If you take a red led and stick the -/ground leg in Arduino GND and the + leg in Arduino A0 then read and print the ADC at wide enough intervals, it will build up to 1.5V in bright light. If you read it more often it returns less, the current from light striking the led is low enough that continuous ADC reads can flatten it.
It leaves me thinking that if I use a 3.3 Vref (instead of 5V) and seek what read frequency maintains readings of 100 or even 50 that it might be half-fast...... (runs off lol-ing)