"光监测装置" can be translated into English as "light monitoring device" or "optical monitoring apparatus".
"Light monitoring device" is a more straightforward and commonly used term, directly conveying the idea of a device for monitoring light.
"Optical monitoring apparatus" is a more technical and precise term, with "optical" emphasizing the optical or light-related nature of the monitoring, and "apparatus" referring to a set of instruments or equipment used for a specific purpose.
Both translations are acceptable, and the choice between them may depend on the specific context and the level of technicality required.