I own a Logitech C920 Pro and a software called webcam settings allows me to easily turn off the lights. If this software can do this, so can a malware.

Also, a malware can be designed to click quick snaps when there is no keyword or mouse activity for a specific period. This can help the malware go unnoticed without controlling the light. Want to take it to the next level? You can use the mic anytime to estimate the user's distance from the system and then enable webcam accordingly. I know this would not be very accurate, but possible.