Filters and Optical Coatings: The Wavelength Selector of IPL Systems

IPL’s broadband light passes a cut-off filter: a “560 nm” filter transmits above 560 and reflects below. The number is only the cut point — spectral shape and purity come from the coating stack, where the thickness precision of dozens of dielectric layers sets edge steepness and out-of-band suppression.

• Cutoff steepness: cheap stacks slide gradually, leaking short wavelengths that add epidermal heat load (more pain, more PIH).
• Coating life: films absorb and degrade under high fluence — filters are the hidden consumable of IPL, their life tied to shots, fluence and cooling.
• Coating uniformity: cut-point drift from center to edge of large apertures produces side-to-side efficacy differences.

1. Ask for the spectral transmission curve, not just the number.
2. Ask for coating-life commitments and replacement criteria.
3. An aging IPL with stable fluence but rising pain — put filter degradation on the troubleshooting list.

Can filters be washed?

Coatings fear scratches and chemicals; clean per the vendor’s method (usually lint-free cloth plus specified solvent) — improper cleaning is a classic cause of early aging.

Multiple filters in one handpiece vs multiple handpieces?

Engineering-equivalent; multi-handpiece designs make swaps and filter-life management easier. The difference is cost structure and workflow habit.

• IPL
• DPL
• Handpieces