10 copies of UAS regulatory sequence drive expression of the Chrimson optogenetic tool. Includes a C-terminal fusion of a Drosophila codon-optimized tdTomato tag, a 'Syn21' leader, an ER export signal (FCEYENEV), a 67bp intron derived from Mhc ('IVS'), and a membrane-trafficking signal from Hsap\KCNJ2.