How do you calculate UV exposure time?

Divide required dose by measured irradiance. For 1,200 mJ/cm² at 850 mW/cm², base exposure is 1.41 seconds. Adding a 25% safety margin gives a recommended 1.76 seconds.

Why add a safety margin to exposure time?

UV lamp output falls with age and reflectors foul, so a base time that is exactly on target today will undercure later. A 25% margin, as in the example, buys months of drift before you fall below the dose target.

What happens if exposure time is too short?

The part receives less than its required dose, leaving a tacky surface, poor adhesion, and weak chemical resistance. Undercure is the most common UV line defect and is fixed by increasing time or irradiance.

Can I reduce exposure time by increasing irradiance?

Yes — dose is irradiance times time, so a stronger lamp or closer focus lets you shorten dwell and run faster. But some chemistries need a minimum time regardless, and higher irradiance raises part temperature.

What is a good UV safety margin percentage?

20-30% is typical for production lines. Lower margins run faster but leave little room for lamp decay; higher margins are common on critical adhesion or medical parts where undercure is unacceptable.

Exposure time vs dwell time — same thing?

On a flood or shutter system, exposure time is the shutter open duration. On a conveyor, dwell time is cure-zone length divided by line speed. Both must equal or exceed the recommended exposure to hit dose.

UV Curing calculator

UV Exposure Time Calculator

UV exposure time is how long a part must sit under a UV source to accumulate its required cure dose, and it is the setting you actually dial in on a shutter or conveyor. Process engineers derive it by dividing required dose by measured irradiance, then padding it with a safety margin so day-one settings survive months of lamp decay. It is the practical inverse of the dose calculation: instead of asking how much energy a given time delivers, you ask how much time a target energy demands. Getting this right prevents both slow-running overcure and tacky undercure.

What this calculator does

Solve for the seconds of UV exposure needed to deliver a target dose at a measured irradiance, with a safety margin baked in.
Use it before a static cure or batch fixture run when you know the dose the chemistry needs and the irradiance your lamp is putting out at the work surface.
It computes the base exposure time to reach a required dose at a measured irradiance, then adds a safety margin to give a recommended exposure time.

Formula used

Base exposure (sec) = required dose (mJ/cm²) ÷ measured irradiance (mW/cm²)
Recommended exposure = base exposure × (1 + safety margin %)

Inputs explained

Required cure dose from datasheet:
Measured irradiance at part surface:
Undercure safety margin:

How to use the result

Use it when setting shutter open time, conveyor dwell, or when re-timing a line after a radiometer reading shows irradiance has drifted.
It assumes irradiance is steady during exposure and matched to the datasheet band; it does not account for oxygen inhibition or thick-film depth-cure effects that may need extra time beyond the calculated value.

Common questions

How do you calculate UV exposure time? Divide required dose by measured irradiance. For 1,200 mJ/cm² at 850 mW/cm², base exposure is 1.41 seconds. Adding a 25% safety margin gives a recommended 1.76 seconds.
Why add a safety margin to exposure time? UV lamp output falls with age and reflectors foul, so a base time that is exactly on target today will undercure later. A 25% margin, as in the example, buys months of drift before you fall below the dose target.
What happens if exposure time is too short? The part receives less than its required dose, leaving a tacky surface, poor adhesion, and weak chemical resistance. Undercure is the most common UV line defect and is fixed by increasing time or irradiance.
Can I reduce exposure time by increasing irradiance? Yes — dose is irradiance times time, so a stronger lamp or closer focus lets you shorten dwell and run faster. But some chemistries need a minimum time regardless, and higher irradiance raises part temperature.
What is a good UV safety margin percentage? 20-30% is typical for production lines. Lower margins run faster but leave little room for lamp decay; higher margins are common on critical adhesion or medical parts where undercure is unacceptable.

Last reviewed 2026-05-12.