spectral transmittance

[7.5.3.14] τ(λ)=φ_τλ/φ_iλ

The ratio of the transmitted flux to the incident flux at a particular wavelength, λ, or within a small band of wavelengths, Δλ, about Δ.

Note: The various geometrical aspects of transmittance may each be considered restricted to a specific region of the spectrum and may be so designated by the addition of the adjective “spectral.”