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# For the GEEKS in you - How to calculate the UVC dose for given UVC lamp?

The Irradiance formulas for UV Discharge lamps:

A) For a large distance to the lamp we get:
*The irradiance = (Total Radiation flux (W)/ π2.a2 ——- For (a >> L)*

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*B) At shorter distances the irradiance:
*The irradiance = (Total Radiation flux (W)/ 2 π.a.L ——- For (a < 0.5 L)*

L is arc length of the lamp which is distance between 2 arcs inside lamp tube

- which is 3.35” (85mm) for 4 Watt lamp

a: Is the perpendicular distance between surface & Bulb*
*

Eg: For a 4W Lamp The Total Radiation flux is 0.9 w At 1 meter the irradiance would equal to 9.13 uW/cm2

At 1"/ 2.54cm the irradiance would equal to 6.64 mW/cm2

At 4” (10.16cm) >>>>> the irradiance would equal to 884 uW/cm2

Note: Don’t forget the Mercury UV lamps operate at 254nm wavelength, while the Peak Germicidal effect occurs at ~264nm so you need to correct for the radiation generated by your bulb at 254 nm, which is approximately at 85% of the maximum germicidal effect. So derate you’re calculated irradiance by 15%.

For UVC LEDs 265-275nm this difference is negligible
with thanks to **Mark Qandil** on **Jul 01, 2020**

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