How do you calculate UV irradiance at the part?

Multiply the lamp's rated peak irradiance by the focal/reflector efficiency factor and by the aging derate percentage. A 2400 mW/cm² rated peak at 0.75 efficiency and 85% aging derate estimates 1530 mW/cm² at the part.

Why is irradiance at the part lower than rated peak?

Rated peak is measured at the ideal focal point with a fresh lamp. Real parts sit off-focus, reflectors are less than perfectly efficient, and lamps lose output as they age — in the example those losses drop 2400 to an effective 1800 before aging, then 1530 after.

What is a good UV irradiance at the part?

It depends on the coating and required cure speed, but higher irradiance drives faster surface cure and better through-cure of pigmented systems. The key is confirming the estimated value clears the coating supplier's minimum intensity spec.

How much does lamp aging reduce UV irradiance?

Medium-pressure mercury and many LED lamps lose meaningful output over life; an 85% derate models a lamp that has dropped 15% from new. Tracking this prevents a slowly dying lamp from under-curing parts unnoticed.

Irradiance vs dose — what's the difference?

Irradiance (mW/cm²) is instantaneous intensity; dose (mJ/cm²) is irradiance multiplied by dwell time in seconds. You need adequate irradiance for surface cure and adequate dose for through-cure, and this tool estimates the irradiance half.

Do I still need a radiometer if I use this calculator?

Yes. The estimate uses assumed efficiency and aging factors that vary by setup. Treat it as a planning number and confirm with a profiling radiometer at the part plane before locking a process spec.

UV Curing calculator

UV Irradiance Calculator

UV irradiance at the part is the actual instantaneous UV intensity reaching the coating, after losses from focal distance, reflector efficiency, and lamp aging cut into the lamp's rated peak. Rated peak is a bench figure at the ideal focal point with a new lamp; the part almost never sees it. Process engineers estimate the real irradiance so they can predict dose and cure margin instead of trusting nameplate numbers. This estimate is a starting point that should always be confirmed with a profiling radiometer pass before it becomes a process spec.

What this calculator does

Estimate the UV irradiance reaching the part from rated lamp output, distance falloff, and reflector / focal-distance efficiency.
Use it before a radiometer is available - for example sizing a new UV station - or to sanity-check whether a measured radiometer number is consistent with the lamp on the spec sheet.
It estimates the UV intensity actually reaching the part by derating rated peak irradiance for reflector efficiency and lamp aging.

Formula used

Estimated irradiance at part = rated peak × focal/reflector efficiency × aging derate %
Confirm with a profiling radiometer pass before committing to a process spec.

Inputs explained

Rated peak lamp irradiance:
Focal / reflector efficiency factor:
Lamp aging derate:

How to use the result

Use it during process design or troubleshooting to sanity-check whether an aged lamp and real focal geometry can still deliver the required intensity.
It is an estimate built on assumed efficiency and aging factors; only a radiometer profiling pass at the part plane gives the true value for a process spec.

Common questions

How do you calculate UV irradiance at the part? Multiply the lamp's rated peak irradiance by the focal/reflector efficiency factor and by the aging derate percentage. A 2400 mW/cm² rated peak at 0.75 efficiency and 85% aging derate estimates 1530 mW/cm² at the part.
Why is irradiance at the part lower than rated peak? Rated peak is measured at the ideal focal point with a fresh lamp. Real parts sit off-focus, reflectors are less than perfectly efficient, and lamps lose output as they age — in the example those losses drop 2400 to an effective 1800 before aging, then 1530 after.
What is a good UV irradiance at the part? It depends on the coating and required cure speed, but higher irradiance drives faster surface cure and better through-cure of pigmented systems. The key is confirming the estimated value clears the coating supplier's minimum intensity spec.
How much does lamp aging reduce UV irradiance? Medium-pressure mercury and many LED lamps lose meaningful output over life; an 85% derate models a lamp that has dropped 15% from new. Tracking this prevents a slowly dying lamp from under-curing parts unnoticed.
Irradiance vs dose — what's the difference? Irradiance (mW/cm²) is instantaneous intensity; dose (mJ/cm²) is irradiance multiplied by dwell time in seconds. You need adequate irradiance for surface cure and adequate dose for through-cure, and this tool estimates the irradiance half.

Last reviewed 2026-05-12.