Images from cameras are usually provided in a non-linear form, often specific to a given camera manufacturer. However, tools are typically provided to convert to alternate useful forms that are independent of camera type. Of special usefulness is linear light. A linear light representation is implicitly proportional to the light seen by the camera. Exposure then becomes a multiplicative scale factor. Within the limits of the maximum exposure and noise floor, the image is inherently invariant with respect to exposure. This paper describes simple methods to verify this exposure invariance, thus providing a characterization of the useful working exposure range. The processing steps taken in making the linear representation are also implicitly verified.