How do you calculate UV LED array power density?

Divide total UV optical power by the array's effective emitting length, then multiply by a thermal/aging derate. With 180 W over 12 in at a 90% derate, nameplate density is 15 W/in and effective density is 13.5 W/in.

Why derate the nameplate power density?

Manufacturers spec optical power on a cold, new array. At operating temperature and after hours of use, LED output drops. The derate — 90% in the default — turns the 15 W/in raw figure into the 13.5 W/in the part actually receives.

What derate factor should I use for a UV LED array?

A new, well-cooled array might hold 92-95%; a mature array or one running warm can fall to 80-88%. Use 90% as a planning default and tighten it with radiometer data over the array's life.

Is power density the same as UV dose?

No. Power density (W/in or W/cm²) is intensity; dose (mJ/cm²) is intensity times exposure time. On a conveyor, dose falls as line speed rises even though power density is unchanged — you need both to guarantee cure.

Why W/in instead of W/cm²?

W/in is a linear density handy for comparing conveyor-width arrays and matching an array to a line. Peak irradiance in W/cm² at the part depends on working distance and optics; W/in is a normalization step, not the final irradiance at the substrate.

My array cures fine when new but not after a year — why?

LED output decays with hours and heat. If your effective derate has dropped from 90% to, say, 78%, effective density falls proportionally and can slip below your chemistry's threshold — this tool quantifies that drop so you can plan replacement.

UV Curing calculator

UV LED Array Power Density Calculator

UV LED array power density converts an array's total UV optical output and emitting length into linear power density (W/in), then derates it for the thermal and aging losses that separate nameplate specs from what the part actually sees. UV process and equipment engineers use it when specifying or troubleshooting UV LED curing on conveyors, inkjet presses, and coating lines. It matters because LED makers quote optical power on a cold, new array, but real cure happens on a warmed-up array that's logged thousands of hours — and cure is driven by the density delivered at the substrate, not the nameplate. Getting effective W/in right is the difference between a process that holds and one that slowly drifts into under-cure.

What this calculator does

Calculate UV LED array optical power density (W per inch of array length) - the spec that lets you compare LED arrays head to head independent of array length.
Use it during LED array sourcing or retrofit sizing to compare quotes from different vendors, or to scale a known-good design to a new product width.
It computes effective UV LED power density at the part by dividing total optical power by emitting length for nameplate density, then applying a thermal and aging derate.

Formula used

Nameplate density = UV optical power ÷ array length (W/in)
Effective density at part = nameplate × thermal/aging derate

Inputs explained

Total UV optical power of the LED array:
Effective emitting length of the array:
Thermal and aging derate factor:

How to use the result

Use it when sizing a UV LED array for a line speed, comparing arrays, or diagnosing why an aging array no longer fully cures at its rated setting.
It gives linear power density along the array, not peak irradiance (W/cm²) at the working distance — actual cure also depends on emitter-to-part gap, focusing optics, and beam spread, which this does not model.

Common questions

How do you calculate UV LED array power density? Divide total UV optical power by the array's effective emitting length, then multiply by a thermal/aging derate. With 180 W over 12 in at a 90% derate, nameplate density is 15 W/in and effective density is 13.5 W/in.
Why derate the nameplate power density? Manufacturers spec optical power on a cold, new array. At operating temperature and after hours of use, LED output drops. The derate — 90% in the default — turns the 15 W/in raw figure into the 13.5 W/in the part actually receives.
What derate factor should I use for a UV LED array? A new, well-cooled array might hold 92-95%; a mature array or one running warm can fall to 80-88%. Use 90% as a planning default and tighten it with radiometer data over the array's life.
Is power density the same as UV dose? No. Power density (W/in or W/cm²) is intensity; dose (mJ/cm²) is intensity times exposure time. On a conveyor, dose falls as line speed rises even though power density is unchanged — you need both to guarantee cure.
Why W/in instead of W/cm²? W/in is a linear density handy for comparing conveyor-width arrays and matching an array to a line. Peak irradiance in W/cm² at the part depends on working distance and optics; W/in is a normalization step, not the final irradiance at the substrate.

Last reviewed 2026-05-12.