I am planning to build a disinfection cabinet using UVC radiation. Many of my friends and family work in the health sector and I plan to gift it to them. I am a beginner, i'm sorry if my questions are too easy or stupid. I have been collecting information online about the same and I am pretty confused. The cabinet will have a surface area of 7300 cm^2. I am planning to use 6 X Philips TUV T5 16W tubes with UVC wattage of 4W and irradiance of 45 uW/cm^2 at 1m. The maximum distance between the object and the tube will be 30cm in my case, as irradiance is inversely proportional to distance, I am simply multiplying the irradiance value by 3, so I get 135 uW/cm^2. The total UVC wattage will be 24W(6*4) and irradiance will be 810 uW/cm^2(6*135)(correct me if I'm wrong). I will be covering the interiors of the box with polished aluminium sheets to increase reflectivity.

Different resources suggest different dosages and different formulas to calculate the dosage. Studies based on SARS-CoV-1 suggest a dosage of 7-2410 J/m^2. The IUVA recommends 1-3 J/cm^2 for real world conditions but only 10-20 mJ/cm^2 under controlled lab conditions. Since the cabinet will be closed and effectively almost all UVC radiation will reach the object can I achieve 99.9% deactivation using UVC dosage in order of few hundred mJ?

The next problem is properly calculating the exposure time. I find different formulas that give completely different results.

- According to this study, the exposure time formula is given by : \[ Exposure Time(s) = \frac{UV Dose(J/cm^2)}{Irradiance(W/cm^2)} \] substituting values I get around
**62 minutes**. - According to this Research gate answer, the exposure time is given by : \[ Exposure Time(s) = \frac{Desired UV dose(J/m^2) * 4 * pi * UV bulb distance^2(m)} {UV bulb power(W)} \] substituting values, I get
**23.55 minutes**. - A Youtube video uses the formula, \[ Exposure Time(s) = \frac{Surface Area(cm^2) * Dosage(J/cm^2)}{Power(W)} \] substituting values I get around
**15 minutes**.

As you can see, the differences are huge, idk which is the correct one.

Do I still need a Ballast for the tube if I step down the voltage to the tube's operating voltage?

I'm also planning to include a timer, will any 555 timer or timer relay be enough?

Since, UVC is harmful to humans, I will have to add some mechanism to stop the equipment from being operator if the doors of the cabinet are opened, I planning to use a contact switch.

Thanks