Also referred to as waveband, passband, or bandwidth, bandpass is the wavelength range used to denote a specific part of the spectrum that passes incident energy through a filter. The first order is always at the design wavelength of the filter.

  See also Notch Filter , Filter , Full Width at Half Maximum (FWHM) , Cavity , Central Wavelength (CWL)

The blocking amount is the amount of light that is rejected, not passed, by a filter outside the passband. It is expressed as the ratio of total energy transmitted outside the passband to the total energy transmitted within the passband. Blocking values are given over a specified wavelength range.

  See also Cavity , Blocking Range , Optical Density (OD)

Also referred to as the stopband, blocking range is a wavelength range used to specify a spectral region of energy that is not transmitted by a filter. It is typically specified in terms of Optical Density (OD).

Used to denote the peak transmitting wavelength of a filter, it is the midpoint determined by the passband wavelengths where the transmittance is 50% of the peak (denoted by the Full-Width at Half Maximum).

  See also Filter , Bandwidth

Cut-off wavelength is the wavelength at which transmission decreases to 50% in a shortpass filter.

  See also Filter , Cut-On Wavelength

In filter terminology, cut-on is the wavelength at which the transmission increases to 50% throughput in a longpass filter.

  See also Cut-Off Wavelength

Filters are optical components that transmit, reflect, or absorb certain wavelengths or frequencies of light. Filter types include bandpass, longpass, shortpass, interference notch and rugate notch, color, dichroic, and neutral density.

  See also Cold Mirror , Cavity , Central Wavelength (CWL) , Stopband , Longpass Filter , Neutral Density Filter (ND) , Rugate Notch Filter , Heat Absorbing Glass , Notch Filter , Peak Transmittance , Shortpass Filter , Full Width at Half Maximum (FWHM) , Bandwidth , Fluorescent Filter , Hot Mirror , Dichroic Filter , Cut-Off Wavelength , WRATTEN Filter , Cut-On Wavelength , Interference Filter , Dichroic Coating

A specific wavelength region of the bandwidth of a filter defined by the two points of the passband where transmittance is 50% of the peak.

  See also Filter , Bandwidth , Central Wavelength (CWL)

A type of filter in which the transmission band is a region of longer wavelengths as compared to the region blocked.

  See also Shortpass Filter

A type of filter that yields a constant value for attenuation, or optical density, over a bandwidth (i.e. spectrally flat). It is useful for attenuating, or reducing, overall light in a system.

A type of filter designed to block a pre-selected bandwidth and transmitt all other wavelengths within the design range of the filter. Notch filters are manufactured using the dielectric stack method which involves using a series of thin layers of dielectric materials, of alternating refractive index.

Optical density is a value that describes the amount of energy that can pass through an optical material. It is directly related to the transmittance of the material. The greater the OD, the more light being blocked.

  See also Continuously Variable Apodizing Filter , Blocking , Neutral Density Filter (ND)

The highest transmittance value for light being passed by a filter.

  See also Filter

The wavelength of light that has the highest transmittance value.

Radiation that changes direction, but not wavelength, after contact with a material surface.

  See also Transmission , Parity

A type of filter where the transmission band is a wavelength range of shorter wavelengths, typically lower than the region blocked.

  See also Filter , Longpass Filter

The amount of radiant energy that passes through an optical medium, not being absorbed, reflected, or scattered.

  See also Reflection

The peak to peak distance covered by one cycle of an electromagnetic wave. It is inversely related to frequency. The longer the wavelength, the lower the frequency; conversely, the shorter the wavelength, the higher the frequency.