Help Interpreting "Max light exposure" rating for TSL1406R
I think it's intended to be for pulsed laser conditions. Probably for pulse times short in comparison to the thermal time constant (which will be more than microseconds but much less than 1 second).  

I would expect that relatively high energy pulses in excess of the maximum would permanently damage the chip in some way, maybe overvoltage failure of the capacitors or something else 'bad'.