Handheld UVC LED disinfector

Using the highest power germicidal LEDs currently available,
paired with lithium ion batteries in a portable footprint.

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UVC LEDs have been in development for years as an ideal replacement for fluorescent bulbs because of their resistance to shock, temperature, and frequent cycling. The idea of a solid-state, long-life, mercury-free light capable of destroying any pathogen once seemed like science fiction. High-powered models are now available, and I couldn't wait to try them out!

A pair of Lithium-ion batteries and a converter power the unit. Heat sinks and a fan keep the LEDs cool, while an Arduino controller provides the interface and safety features. The LEDs emit true germicidal wavelength, unlike some devices on the market which actually emit UVA ("black light").

Portable UVC lights are useful on masks, hats, shoes, durable medical equipment, fabrics, food, and other objects that aren't easily wiped down or have recessed surfaces. The ideal range for fast disinfection is about 2 inches (2.5cm), though it will illuminate bleached objects from several feet away.

The purpose of this project was to experiment with the latest models of UVC-LEDs in a portable format and explore different controller, driver, power, and thermal solutions. The high powered LEDs I selected are intended for ceiling-mounted arrays like the one shown below. What would it take to put a couple of these lights into a handheld box? Let's find out!

[Array with frame and heat sink. Silica UVC lens array by LEDiL of Finland.]

Ultraviolet-C sterilizes by destroying thymine bonds in DNA, rendering microbes unable to survive or replicate. LEDs are available throughout the germicidal range of 250-280nm. The ideal wavelength depends on the type of pathogen being targeted, but the average peak for maximum effect is at 265nm (mercury bulbs peak at 257nm).

[References provided at the end of this section.]

Safety is a recurring theme throughout this project due to the use of high-discharge Lithium batteries, hot power LEDs, and UVC emissions. Battery power is connected through a mechanical toggle switch to ensure that power is completely disconnected when the device is not in use. 

An Arduino controller monitors the temperature and current consumption. The LEDs are turned off automatically in the event of a fault such as overheating, open or short circuit, or buttons being inadvertently pressed in a pocket or purse. The Adafruit M0 was chosen for its many I/O lines and capability for the task (it also behaved more reliably than some Arduino boards I've used). The controller and firmware could accommodate larger arrays with little or no modification, along with any additional sensors.

The unique enclosure is held by its rubberized sides and pointed away to prevent direct exposure. LEDs are mounted facing downwards through the bottom with enough clearance to protect the integrated 60° lenses, which are made of special quartz. UVC-transmissive windows and lenses are quite expensive and about 85% transmissive, so no additional optics are used here.

Rather than using one of the many current-limiting driver circuits available, I opted for the old fashioned method of using a current limiting resistor. I searched extensively but found only two drivers (unavailable/costly) matching the necessary combination of voltage, current, step-up, and total power handling.

It was an opportunity to exploit a unique feature of these LEDs: they can be driven past the base specification if appropriate thermal measures are taken. [Datasheet nominal is 350mA, with linearly increasing output to an absolute maximum of 800mA. Product lifespan is reduced when approaching the upper limit.] In other words, they will tolerate "excess" current if an appropriate level is chosen for device lifespan and thermal considerations (500mA is suggested in the datasheet).

A Meanwell DC-DC converter is used to produce the necessary voltage. Though rated for 15V, its output can be adjusted with a single resistor connected to the "Trim" pin. This provides a way to compensate for variations since even identical LEDs can have slightly different forward voltages (5-7.5V each). The converter also has a few built-in safety features and is not prone to the flickering effect or failure rate of buck/boost drivers.

A Sunon UF3H3-710 fan is used to circulate air through the enclosure. This model had the highest CFM and air pressure of all miniature fans available - and just enough for the task. There is about 1mm of clearance between the LEDs and the bottom of the enclosure, allowing a gap for air to be drawn in around the heatsinks and out through the front panel. This setup is also less likely to draw excessive dust and debris inside.

High-capacity 18350 batteries (KeepPower UH1835P) will last for about 1-2 months of casual daily use and recharge in approximately half an hour. In lieu of an internal USB charger, I chose an external smart charger (XTAR VC2S or VC4S) which is faster, safer,...

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  • 2 × LST1-01G07-UV01-01 STARBOARD, XST-3535-UV, 275-286N
  • 1 × UF3H3-710 Fan Tubeaxial 3VDC Square - 17mm L x 17mm H Vapo-Bearing 0.575 CFM
  • 1 × GRB213B03BB Rocker Switch
  • 1 × MMP0120ABKP (or similar, must be as short as possible) 12mm diameter momentary pushbutton switch (SPST)

View all 37 components

  • Application note and sterilization data

    MarkC10/16/2021 at 18:24 0 comments

    This is an excellent application note from Luminus, manufacturer of the UVC-LEDs used in this project. 

    UV-C LEDs for Disinfection and Sterilization

    In their experiments, inactivation of  >99.999% was achieved in 20 seconds of exposure at a distance of 1cm. One of the goals in this project was to shorten the required exposure time, and if possible, increase the exposure distance to a more practical level without decreasing sterilization effectiveness.

    The current used in this project is higher than in the note's experiments (500mA vs 350mA) to increase the output by about 40%. These LEDs have lenses which are focused onto a smaller area (60° vs 130°) for higher beam concentration. Manufacturers offer these devices in a range of power levels, with and without lenses.

    The ideal result is >90% inactivation of microbes within 10 seconds at a distance of 2-5cm.

  • Showdown!

    MarkC10/05/2021 at 18:35 0 comments

    Here's a side by side comparison to a store-bought model which uses a small fluorescent bulb. A pair of phosphorescent indicator cards will help expose the ultraviolet light for comparison.

    UVC light is invisible to cameras and human eyes, what we are seeing is the very edge of the spectrum emitted by these lights which falls into the visible range (and some bleaches which will partially convert UVC to white light). Human corneas and nearly all artificial optic materials will absorb these wavelengths.

    [Chart below is for illustrative purposes only] 

    The fluorescent bulb (left) emits a visible 'ice blue' color over a wide area, but the LEDs (right) emit noticeably more intense UVC. Images were taken with each light at a 2 inch distance.

  • Custom PCB and other parts

    MarkC10/03/2021 at 13:43 0 comments

    For anyone interested in assembling this project, I have a few circuit boards available for purchase since the prototyping service provided several of them. They are commercially made with high quality coatings, solder masks, and silkscreen labels for all the components. The firmware, custom battery clips, and machined heat sinks can also be provided.

  • UVC safety

    MarkC10/03/2021 at 13:40 0 comments

    A reminder that UVC light can be harmful for the eyes and skin. Use protective eyewear (or close your eyes), point the light away from eyes and skin. Eyeglass lenses will block UVC, but do not protect the eyes from all angles.

  • Alternative battery setup

    MarkC10/02/2021 at 16:32 0 comments

    Here is a 2-cell 18350 battery caddy that may be used instead. This was the original setup before I fabricated custom contact pieces. This caddy is a tight fit and the edges should filed or sanded as needed. It slides into the compartment upside down at an angle. Keystone Electronics (part #1102) available from major parts distributors.

View all 5 project logs

  • 1
    Chassis preparation

    The enclosure used for this project is a Hammond 1553BBKBAT. To begin, holes for the OLED and switches are milled (or drilled) into the top half.

    Next the bottom half is milled in several areas to make space for all of the internal components. Yes, it's a tight squeeze once everything is installed!

    • Holes for the UVC LEDs
    • Grooves to accommodate LED mounting screws, washers, and wires
    • Removal of 4 PCB mounting posts 
    • Removal of the battery compartment flap
    The completed top piece

    Top piece with the switches installed, each has a JST-PH connector soldered on with heat shrink tubing for additional insulation. In this view the pushbutton switch is on the left, and the power switch is on the right.

    Bottom half completed. The battery contacts seen here will be added in a later step.

    It took several attempts to make the grooves large enough for the heatsink/LED screws and washers. Additional grooves were made for the LED wires.
  • 2
    Battery contacts

    Two battery contact holders are milled out of 1/4" thick ABS plastic. Grooves and channels are made to accommodate contacts and wires.

    Identical format is used for both sides.

    Contacts are installed. The spring-like negative contact is pushed into a slot at the end of each piece, and the flat positive contact is pushed into a top-facing slot. One side has a JST-PH connector soldered on, and the other side contains a fuse.

    Both pieces installed into the battery compartment with 2-sided tape.

  • 3
    Printed circuit board (PCB)

    A custom PCB fits snugly into the enclosure. Notice the side slots which hug the mounting posts. I'll be posting more details about the circuit at a later time.

    Rather than etching the boards myself, I had them commercially made by DKRed and it was definitely worth it. They have high quality coatings, solder masks, and silkscreen labels for all the parts.

    Components are soldered onto the circuit board. The Arduino board is installed with only the necessary pins populated, this frees up space on the main circuit board and reduces the amount of soldering needed. 

    The OLED connector is removed from its own board to provide clearance, and soldered onto the PCB. A cable included with the OLED is cut into half and soldered directly onto the OLED circuit board. An equivalent 4-pin JST would have occupied more space. Alternatively, the display can be hard-wired to the PCB with standard ribbon cable (paying attention to signal polarities).

    (This one is smaller than a 4-pin JST. Be careful not to damage these connectors as I have no idea where to find a replacement.)

View all 7 instructions

Enjoy this project?



Martin wrote 09/30/2021 at 11:36 point

"Black lights" do not use not UV-B but UV-A. Around 400nm. UV-B can cause sunburn and damage to the eyes.

  Are you sure? yes | no

MarkC wrote 09/30/2021 at 11:46 point

Thank you Martin, I'll make the correction. I probably rushed through that section and confused the two.

  Are you sure? yes | no

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