UV Curing calculator

UV Intensity Decay Calculator

UV lamp output drops every hour they run. The honest way to manage that is to track today's irradiance against the day-one baseline and act when it crosses a documented threshold. This calculator does that conversion in one step: today's reading ÷ original baseline = % of new, with a verdict against your minimum-acceptable percent. Drop it into a process control log and the trend tells you when the lamp is done long before quality does.

What this calculator does

  • Calculate how much UV irradiance has dropped vs a brand-new lamp baseline, with a verdict against your minimum-acceptable percent.
  • Use it after every radiometer pass to trend lamp aging objectively and decide whether to swap, slow the line, or keep going.
  • Returns today's UV irradiance as a % of the original new-lamp baseline, plus the headroom over your documented replacement threshold.

Formula used

  • % of new = today's reading ÷ original baseline × 100
  • Headroom = % of new − replacement threshold

Inputs explained

  • Today's irradiance reading: From a calibrated radiometer pass at the same position used for the baseline.
  • Original (new lamp) baseline: Reading from the day the lamp was first commissioned, same position and radiometer.
  • Replacement threshold: Trigger to plan a swap; mercury 70–80%, LED 75–85% of new.

How to use the result

  • Use after every scheduled radiometer pass, after a deep clean, and any time you suspect the lamp / driver / reflector has aged faster than the maintenance plan assumes.
  • Decay is rarely linear — it accelerates near end-of-life on mercury lamps and after the L70 point on LEDs. A reading just above threshold this week may dip below within 50–100 hours. Act on the trend (slope of the last 4–6 readings), not just today's number.

Common questions

  • What's a normal decay curve for mercury vs LED? Mercury: roughly linear loss of ~5–8% per 1,000 hours through 70% of rated life, then accelerating. LED: very slow loss for the first 10,000–20,000 hours (often <10% over that span), then a steeper drop past the L70 point quoted on the array spec sheet.
  • Where do I get the original baseline? Take it on day one of every new lamp install — a profiling pass with the production radiometer, position logged in the maintenance record. If you never recorded it, use the lamp's data-sheet rated irradiance as a fallback, but flag the result as estimated until your next lamp swap establishes a real baseline.
  • What replacement threshold should I set? Most spec sheets call out an 'end-of-useful-life' threshold of 70–80% of new for mercury and 75–85% for LED L70. Pull from the data sheet for the actual lamp; default conservatively if unspecified. Pair the threshold with a UV Dose Margin check — if the chemistry is dose-tolerant you can run lower, and vice versa.
  • Today's reading is higher than baseline — what's going on? Almost always a measurement issue: cleaner quartz than baseline, different focal distance, different radiometer, or wrong UV band. Mercury arc lamps don't recover output. Verify the reading procedure, then re-baseline if the change is real (e.g. you replaced the reflector).

Last reviewed 2026-05-12.