This paper, submitted to IEEE Transactions on Geoscience and Remote Sensing, discusses ways to quantify the light collection by a camera, which is critical for the signal to noise ratio of the imagery. Based on a generalized analysis of a camera from an outside “black box” perspective, a preferred metric for light collection is identified, denoted A*. It is argued that this quantity can serve as a comparative figure of merit for cameras, as well as an element of image metadata. The work addresses conventional cameras as well as hyperspectral cameras. The proposed metric is part of the draft standard for hyperspectral imaging being developed by IEEE SA P4001.