Why is the delivered fraction so low?

Because the losses multiply. A 0.75 reflector, 85% aging and 80% window deliver 51% of the catalogue figure. Each term looks reasonable, which is why the compounding surprises people.

Which loss should I attack first?

The window, because it is free. Cleaning quartz takes minutes and can return 10 to 20% at once. Reflector cleaning and refocus is next; lamp replacement is last because it costs money.

Should I use this page or measure?

Measure whenever a radiometer can reach the part; this page exists for sealed tunnels and bondlines. Where you have both, calibrate the reflector factor so prediction matches measurement.

Does this work for LED arrays?

Poorly. LED output is stable with age, so the aging term barely applies, and LED optics are close-coupled rather than reflector-focused. Use the LED array power density page for those systems.

UV Curing calculator

UV Irradiance at Part Calculator

Predict how much of a lamp's rated output reaches the part. Enter the rating, reflector efficiency, aging derate and quartz transmission; use it where no radiometer can reach.

What this calculator does

Predict the irradiance reaching a part by working down the reflector, lamp age and quartz losses.

Formula used

After reflector = rated irradiance × reflector efficiency
After aging = after reflector × aging derate ÷ 100
At part = after aging × window transmission ÷ 100
Lost to aging = after reflector − after aging
Fraction delivered = reflector × aging × window

Inputs explained

Rated Peak Lamp Irradiance: Manufacturer's rated peak output at the focal distance, new lamp.
Reflector Efficiency Factor: Fraction of rated output the optics place on the part.
Lamp Aging Derate: Output remaining as a percent of new.
Quartz Window Transmission: Percent passing any quartz between lamp and part.

How to use the result

Best suited to estimating irradiance where no radiometer can reach, sizing a lamp for an unbuilt machine, deciding between a cleaning job and a lamp.
A prediction, not a measurement; every term is uncertain and they multiply. Window transmission is not spectrally flat; solarized quartz cuts short wavelengths harder. Working distance is buried in the reflector factor; the distance page models it directly.

Common questions

Why is the delivered fraction so low? Because the losses multiply. A 0.75 reflector, 85% aging and 80% window deliver 51% of the catalogue figure. Each term looks reasonable, which is why the compounding surprises people.
Which loss should I attack first? The window, because it is free. Cleaning quartz takes minutes and can return 10 to 20% at once. Reflector cleaning and refocus is next; lamp replacement is last because it costs money.
Should I use this page or measure? Measure whenever a radiometer can reach the part; this page exists for sealed tunnels and bondlines. Where you have both, calibrate the reflector factor so prediction matches measurement.
Does this work for LED arrays? Poorly. LED output is stable with age, so the aging term barely applies, and LED optics are close-coupled rather than reflector-focused. Use the LED array power density page for those systems.

Last reviewed 2026-10-01.