It's been a long time I've worked with CDS cells as such, but AFAIR there was no mention of light flashing the cell for low light reading.
The CDS cell's resistence increases as light decreases (that's why less current flows through them) and, for low light levels this resistence increase is a quite slow process indeed. That's one of the reasons they were replaced by other technologies.
So, it doesn't makes sense to me to flash it with light - any reading in this condition could be false.
Do a test: in a dark place, read patiently the light of an even surface until it stablizes. Then flash it and read again after stabilization.
If the flashed reading indicates more light, I woul feel this is a fake reading.