UV Curing calculator

UV Irradiance Calculator

Engineers laying out a new UV station or evaluating a vendor lamp often need an irradiance estimate before they can put a radiometer on the line. This calculator combines the lamp's rated peak irradiance, an efficiency factor that captures focal distance and reflector condition, and a derate for lamp aging to land on a defensible mW/cm² at the part — close enough to size dose math and validate a quote.

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.
  • Estimates mW/cm² at the part from the lamp's rated output, an efficiency factor for focal distance and reflector condition, and a derate for 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 irradiance: From the lamp data sheet at the rated focal distance and the relevant UV band.
  • Focal / reflector efficiency: 1.0 at design distance with clean reflectors; 0.6–0.8 typical at 1–2 inches off, with dirty or aged reflectors.
  • Lamp aging derate: % of original output remaining; a lamp at end-of-life sits around 70–80%.

How to use the result

  • Use it during early UV-station design, vendor lamp evaluation, or to ballpark whether a measured radiometer number is plausible vs the spec sheet.
  • Estimate only. Real focal/reflector behavior is not linear with distance, and the aging derate is a single number that hides accelerated decay near end-of-life. Always validate the operating spec with a calibrated radiometer pass at the actual part surface.

Common questions

  • How accurate is this estimate? Within ±20% if you have an honest focal/reflector efficiency number for your geometry. The biggest source of error is the efficiency factor — most engineers leave it at 1.0, which assumes design focal distance and a brand-new reflector. Drop it to 0.7–0.8 if the lamp is mounted off-design or the reflector has any visible discoloration.
  • Where do I find rated peak irradiance? On the lamp data sheet, usually quoted at the design focal distance and one specific UV band (UVA/UVB/UVC/UVV). Make sure the band on the spec sheet matches the band your chemistry needs — UVA mW/cm² is not interchangeable with UVC mW/cm².
  • What does aging derate look like over a lamp's life? Roughly linear for the first 70–80% of rated life, then accelerating. A lamp at 50% of rated life is typically at 90–93% of new output; at 100% of rated life it's at 70–80%; past rated life it can drop several percent per 100 hours. Track this with weekly UV Dose Margin checks.
  • Why is my radiometer reading lower than this estimate? Common causes in order: dirty quartz, focal distance off, wrong UV band on the radiometer, the radiometer is at the part surface but the part is below the design plane, or the reflector has degraded. Clean and recheck before assuming the lamp is bad.

Last reviewed 2026-05-12.