Handheld UVC LED disinfector

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.

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.

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.

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.

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.