UV Curing calculator

UV Heat Load Calculator

Mercury UV lamps emit a lot of IR alongside the useful UV — typically 50–70% of input power becomes heat. On flexible film, electronics, or any low-Tg substrate that heat causes distortion or substrate damage. This calculator estimates the BTU/hr hitting the part so you can size a chiller plate, a cool block, or an air knife correctly. (LED arrays produce far less radiated heat — different model.)

What this calculator does

  • Estimate the IR / convective heat load a mercury UV lamp dumps on a heat-sensitive substrate during cure — the number that drives chiller plates, cool blocks, and substrate distortion risk.
  • Use it during process design when the substrate is heat-sensitive (thin film, electronics, low-Tg polymer) and the cure cell needs cooling fixtures sized correctly.
  • Returns the heat (BTU/hr and kW) hitting the part from a UV cure exposure, used to size cooling fixtures or evaluate substrate distortion risk.

Formula used

  • Estimated heat to part (kW) = lamp electrical input × IR fraction × exposure time fraction
  • Hourly load (BTU/hr) = estimated heat × 3,412

Inputs explained

  • Lamp electrical input: Mercury arc input power; LED arrays usually need a different heat model.
  • IR fraction reaching part: 0.40–0.65 for mercury arc; lower with cold mirrors or dichroic reflectors that strip IR.
  • Exposure time per hour: Fraction of the hour the lamp is on the part; 1.0 = continuous cure, 0.3 = 30% duty.

How to use the result

  • Use it in process design for heat-sensitive substrates, when sizing chiller plates / cool blocks / air knives, and when troubleshooting substrate distortion that traces to the cure station.
  • Order-of-magnitude only. Real heat transfer to the substrate depends on substrate emissivity, focal distance, reflector type (cold mirror dramatically reduces IR), and air movement. For tight thermal designs, validate with a thermocouple on the substrate at production speed.

Common questions

  • Why is mercury so much hotter than LED? Mercury arcs radiate broadband — most of the input power becomes IR and visible light, with only ~25–30% in the useful UV band. LED arrays put 25–35% into UV at a single peak wavelength and waste much less as IR — they get hot at the array body but radiate far less heat onto the substrate.
  • How do I cut heat load without losing UV? Three real options: dichroic / cold mirror reflectors (strip IR, keep UV — drops IR fraction to ~0.15–0.25), shorter dwell at higher belt speed (less total IR exposure), or switch to LED (much lower IR by design). Active cooling (chiller plates, cool blocks under the substrate) is the fallback.
  • What substrate temperature is dangerous? Depends on the material — PET films distort around 70–80°C, PVC sooner, polycarbonate around 130°C. For electronics, anything that exceeds the assembly's reflow / re-flow risk temperature is a problem. Always check substrate Tg / max-service temperature against measured surface temp at production speed.
  • Does this calc work for LED systems? It's not the right model. LED radiated IR is much lower; most heat shows up at the array body and gets removed by the array's water or air cooling system, not at the part. For LED retrofit thermal sizing, measure substrate surface temperature at production setpoint instead of using this calc.

Last reviewed 2026-05-12.