Optical Filters 2013 - SCHOTT North America

18Chromaticity coordinates relevant to Night Vision Imaging Systems (NVIS) compatibilityare described in terms of the UCS coordinates u' and v'. These coordinatesare directly related to the CIE 1 x and y coordinates by way of the followingformula:12u' =4x9yand v' =–2x + 12y + 3 –2x + 12y + 3where:u', v' = 1976 UCS chromaticity coordinates according to CIEx, y = 1931 chromaticity coordinates according to CIEAdditionally, the UCS chromaticity coordinates can also be expressed in terms ofthe tristimulus values X, Y and Z:13u' =4XX + 15Y + 3Z9Yand v' =X + 15Y + 3ZFor illumination systems to be designated as NVIS Green A, NVIS Green B, NVISYellow, NVIS Red, or NVIS White compatible, the chromaticity of the illuminationsystem must adhere to the following formula:14(u'– u' 0 ) 2 + (v'– v' 0 ) 2 ≤ r 2where:u' 0 and v' 0 = 1976 UCS chromaticity coordinates of the center point of the specifiedcolor areau' and v' = 1976 UCS chromaticity coordinates of the color locus of the illuminationsystem (e.g. combination of filter and light source)r = radius of the permissible circular area on the 1976 UCS chromaticitydiagram for the specified color3.10 Brightness / photopictransmittanceThe tristimulus value Y (Brightness) may be replaced by the expression “PhotopicTransmittance.” The relation between Y and Photopic Transmittance is simply afactor of 100 %.Example: Brightness Y = 57 corresponds to Photopic Transmittance = 57 %1 Commission Internationale de l’Eclairage, Vienna, Austria. http://www.cie.co.at/