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Longwave LED Display Light

Display.jpgHigh-Power Longwave (LW) Display Light

I have long ignored longwave light designs.  Greenland minerals are so bright under LW that an ordinary blue lightbulb will make them fluoresce, so I've always been content to use regular old "blakcklight" bulbs.  Recently I decided to build a high-power flashlight using state-of-the-art 365nm LEDs (real 365nm LEDs, not the junk you find on Ebay).  The results were shocking!  So I decided to tackle a light that can be used in our stationary displays.  Everything on the market is based on fluorescent bulbs and typically "Wood's Glass" filters; they put out way too much visible blue, and are very underpowered. The better ones are really expensive.  With today's LEDs it's possible to build a kick-butt light for not a whole lot of money.

Each LED emits about the same amount of UVA as a Phillips 9-watt BLB, but unlike fluorescent bulbs the light is unidiretional - it all comes out the front in an intense pinpoint beam.  No energy is lost out the back, having to rely on a reflector to redirect it, and blocked by the bulb itself.

You may build this lamp using one to five LEDs for a total UV output equivalent to 45-watts of fluorescent lights (remember, a 9-watt fluorescent doesn't put out 9 watts of UV; the UVA output is around 1.4 watts).  I chose 3 LEDs aa a good balance of power vs. cost (the LEDs are the most expensive parts).

As in all my projects, you'll need a little bit of technical/mechanical skill and the ability to follow directions to the letter.  I tried to make this project as simple as possible; I used components that are easy to hook up and tried to minimize the amount of soldering needed.  There are somewhat cheaper ways to do some of it, but you have to be pretty advanced to tackle those methods.

fini-filter.jpgTotal parts cost should run under $120 and should take even the most inexperienced DIYer just a couple of hours to complete.  It operates off low-voltage AC so there's no dangerous voltages involved.  The most complicated task will be soldering the LEDs.  The parts list is to the left.  There are cheaper parts in many cases, and certainly other ways to do it.  For example, you could use DC to power the lamp instead of AC and make it portable.  BUT - please don't barrage me with questions about using this part from Joe's Surplus Store, or a cheap knock-off from China.  If you want to experiment on your own, feel free, but don't ask me to bail you out.

Parts

Parts: Above are all the parts laid out.  This pic has three LED lenses that I decided not to use (they blocked too much UV) so ignore them.  The main components are the big heatsink which double as the case, the the three high-power LEDs from LEDengin.  The rest are an LED driver, a terminal strip to simplify wiring, an on/off switch, and a 5mm jack for power.  The power supply is a 24VAC transformer that just plugs into the wall.

The heatsink is a novel design by Makersled used mainly for building aquarium lighting.   Complete details can be found here: http://www.makersled.com/products/makersheatsink/.  I used the 6" model but of course if you want to build a megawatt light just scale up.  The Makersled web site is excellent and offers complete instructions on mounting the LEDs, assembling the unit, etc - so I will just touch on that here.

The core components are the LEDs, high-power 365nm LEDs from LEDengin - complete spec.  You'll find cheaper versions from China all claiming to be "high-power" and 365nm.  They aren't - these are the best offered today for the price. Keep in mind these are the most expensive part of this build, and they are delicate electronic components.  When you receive yours they will be wrapped in static protective packaging - for a reason.  Do not unwrap them until you are ready to use them, and make sure you are not "charged up", haven't just scuffled across a shag carpet, or played with a Tesla Coil.  You will blow them up with just static electricity.  Sit down, ground yourself (touch the dog's nose, zap your wife, touch a doorknob, or preferably touch a grounded outlet, toaster,  (FWIW - I've handled static sensitive components all my life and never damaged one.  Just be careful).

The rest of the components consist of a switch (way overkill, but it has screw terminals - make it easy to hook up.  In my actual project I used a much smaller, cheaper one and just soldered wires), a terminal strip so you don't have to make wire splices, solder, and heatshrink, and a 5mm power jack (you'll have to solder that).  The silicone paste is for heat - more on that later.

Wiring

Schematic - Some might call this a schematic of sorts.  It's a picture wiring diagram showing how everything is hooked up.  Note the symbols "+" (positive) and "-" (negative).  These are important - real important.  In the world of electronics they are called polarity - just like in your car.  Red is typically positive and black is typically negative.  I'll discuss this in detail below, but use this drawing to make sure everything is hooked up correctly.

I tried to use the same color wires as you will see on your actual parts.  The green lines are AC and do not have a polarity - doesn't matter how you hook them up - just matters where you hook 'em up.  All the wires go into the white terminal block which simply connects the four different sets of wires together (for example, the blue wire out of the LED driver (labeled "Luxdrive") is connected, thru the strip, to the black wire going to the neagtive connection on the one of the LEDs. (NOTE: I show the AC wires out of the Luxdrive as green.  They are really brown).

LED wiring

LED Wiring - the first thing we have to do is wire up the LEDs.  This must be done before mounting them in the heatsink.  If you try to solder after they are mounted in the heatsink (the heavy aluminum thingie with fins) it will take approximately 53 years to get them hot enough to solder. 

Do this carefully.  There are lots of tutorials on the internet about soldering to the little "stars" that the LED is mounted on - google it.  Note that the stars have little gold pads that are numbered.  Each of these pads have a polarity and must be connected as shown.  If you hook any one up backwards, it will be destroyed - no ifs/buts.

As the pic shows, a red wire is connected to pad #5 (+) on the first LED (the other end is left dangling for now).  Then pad #2 of that LED is connected to pad #5 of the next, followed by #2 to #5 of the last (you can add two more LEDs if you want by just repeating this pattern.)  A black wire is connected to pad #2 (-) of the last LED and left dangling.  Make sure these are long enough to reach the terminal strip, and allow proper spacing in the heatsink.  Easy right?

tin-stars.jpgSome hints - use a hot soldering iron (60w at least).  "Tin" the pads first (#2 pad and #5 pad) on each star by heating and coatling with solder.  DO NOT overheat - just get the solder to flow.

Then tin the wires ("tin" means coat the wire/pad with sodler).  Once both are tinned it will be easy to heat up the pad and attach the wire; hold it steady while it cools (almost instant) and pull a little bit to be sure you made a good solder joint).

LED Mounting

LED Mounting - once you've wired up your LEDs it's time to mount them in the heatsink.  The magnifying glass shown above is used to carefully examine the screws to make sure they are not touching the solder joint or an adjacent pad.  This would be bad.  You could use the supplied nylon washer to insulate the screws, but I like to live dangerously.

screws.jpg

First thing you need to do is position the screws in the slots (nuts attached).  Space them out however you want to.  Then it's a simple matter of slipping the LEDs under the screws and tightening them AFTER you put some silicon paste on the heatsink.

silicon-dab.jpg

Put a small dab of paste as shown.  The idea is to create a very thin layer of paste to fill the micro pits and gaps in the aluminum for a good heat bond.  Use a razor blade to smear it and remove excess.

screw-clearence.jpgNow mount the LEDs and make sure the screws are not touching any of the electrical connections (the solder joints or the gold pads).  Before tightening, slide them around a bit to get the silicon paste smeared onto the bottom of the star.

DON'T USE SILICON HEAT GLUE!  You'll never be able to move the LEDs, change configuration, etc.

Other Components - Mount the BuckBullet LED driver (think of it as a "ballast", as in trannies, for LEDs) using a cable clamp.  This LED driver provides a constant current to drive the string of LEDs, whether you are using one or five.  It converts the AC input (the brown wires) to a positive (+) - blue wire, and a negative (-) - white wire.  The blue and white wire are connected to the red and black wires going to the LEDs as shown in the wiring diagram.  The two brown wires go to the 5mm jack and the switch (green wires on the wiring diagram).  

wiring.jpgOne of the brown wires gets connected to the switch (thru the terminal strip) and the other side of the switch goes to the other terminal on the 5mm jack.  (I used blue wiring here 'cause that's what I had).  The other brown wire is connected to the other pin of the 5mm connector.  The third pin on that connector is left unconnected.

Once this is all wired up you can mount the terminal strip to the heatsink, drill some holes in the plastic end caps and mount the 5mm jack and switch. (NOTE: I didn't have you mount the strip before wiring to make it easy to connect the wires).

That's pretty much it!  The heatsink kit includes a fan, but for up to 5 LEDs it's really not needed. 

Double check your wiring.  Then go back and check it again.  Make sure the positive output of the LED driver is going to the positive side of the LED.  Make sure twice.  Make sure the negative side of the LED driver is going to the negative side of the LED.  Make sure twice.  Make sure the negative on one LED is going to the positive of the other LED, on either side of the middle LED - check it three times.

THEN - compare your wiring to the wiring diagram.  If you are sure it matches, plug it in and enjoy!

Filter and Reflector - I'll be testing a couple of LW filters in the coming weeks.  Although the purity of the LW light out of these LEDs is wonderful, they still put out some visible light.  Hoya cleans them up very nicely and is what I have decided to use.

The LEDs are very directional and put out a 105 degree beam.  Most of the UV gets out the front, but for those that want to squeeze every last bit of UV out an aluminum reflector works fine.

I've tested the unit with 5 LEDs driven at 1 amp (higher power than what I show here), a Hoya filter, and a specular aluminum reflector - no fan.  My own display light uses a DC power adapter and a 1A constant current driver.  The AC unit shown here is just a little simpler to build.

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