Is 75% of new the right replacement threshold?

Only if it matches where your process actually fails, which is measurable. The percent-of-new at process limit row shows that point; move the rule to meet it.

Why do my readings jump between checks?

Measurement conditions usually dominate. Distance matters most: a point source changes with the square of distance, so a small height difference swamps months of decay. Fix position, band, warm-up and instrument.

Does lamp output decay evenly across bands?

No. Mercury lamps age unevenly, and envelope darkening cuts the short wavelengths hardest. A broadband reading can look healthy while the band your photoinitiator absorbs has fallen further.

Can I run below the required irradiance?

Only by giving the part more time. Dose is irradiance times exposure, so slowing the line restores dose. That is a throughput trade, and some chemistries need peak irradiance rather than accumulated dose.

UV Curing calculator

UV Intensity Decay Calculator

Compare today's lamp reading with its new-lamp baseline, then check the plant's replacement rule against what the process needs. Enter both readings, the rule and the required irradiance.

What this calculator does

Track lamp output against its new-lamp baseline, and test the replacement rule against the process requirement.

Formula used

% of new = today's reading ÷ new-lamp baseline × 100
Headroom = % of new − replacement threshold
Process margin = (today's reading − required) ÷ required × 100
% of new at process limit = required ÷ baseline × 100
Reading the rule replaces at = baseline × threshold ÷ 100

Inputs explained

Today's Irradiance Reading: Current reading at the same position, band and belt height.
New-Lamp Baseline Irradiance: The reading recorded when the lamp was new.
Lamp Replacement Threshold: The percent-of-new rule the plant replaces at.
Irradiance the Process Requires: Reading below which this process stops curing at line speed.

How to use the result

Best suited to deciding whether a flagged lamp really needs changing, setting a replacement threshold from a cure trial, investigating cure failures on a rule-passing lamp.
A single-point reading misses ends falling away; the uniformity page covers that. Ignores spectral shift: a healthy broadband reading can hide a weak cure band. Cannot tell lamp decay from a dirty quartz sleeve or a drifting radiometer.

Common questions

Is 75% of new the right replacement threshold? Only if it matches where your process actually fails, which is measurable. The percent-of-new at process limit row shows that point; move the rule to meet it.
Why do my readings jump between checks? Measurement conditions usually dominate. Distance matters most: a point source changes with the square of distance, so a small height difference swamps months of decay. Fix position, band, warm-up and instrument.
Does lamp output decay evenly across bands? No. Mercury lamps age unevenly, and envelope darkening cuts the short wavelengths hardest. A broadband reading can look healthy while the band your photoinitiator absorbs has fallen further.
Can I run below the required irradiance? Only by giving the part more time. Dose is irradiance times exposure, so slowing the line restores dose. That is a throughput trade, and some chemistries need peak irradiance rather than accumulated dose.

Last reviewed 2026-10-01.