Introduction: UV LED Glow-in-the-dark Decal Charger

This battery powered UV LED light helps to keep the glow-in-the-dark decals made of photoluminesent vinyl charged and always glow brightly in the darkness.

I have a friend who is a firefighter. He and his buddies wear helmets with glow-in-the-dark vinyl decals that display their station number and names on the front and back so they can locate and identify each other in the total darkness often filled with smoke. The decals made of photoluminescent vinyl need to be energized by exposing to a light source periodically in order to retain the ability to glow in full brightness. However, the gears are often stored in the metal locker at the corner of station house or inside fire truck and barely get any light all day, this makes the glow-in-the-dark decals almost useless. Also there's no power source inside the locker, so my friend wishes to have something that is battery powered to keep the decals on the helmet fully charged all the time.

This portable UV LED "decal charger" solves the problem by periodically illuminating the decals with UV light thus keep them always glow in the full brightness in the dark, and helps to improve first responder's safety.


Step 1: How It Works

The photoluminescent vinyl film is widely used for safety sign and egress marking, graphics and stickers of all type. It is a vinyl film coated by special photoluminesent material which absorbs and stores photons (i.e. light particles) from light source and the light energy stored is released as visible light in the darkness. It is best charged by the UV light or sun, other electric light sources such as fluorescent/incandescent lights or flashlights can also be used. Typically a full charge can be achieved by:

  • 3-4 minutes of ultraviolet (black) light, or
  • 7-8 minutes of direct sunlight, or
  • 21-23 minutes of fluorescent light, or
  • 24-26 minutes of incandescent light

Glow lifespan is typically a few hours, and may vary due to a) proximity to charging light source, b) angle of exposure to source, and c) brightness of source lamp.

For this project two UV light bars each consists of 12 395 nm UV LED are designed to illuminate both the front and back of the helmet simultaneously. The light bars are controlled by an programmable electric timer with built-in real time clock and up to 16 independent ON/OFF schedules. This provides the flexibility to program the device according to the shift schedule and preserve the battery power. The entire unit is powered by a Ryobi One+ lithium tool battery pack which is easily available. If one set up the program to charge the helmet for 15 minutes every hour, a 4 Ah Ryobi P108 battery can last entire week.

Step 2: Make 3D Printed Parts

I printed all the parts with PTEG and 30% infill, use support where appropriate.

Step 3: Wiring and Assembly

First cut 2 strips of the UV LED each with 12 LEDs from the roll, and solder the pigtail wire with the male DC connector to one end of the LED strip. Use the self adhesive backing to mount the LED strip into the slot on the 3D printed light bar, secure the wire with a piece of zip tie. Note that the light bar is designed in pairs, one with the power cable on the left hand side and another one on the opposite end. This will help the wire management in the crowed lockers. Also install two magnets on the back of the each light bar by inserting them into the round recessive mounting holes.

A fully charged Ryobi One+ tool battery is 18V, and the programmable timer and the LED strip work at 12V. I used a DC-DC step down buck converter covert the 18V to 12V. Before connect timer, use a multimeter and adjust the output voltage of the buck converter to 12V first by turning the potentiometer on the buck converter.

The entire wiring and assembly is straightforward. Please refer to the pictures for details.

  1. Connect the keystone battery clips to the input of the buck converter, then install the clips on the 3D printed connector tower. Pay attention to the (+) and (-) of the battery.
  2. Connect the output of the buck converter to the input of the programmable switch, also connect the 12V (+) to the input of the power relay
  3. Connect the output of the power relay as well as the 12V (-) to the female panel mounted socket.

Step 4: Use the UV LED Decal Charger

The decal charger is very easy to use. Simply program the charger to turn on/off the UV LED at desired time and duration, then place the LED UV light strip in the locker close to the helmet. There are two magnets on the back of the UV LED strip to help secure it.

I got a text message a few weeks after my friend put the light in use, here it reads:

"We finished our fire classes two weekends ago and part of the training is a controlled burn.. two fellow fire fighters told me they couldn’t see anything and had no idea where I was and then they saw my helmet glow!! Awesome Stuff!!"

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