(under subclass 409) Subject matter including a filter element in the visible range positioned in the light transmission path of visual and photosensitive testing apparatus.
(1) Note. Included in the group are visual extinction type, sequential and simultaneous comparison tests involving at least one known color standard and one unknown liquid. The standard may be a colored light source or light source plus a colored light transmissive filter.
(2) Note. An infrared filter for the purpose of transmitting infrared or for preventing the heat rays of a light source from entering the liquid tested is not a filter under the definition of this subclass.
SEE OR SEARCH THIS CLASS, SUBCLASS:
51, for liquid colorimeters which include an infrared filter in the test or for the purpose of removing heat radiation from affecting the test results. See (2) Note above.
416+, for color-transmitting filters used in measuring shade or color, per se.
432+, for light transmission tests where no color or concentration of a solute in a solvent is involved in the optical test.
SEE OR SEARCH CLASS 250, Radiant Energy,
211, for circuitry having photocells with inherent color sensitivity; subclass 226 for optical or prephotocell systems which include filters within the visible spectrum.
359, Optics: Systems (Including Communication) and Elements,
577+, for interference type filters; and subclasses 885+ for filters generally which may be used to produce monochromatic bands of radiation within the visible spectrum.
