UV dose is the product of irradiance and exposure time. It answers the question of how much radiant energy a surface actually received during a process – when curing an adhesive, disinfecting a surface or running an ageing test. This calculator takes the measured irradiance in mW/cm² and the time in seconds and returns the dose in mJ/cm² and J/cm².
Its value lies in planning: before a line is set up, you can estimate the exposure time needed for a required dose and whether the available source delivers it. You can equally check whether two installations with different irradiance produce the same dose.
The calculation assumes that irradiance stays constant throughout the exposure and was measured at the position of the workpiece. A dose only becomes binding through a measurement with a calibrated radiometer or dosimeter under real process conditions – Opsytec manufactures and calibrates these instruments in its own laboratory.
If you need the other radiometric conversions, they are collected in the radiometry calculator; if you want to measure the dose rather than calculate it, see measuring UV dose and irradiance correctly.
This calculation is for technical orientation. It assumes an irradiance that stays constant over the exposure time at the measuring position and makes no statement about the effect achieved. Process releases and safety-related assessments must be verified by suitable, calibrated measurements under real conditions.
Fundamentals
Radiant exposure — commonly called UV dose — is the time integral of irradiance. For constant irradiance this simplifies to H = E · t, with irradiance E, time t and dose H. Entering E in mW/cm² and t in seconds gives H in mJ/cm². In SI units, 1 mW/cm² equals exactly 10 W/m² and 1 mJ/cm² equals exactly 10 J/m². The calculator works internally in SI units and rounds only the result.
An adhesive joint is exposed to 50 mW/cm² for ten seconds. H = 50 mW/cm² · 10 s = 500 mJ/cm² = 0.5 J/cm² = 5000 J/m². Conversely, a target dose of 500 mJ/cm² at 50 mW/cm² requires 10 s.
If irradiance varies during the process — because the workpiece passes the source, the lamp warms up or ages — the product E · t is only an approximation; what counts is the integral over time, which a dosimeter measures directly. Dose is also a purely energetic quantity: it says nothing about whether the wavelength matches the photoinitiator, the organism or the test standard. Two processes with the same dose but different spectra can give entirely different results.
Frequently asked questions
UV dose is the radiant energy received per unit area. In practice it is usually given in mJ/cm², in SI units in J/m². 1 mJ/cm² equals 10 J/m². The correct term is radiant exposure; “dose” is the established shorthand.
By a factor of 10: 1 mJ/cm² = 10 J/m². So 500 mJ/cm² is 5000 J/m² or 0.5 J/cm².
Arithmetically it gives the same dose. Whether it also gives the same effect is another matter — that requires the reciprocity law to hold. In UV curing it can fail at very high irradiance because the photoinitiator is consumed locally or oxygen inhibition behaves differently. When in doubt, test the process variant, not just the dose.
The usual causes: irradiance was measured at a different distance or position than where the workpiece sits; the lamp was warmed up during measurement but not during the process; or the sensor evaluates a different spectral range than the source emits.
For a safe design, the lowest value within the working area — it determines where the required dose is reached last. How strongly irradiance varies across the area is shown by the UV LED simulation or by a series of radiometer measurements.
Yes. A dose without the evaluated spectral range is not comparable. Typical statements read “1000 mJ/cm² UV-A (315–400 nm)”. Which range is measured depends on the sensor — see the UV sensor finder.
With a travelling dosimeter that integrates over the pass, or with a permanently installed sensor that monitors irradiance continuously. Both are described in measuring UV dose and irradiance correctly.
Author: Dr. Mark Paravia
Dr.-Ing. Mark Paravia is the managing director of Opsytec Dr. Gröbel GmbH in Ettlingen and heads the accredited calibration laboratory. Following his research on pulsed xenon excimer discharges at the Institute of Lighting Technology at KIT, his current focus is on optical radiation measurement technology. He is vice-chair of the DIN Standards Committee FNL 7 “Optical Radiation” and a member of the DVGW Project Group on UV Disinfection.
