Colored glass filters are made of colored glasses that transmit certain range of wavelength light and absorb the rest. There are several major types of colored glass filters:
Longpass filters (GFL-xxx)
These filters are characterized by their ability to transmit over a wide spectral range with transmission being “cut-off” below a specific wavelength. They exhibit high transmission over the wavelength region above the “cut-off” wavelength and have full absorption in the wavelength region below the “cut-off” wavelength. They are useful for sorting applications, food and beverage inspection, imaging systems, machine vision, and sensing applications.
Bandpass filters (GFB-xxx)
These filters are used to isolate specific regions of a spectrum. They transmit light within defined wavelength ranges while absorbing other undesired wavelengths. UV bandpass filters are often used to selectively transmit desired UV illumination such as 254nm and 365nm mercury lines, IR bandpass filters are often used in night vision and IR sensing systems, whereas visible bandpass filters can deliver desired wavelength range in color applications.
Heat absorbing filters (GFB-x9x)
Strictly speaking, these filters are also part of Bandpass filters. Since they are transparent in the visible range but opaque in the infrared range, they can be used to absorb infrared radiation. They’re useful in applications where unwanted heat can increase discomfort or cause damage.
Neutral density filters (GFN-xxx)
These filters evenly absorb light across the visible spectrum. They’re used to reduce transmittance of light in industrial and imaging applications. Lasers or other high intensity light sources can also cause damage to sensitive sensors and they may need to be attenuated with a neutral density filter. Neutral density filters are also used to test the photometric accuracy of instruments such as spectrometers.