The cameras in Apple's next AirPods are not there to take photos. Infrared sensors sit in both the left and the right earbud and capture the world in low resolution, and what they see goes to Siri so it can answer questions about whatever is in front of you.
The thing to picture is Face ID, not a phone camera. Apple is expected to use tiny infrared cameras of the same kind Face ID already uses, which is why the stems grow slightly to house them.
An LED lights when the data leaves the earbuds. According to Bloomberg, the light comes on while visual information is being sent to the cloud for processing, so the trigger is the network connection rather than the sensor being awake.
Ming-Chi Kuo has said the cameras would detect changes in your surroundings and possibly allow in-air gesture control.
None of it is settled. A leaker described the project as suspended in early July, and Apple could hold the earbuds back if it is not satisfied with the Visual Intelligence work in Siri. By early August the target had moved again, to a launch as soon as this year.
The resolution is low and the light is the part you notice.