Why the wavelength matters
Infrared heaters transfer energy by radiation. A material only warms up from the radiation it absorbs; whatever it reflects or lets pass through is lost to the process. How much a material absorbs depends strongly on the wavelength, so the same heater can be very efficient on one product and wasteful on another.
Matching the emitter to the material gives faster heating, more even temperatures and lower energy use. A mismatch shows up as long heating times, hot machine parts, or surfaces that overheat while the core stays cold.
Emitter temperature sets the wavelength
Every infrared emitter radiates a broad spectrum, but its peak moves to shorter wavelengths as the emitter gets hotter. Wien’s displacement law gives the peak directly from the emitter temperature:
| Emitter type | Typical emitter temperature | Peak wavelength | Time to full power | Power density |
|---|---|---|---|---|
| Shortwave quartz (IR-A) | about 2,200 °C | about 1.2 µm | about 1 second | Very high |
| Carbon / fast medium wave | about 1,200 °C | about 2.0 µm | 1–2 seconds | High |
| Medium wave quartz (IR-B) | about 900 °C | about 2.5 µm | about 1–2 minutes | Medium to high |
| Ceramic (IR-C) | about 300–750 °C | about 2.8–5 µm | several minutes | Low to medium |
Typical values; exact figures depend on the emitter model and how hard it is driven.
How common materials absorb infrared
Materials have absorption bands, wavelength ranges where they take up radiation strongly. The table summarises the behaviour of materials that are heated most often in industry.
| Material | Absorption behaviour | Usually best emitter |
|---|---|---|
| Water, water-based paints, inks and adhesives | Very strong bands near 3 µm and 6 µm | Medium wave, carbon or ceramic |
| Most plastics (PP, PE, PS, ABS, PMMA, PVC) | Strong absorption above about 3 µm; shorter wavelengths penetrate deeper | Ceramic or medium wave for sheet; shortwave for through-heating, e.g. PET preforms |
| Glass | Largely transparent below about 2.5 µm, strongly absorbing above about 4 µm | Ceramic or medium wave to heat the glass itself |
| Metals | Reflect most infrared; absorb more at short wavelengths and when oxidised, painted or dark | Shortwave with high power density |
| Paints, powder coatings, organic layers | Broad absorption; dark pigments absorb shortwave well | Shortwave on metal parts; medium wave for water-based layers |
| Wet textiles, paper and board | Dominated by the water they contain | Medium wave or ceramic |
Surface heating or through-heating?
Long-wave radiation is absorbed within the first fraction of a millimetre of most non-metals, so it heats the surface. Shorter wavelengths penetrate deeper into many plastics and coatings before they are absorbed. That is why shortwave lamps are used to heat PET preforms evenly through the wall, while ceramic heaters are preferred when only the surface or a thin sheet should be heated gently.
Response time and control
Shortwave and carbon emitters reach full output within seconds and cool down just as fast. They suit processes that start and stop, conveyors that may halt, and zone-by-zone control. Medium wave and especially ceramic emitters store heat; they are slower to control but give very steady radiation in continuous processes and are robust in demanding environments.
Checklist for choosing the emitter type
If two emitter types fit, a trial with a sample of your material is the quickest way to decide. Many lines combine types, for example shortwave to gel a powder coating quickly and medium wave to finish the cure.
- What has to absorb the energy: water, a coating, a plastic, glass or a metal part?
- Should the material heat through its thickness or only at the surface?
- Does the process run continuously, or does it start and stop?
- How much space is available? Higher power density means more power per square metre.
- Is the product heat-sensitive? Longer wavelengths heat more gently.
- Are there existing heaters and controllers whose settings should stay valid?
Related products
Frequently asked questions
What is the difference between shortwave and medium wave infrared?
Shortwave emitters run at about 2,200 °C with a peak near 1.2 µm, reach full power in about a second and deliver very high power density. Medium wave emitters run at about 900 °C with a peak near 2.5 µm, take a minute or two to reach full power and are absorbed better by water and many plastics.
Which infrared wavelength is best for plastics?
For most plastic sheet, ceramic or medium wave emitters, because plastics absorb strongly above about 3 µm. For PET preforms, shortwave lamps are used because they heat through the wall thickness.
Which infrared heater is best for drying water-based coatings?
Medium wave and carbon emitters, because water absorbs very strongly near 3 µm, close to their peak wavelength.
Why do metals need shortwave infrared?
Bare metals reflect most infrared radiation. They absorb a larger share at short wavelengths, and shortwave emitters also provide the high power density needed to heat metal parts quickly.
