ANSI C78.377:2017 pdf free download – American National Standard for Electric Lamps- Specifications for the Chromaticity of Solid-State Lighting Products
4.1 Basis
The chromaticity coordinates and correlated color temperature (CCT) values used in this standard are based on the CIE colorimetry system. While the chromaticity of light is expressed by chromaticity coordinates such as (x, y) and (u’, v’) the chromaticity of nominally white light can also be expressed by CCT and the distance from the Planckian locus. CCT is a more intuitive measure of the shade of white light than (x, y) or (u’, v’). Since CCT is defined based on the (u’, 2/3v’) chromaticity diagram, the distance from the Planckian locus should be determined on the same diagram. It should be expressed as a signed value to indicate whether the chromaticity is above or below the Planckian locus. As such a distance parameter with respect to the Planckian locus is not officially defined by the CIE, “Duv” (symbol: D uv ) is defined in this document as the closest distance from the Planckian locus on the (u’, 2/3v’) diagram, with “+” sign for above and “−” sign for below the Planckian locus.
4.2 Nominal CCT and Target CCT
Nominal CCT is used to specify and communicate chromaticity information of a product, and, in this document, is a CCT value at 1 00 K steps that is closest to the target CCT of the product. A target CCT is the CCT value that the product is designed to produce. Individual samples of the product may deviate from the target CCT due to production variation, which is normally controlled to be within a production tolerance. The same applies to target Duv. The target CCT and target Duv are also the center points of the tolerance range of these parameters in this document.
4.3 Specifications
SSL products included in this standard shall have chromaticity values that fall into one of the nominal CCT categories listed in Table 1 or Table 2. SSL products with a given nominal CCT shall have the defined target CCT and Duv, and the values of individual samples shall be within the tolerances of CCT and Duv as listed in Table 1 or Table 2. Measurement of chromaticity shall be made in accordance with methods.
4.3.2 Extended Specification
SSL products included in this Extended Specification shall have chromaticity values that fall into one of the additional CCT categories listed in Table 2. SSL products in these categories shall have CCT and Duv values of individual samples falling within the tolerances of CCT and Duv as listed in Table 2. Measurement of spectral power distribution and calculation of chromaticity shall be made in accordance with methods given in the normative references. Extended Flexible CCT specification allows the use of a CCT other than those listed under nominal CCT category. The Extended Flexible CCT/Duv specification allows the use of a center Duv value different from those listed in the first ten CCTs of Table 2.