It is important to test with appropriate lighting levels. This is both to ensure autofocus operation is accurate and representative of what the camera and lens is capable of, and to reduce the risk of vibration caused by shutter operation.
You will be told if the lighting level is not ideal, with suggestions on what to correct.
FoCal is measuring and/or calibrating the best possible performance of the camera so it’s important to ensure that your target is well lit with good, stable lighting. We don’t recommend using LED or fluorescent lights unless you can guarantee that they do not flicker in a way which can cause problems for either the camera or FoCal’s analysis.