☢️ Warning

Short-wave UV light is harmful to humans. In addition to causing sunburn and (over time) skin cancer, this light can produce extremely painful inflammation of the cornea of the eye, which may lead to temporary or permanent vision impairment. It can also damage the retina of the eye. For this reason, the light produced by a germicidal lamp must be carefully shielded against direct viewing, with consideration of reflections and dispersed light.

🛠 Components & construction

Ballast: Philips HF-M BLUE 124 SH TL/TL5/PL

Tube: Phillips UVC 254nm 18W

Box consists of aluminium base plate and acrylic (PMMA). Walls are internally covered with tinfoil to protect it from UV-C (it would deteriorate the plastic over time) and reflect the UV-C back to the objects for high efficiency. All fixtures are 3D printed from PETG, which is reasonably UV resistant.

🧮 Calculations

Tube: Phillips UVC 254nm 18W

UV-C power of the tube is P(UVC) = 5.5W

Maximal distance of the object from the tube is 12cm

Calculating the light-front (approximate area of the light surrounding the lamp at particular distance)

w (diameter of the lamp) = 3.7cm

r (distance from the lamp) = 12cm

h (length of the lamp) = 19.5cm

Light-front area calculation by Wim

$$ S=2\pi h(\frac{w}{2}+r)+4\pi r^2+w^2+4\pi rw+4hw = 6227.81cm^2 $$

Calculating irradiance at 12 cm:

$$ E_{12cm} = \frac{P_{UVC}}{S} = \frac{5,5W}{6227.81cm^2} = 883.13 \frac{\mu W}{cm^2} $$

Dosage required to kill SARS-CoV-2 is H = 2-5 mJ/cm2 (2000-5000 µWs/cm2) (source)