I actually think there isn't enough light for a good reading. So in my first post I did tell the OP to make some measurement inside the camera and see if he would get any reading. If the light is strong enough above EV-2 for ISO 100 which is only about 6 lux. At ISO 6 you only need about 1.7 lux for a 1 second exposure. If we were to expect exposure to be longer than 1 seconds than the meter can't measure that low a light level. Enlarging meter I think is in order or may a color analyzer in the white channel.
Originally Posted by BrianShaw