Color Temperature Orange (alternatively, Correct to Orange). A range of color correction filters used to lower a source's color temperature. Available from all four major gel manufacturers and also available in dichroic filters. Full CTO will convert 5500K to 2900K 1/2 CTO will convert 5500K to 3800K 1/4 CTO will convert 5500K to 4500K 1/8 CTO will convert 5500K to 4900K Some also offer 1/3, 2/3, and 3/4 varieties. For more, see the links and attachments to the wiki entry color temperature . Note that not all manufacturers' products are exactly equivalent.