Where do you get 7V from? Best is to ditch the LDR and use a photo transistor and feed it from the same VCC as you drive your processor with. Then you know that the voltage swing is between 0V and 5V (or maybe 0V and 3.3V). You might get away with connecting that signal directly to the processor, or possibly add a comparator or a buffer with schmitt-trigger input, i.e. with hysterese between the high-to-low and low-to-high transition levels.