DIY: Lego UV LED Flashlight.

This is a super fun and easy project that you can do with your kiddos in no time, with minimal tools, and parts that are very cheap online. I provide a parts list, a 5 1/2 minute video tutorial, reference images, and a basic electronics lesson, as well as my own design for building this flashlight. I highly encourage modifications. My design is… meh, at best. But this will hopefully give you a good basic understanding of how to make these for yourself. And don’t stop with a flashlight either, imagine Dollhouses, Figurine Holders, Stop Motion, or anywhere a cool, colored LED light might be needed. If you are new to electronics, just refer to ohm’s law below to make the wire runs longer. I will keep saying this until you loathe me… and / or know ohm’s law by heart. Also, please feel free to leave any comments or questions on this page. If you need to tell me that this sucks, please email me instead 🙂 First, the video. It makes it easier if you PAUSE to read the still photos with the written instructions, as I did not leave them running for too long. You obviously don’t have to watch, but it does give an easier timeline of events. Enjoy!

Homemade UV LED Lego Flashlight
Ohm’s Law Triangle

So, with this basic setup, you can come up with all kinds of various lighting ideas for projects or just for fun. I will post some still photos I have from the video below for reference. Again, if you have any questions, I would be happy to answer them. There will be a few more posts on the way, in which I will show you how to make snap together circuits, and other cool LED projects.

Parts Needed

  • Legos, Mega Bloks, etc…
  • One 5MM UV LED
  • Two AAA Batteries
  • One AAA X 2 Battery Holder With Attached Wires
  • One SPDT (single pole / double throw) On-Off Slide Switch
  • 22 AWG Wire ( five feet or so )
  • Super Glue
  • Hot Glue / Hot Glue Gun
  • 22 AWG Butt Connectors
  • Isopropyl Alcohol ( GREAT Solvent, for removing super glue if needed )

I do NOT use resistors, as the resistance from the wires, switch, and LED for this project fall within parameters to ensure the correct brightness for the LED. Just keep reading ohm’s law 😉 you’ll get it. All of these components are bought very cheaply online from Amazon or one of my favorites,, and can be searched for using the descriptions I used above. I AM NOT earning commission from them… Yet. Again,
pause through the instructional text if you need to.

SPDT On/Off Slide Switch


AAA X 2 Battery Holder

Extra Illustration And Description

How To

If you didn’t watch the video that’s fine, the instructions are pretty simple. You probably want to put together your circuit “guts” first, then build your Legos around it, or place the circuit into your project with super glue, hot glue, or whatever means you choose.

Example Of The Circuit “Guts”

The above picture shows the whole circuit put together. Power Source ( batteries ), LED, SPDT On / Off Slide Switch, Wires, and a Resistor ( oops ), I couldn’t find the exact picture I used for this project so I had to use another one, as I did not want to pull the flashlight apart to take a picture for you. And this particular circuit happened to have a resistor in it. Maybe we can use this for a learning lesson. If you add any type of resistance in the circuit it will only dim your light. End of lesson. Read up on Ohm’s Law. If you actually do want to dim the light and make your batteries last longer, then go ahead and add a small resistor ( 330 Ohm’s or so, just play around with it ), otherwise you do not have to. As mentioned earlier, the light shines perfect with just the switch, LED, battery holder, and wires. ALL of these things add resistance to the circuit, as they ALL consume a small amount of electricity. I will definitely post a better electronics lesson in another post, but for now we’re just learning how to put this simple thing together. K.I.S.S. Keep It Simple Sailor!

Start by connecting the butt connectors to the wires on the battery holder. Place the open ( copper ) wire into the butt connectors until it comes into contact with the metal tubes in the connectors, and just crimp down on the plastic until the wire is tightly secured in it. The picture below shows a very beefed up way to do it. You do not need to do that for this project, but it’s good to know how to properly do it as well. Also, I am not using heat shrink butt connectors, just hard plastic ones that WILL Crack if you use excessive force.

Photo Courtesy Of Amazon. Thanks Y’all
LED Breakdown. Photo belongs to:

The only REAL technical aspect of this, is to make sure you have your polarity ( + – ) correct when hooking the LED to the wires. As shown in the picture above, the ANODE is the positive lead coming from the LED, and the CATHODE is the negative lead ( wire ). The ANODE ( positive ) is almost Always Longer, this helps for quicker identification.

Now you have your circuit built. You can shove it inside of a project of your choice, or build around it. Have fun with this, and more to come. If you have any comments, please feel free to leave them. Might as well share and like the video also 🙂


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