The UV dose represents the product of the rate of energy emission (lamp intensity) and the time the organisms are exposed to the germicidal energy at 254 nm. This can be expressed by the equation: Dose = intensity x time (d=It)

The UV dose represents the product of the rate of energy emission (lamp intensity) and the time the organisms are exposed to the germicidal energy at 254 nm. This can be expressed by the equation: Dose = intensity x time (d=It)

• A. Dose = intensity × time
• B. Dose = time × flow
• C. Dose = energy × time
• D. Dose = intensity + time

Answer: (A)

UV dose is the energy delivered per unit area to the microorganisms, so it grows with how strongly the lamp is delivering energy (intensity or fluence rate) and with how long the organisms are exposed. Multiply the UV fluence rate by the exposure time to get the dose: Dose = intensity × time. This makes sense because the energy arriving per square centimeter accumulates over time; doubling the intensity or doubling the exposure time will both double the total energy per unit area, assuming all else is constant. The units work out too: intensity in milliwatts per square centimeter times time in seconds gives millijoules per square centimeter, which is the common dose unit. The other formulations aren’t correct because dose is not a sum of quantities, nor is it defined by flow in this simple context, and it isn’t simply energy times time (that would be total energy, not energy per unit area).

UV dose is the energy delivered per unit area to the microorganisms, so it grows with how strongly the lamp is delivering energy (intensity or fluence rate) and with how long the organisms are exposed. Multiply the UV fluence rate by the exposure time to get the dose: Dose = intensity × time. This makes sense because the energy arriving per square centimeter accumulates over time; doubling the intensity or doubling the exposure time will both double the total energy per unit area, assuming all else is constant. The units work out too: intensity in milliwatts per square centimeter times time in seconds gives millijoules per square centimeter, which is the common dose unit.

The other formulations aren’t correct because dose is not a sum of quantities, nor is it defined by flow in this simple context, and it isn’t simply energy times time (that would be total energy, not energy per unit area).