遮光 is mostly used as a modifier in product compounds:
遮光窗帘 (blackout curtains),
遮光罩 (lens hood / light shield),
遮光板 (sun visor in a car),
遮光率 (light-blocking rate). Verbal use ('block out the light') exists but is much rarer in everyday speech than
挡光 (dǎngguāng).