Today I received two TSL235 sensors that convert incoming light to frequency. As there was no article on the playground yet on this particular sensor I wrote a small sketch and added some comments - http://arduino.cc/playground/Main/TSL235R - to get people started. The code does not compensate for anything yet (input voltage, temperature etc) ; maybe some future version.
In contrast to the TSL230R it has no configurable divider for the frequency so the # IRQ's can become quite high. Today's max inhouse ~160000 . Therefor I used only the rising edge for the IRQ routine. When it is really really dark one could use CHANGE edge for the IRQ, to double the precision, but be carefull as your Arduino might get stalled during daylight :)
As always comments and remarks are welcome,