The BPI^® RGB Spectrometer uses a special detector chip with four separate sensors for red, green, blue, and white (unfiltered) light. In addition, an infrared-absorbing filter is placed over the sensor to prevent it from seeing any wavelengths which would be invisible to the human eye. The light source is a pair of light-emitting diodes: one LED is white with a blue exciter, and the other is violet, thus providing coverage of the whole visible spectrum. The device is calibrated at the factory with colored filters of known characteristics so that the internal microcomputer can perform the linear transformation of the RGB space defined by the sensor and the light source into the standard XYZ space. The XYZ coordinates are then further transformed nonlinearly into the CIE LAB space.

External to the meter, a Windows™ PC reads the same numbers that are displayed on the front panel via an RS-232 serial connection. (For computers that are not provided with RS-232 ports, there are inexpensive USB devices which will add serial ports without requiring the computer to be opened.) The computer can then save standard colors to a database, compare one color with another, and suggest correction tints to make one dyed lens better match another.

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