UV LED Torch




In this tutorial, I will show you how to construct a simple, cheap, and powerful Ultra-Violet Torch for all your UV illumination needs. This project is beginner friendly and requires only basic soldering skills.
Lets get started!

Step 1: What You Will Need

Components you will need for this project include:

- x2 Ultra-Violet LED's. (I purchased mine from Radio Shack for under 2 bucks.)
- x1 100-Ohm Resistor (Again, from Radio Shack. 99cents for a pack of 5.)
- x1 DEAD 9v Battery (or purchased 9v battery clip)
- x1 WORKING 9v Battery
- Pliers
- Basic Soldering Equipment.

Step 2: Extracting the 9v Terminal Clip

Using your pliers, Carefully peel the shell of the 9v back, and expose the cells inside the protective covering. In this step, we are going to extract the terminal clip, which will be the base of our project.

Step 3: Warm Up the Soldering Iron- Construction Begins

The first part of this step includes determining the Negative (-) contact on our freshly extracted clip. When dealing with 9v batteries, the large contact is Negative, and the small contact is Positive. But beings that the terminal clip is going to connect to our working 9v battery, the contacts for the clip we extracted are reversed. The small contact connects into the large contact, and vise versa. Identify the Negative (-) contact on the clip we have just extracted (the small contact of the two) and begin soldering the 100-Ohm Resistor to its corresponding contact point on the back, trimming the resistors leads as needed. Refer to Picture.

-Note: Be generous with the amount of solder to get the resistors lead firmly connected. I had a hard time getting it to stick well with minimal solder. Adding more will do the trick.

Once the Resistor is secured, bend it downward also bending the un-soldered lead parallel to the resistor. This keeps the circuit organized and compact.

Step 4: Soldering the LED's

Once you've determined the Negative terminal and have firmly soldered the resistor to the contact, and bent the resistor in a organized manner, we will now start soldering the LED's.

First, with one LED, trim the POSITIVE (+) lead to about 1/4"
Next, with the other LED, trim the NEGATIVE (-) lead to 1/4" as well.

Once you have done this, you'll want to bend the shortened contacts both outwards at a 90� angle.

Last, solder the two shortened contacts together.
Refer to Picture

Step 5: Putting It All Together

Once your LED's are soldered together, and your resistor is soldered and bent strategically, you may now trim the un-soldered LED leads and solder them to their correct terminals. The LED with the un-soldered NEGATIVE terminal is soldered to the un-soldered resistor lead. The LED with the un-soldered POSITIVE lead is soldered directly to the positive contact, or the "big" contact corresponding on the opposite side.

-Note: If you look carefully into an LED, connected to the leads are two pieces of metal. One piece is significantly bigger than the other, that lead would be NEGATIVE (-). Leaving the smaller piece POSITIVE (+).

Step 6: Let There Be Light!

Your finished project should look something like the picture below, and easily clip onto a working 9v battery for a powerful, long lasting UV LED!

If UV isnt your taste, you can duplicate this same project using different colored LED's, but that would require a different resistor suitable for your LED.
How do you find out which resistor is right for the LED you want to use?
When buying LED's, specifications are usually given for the average operating voltage, and mA to illuminate the LED. With those values, you can plug them into a simple online calculator that will give you the best resistor for your needs. This calculator can be found here: http://led.linear1.org/led.wiz

Question: "I have 2 LED's, but they are salvaged, therefor I don't know their operating values to plug into the online calculator."

Answer: A good rule of thumb is not to run a LED on any more than 3v WITHOUT A RESISTOR unless specified to have a higher operating range. For LED's with unknown voltage and mA values, "diode forward" or operation voltage should be 3, and 20mA should work just fine.



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    22 Discussions

    How many uses does it have? I was getting ready to chuck out a stack of ex-smoke detector 9-volt batteries, thanks heaps, I am going to strip off the connectors now. I bet they also make good cable joiners for projects

    3 replies
    Lateral Thinkernruegs

    Reply 9 years ago on Introduction

    Seeing I live in State Housing, I will ask the "landlords" electricians for more 9 volters, it is political if a state tenant dies because the smoke detector does not work so at great cost, when you call, they sent somebody to put in a new battery.

    But heaps people then remove them, for powering radios etc, putting back the flat battery from the radio, which came from the detector in the first place too.

    We are going to mains powered now, using 9 volters as back up.

    Maybe 6-7 years ago, they tried long life lithium 9-volters, the batteries were preinstalled, the detector sealed up by the supplier. However, within months of mine being installed, I needed new batteries.

    I made inquiries, and I was told that all the sealed detectors had been railed in shipping containers from Auckland down to Wellington, during a very hot summer, they overheated, and all were screaming out during the trip. Under express freight, it was about 8 hours, more likely it was a broken trip over two days.

    A lot of people were disappointed, they thought these lithium batteries would power their radios for 10 years, NO, they had a shelf life of 10 years, the smoke detectors used so little power, it was always the shelf life of a 9-volter that ran out first.

    Every year, first cold snap of the Winter, the low battery warning beeps go off everywhere.

    MarkF74Lateral Thinker

    Reply 3 years ago

    State housing and your stealing batteries from smoke detectors. What a low life!! You should be greatfull for a hand up from my tax dollars you punk. Go get a job and stop being a leach.


    4 years ago

    I made one similar a few days ago. Except I used white leds and also put a momentary switch/button. Tho I did use the same resistor...

    Also here's a good way to figure what resistor to use without the led calculator.

    9v (power supply)- 7v (led voltage drop)= 2v (leftover voltage)÷0.020 (amperage)= 100ohms (resistor value)

    Here's my torch.

    14 12:15 PM.jpg14 12:15 PM.jpg

    6 years ago on Introduction

    Sorry for being a burden I am n00b when it comes to electrical components. But I have a few questions that I would like to get some help with.

    Is there anyway to make it so that it flashes?

    Can I use smaller batteries(a few button cells I need to use it in a very small space)?

    Lastly, I want to have the whole thing sealed in a waterproof container/ substance (for a fishtank?) but still be able to toggle it on/off and flash/ steady light, any ideas thoughts would be greatly appreciated.

    man i wish we had radio shack in canada...all we get now is the source which doesn't have many electronic components and the ones they do have are overpriced :P

    2 replies

    Reply 6 years ago on Introduction

    thats all radio shack is anymore, theyre changing a little bit, but its still 4 bucks or so for 2 LEDs... your probably better off going on ebay, you cna get deals like 600 LEDs for 4 bucks.


    Reply 9 years ago on Introduction

     no kidding, eh? i miss Radio Shack. I have to travel all the way the the states to buy stuff there.

    Go to taydaelectronics.com they have cheap shipping and cheap products.

    I am never going to purchased any thing from Radio Shack ever.


    8 years ago on Introduction

    Mine worked really well =). For some reason the Enercell battery is brighter than the Duracell.

    Adam Manick

    8 years ago on Introduction

    UV leds are the best kind of led to get glow in the dark items to glow


    8 years ago on Introduction

    Nice, I'm going to make a few of these with normal LEDs for thinks like power outrages! (I had to deal with a 30 hour long power outage a few days ago, next time, ill be prepared!) :)

    Dream Dragon

    8 years ago on Introduction

    Beautifully assembled project, well documented and informative instructable. Thank you for sharing it.


    9 years ago on Step 1

    Thanks for adding the link to the LED calculator. This instructable has been very helpful.

    dj whatever

    9 years ago on Introduction

    you can take an led flashlight and just change the regular leds with the uv leds..  much more powerful.. i think.. very good instructable though..