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Performance metrics & physics

Wavelength

Wavelength is the distance between successive peaks of an electromagnetic wave; the solar spectrum runs from ~300 nm UV through 380–780 nm visible to multiple-thousand-nanometre infrared.

Wavelength determines how electromagnetic radiation interacts with matter. UV at 300 nm has enough energy to break chemical bonds (sunburn, fading). Visible light at 500 nm carries the colours we see. NIR at 1500 nm carries solar heat.

Window film spectral curves plot rejection vs. wavelength. A good film is selective — high rejection in UV and NIR, moderate transmission in visible.

For technical comparisons between films, ask for spectral curves rather than single-number summaries. A film with high "average IR rejection" but a notch in a key band may underperform in real conditions.