for a few hours.






Finally, attach the cover to the fixture by bolting it into the binding posts. Done



In addition to the wall fixture, I've also got two ceiling fixtures built the same way (but without the aluminum profile along the sides) in my office:

[Daox]

Awesome write up, thanks!

I do have a few questions though:
The LED website says each module only uses .3W, but you say .7W. Why did you quote a higher number?
Also, the site you linked doesn't say that each module puts out 70 lumens. Where did you get this info?

[opiesche]

As for the wattage, ir's because I think the seller's web site is wrong. The 5050 type LEDs are spec'ed at 0.19 watts (Warm White 5050 SMD LED | Component LEDs | Super Bright LEDs), which makes a little over 0.7W per module.
It's important to keep in mind though, that 5050 is just the size of the chip - different manufacturers mame 5050 LEDs with different characteristics. In this case, I figured it is better to err on tbe high side. My multimeter is broken, but I'll measure current through o e module when I get a new one.

For the luminous intensity I used the 6000mcd and 120 degree beam angle from the spec, converted using an online converter, and subtracted a few percent to err on the low side of the intensity

[opiesche]

OK, so I just connected a 1 Ohm resistor in series with one of the modules, then measured the voltage across the resistor as 0.08V.
Ohm's law says that

I = U/R

So that makes for 80mA of current through the module. The voltage across was only about 10V, which makes for about 0.8W for that module. This was for a cool white with ~10000K color temperature because that's what I had laying around
The warm white have on the order of 3000K color temperature, and I anticipate them drawing a little, but not significantly less current. Looks like the specs aren't too far off - tolerances notwithstanding, it seems 0.7W is pretty close for the warm white LEDs.

[opiesche]

I just measured the resistor as well, and it actually shows at 1.2 Ohm, which brings us to

I = 0.08/1.2

So around 66mA for one module, or 0.66W at 10V.