What is Cut-on Wavelength? (Longpass Filter)

Longpass filter:

• Cut-on wavelength: This represents the shortest wavelength that the filter transmits efficiently. Below this wavelength, the filter rapidly blocks light with increasing effectiveness. Defined as the wavelength where the transmission rises to 50% of its peak value.

• Longpass filters "pass long wavelengths" and block shorter ones. Therefore, the cut-on wavelength defines the lower limit of the transmitted wavelengths.