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Type and Definitions of Filters

From Edmund Optics Inc.
 

 

Bandwidth: The wavelength range that a filter passes. This width is defined at a specific transmission value. In the case of interference filters, the standard is to define bandwidth as Full Width at Half Maximum (FWHM) or the entire width (in nm) that has a transmission higher than half the transmission of the peak wavelength.

Central Wavelength: Typically used to denote the peak transmitting wavelength of a filter. It is, however, actually the midpoint determined by the passband wavelengths where the transmittance is 50% of the peak (called the half bandwidth or FWHM). For interference filters, the peak is typically not at the midpoint wavelength.

Optical Density: The optical density (OD) is related to the amount of energy transmitted through a filter. Higher OD indicates lower transmission. Transmission can be calculated using the following equation: T = 10-OD * 100 = % transmission

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