I would first suggest checking out the example available on our Libstock page:https://libstock.mikroe.com/projects/view/1593/lux-meter-with-bh1750
It will be a good starting point for you.
Also, I would suggest reading the datasheet for the sensor:http://www.mouser.com/ds/2/348/bh1750fvi-e-186247.pdf
As for your dilemma, you can try to add a piece of code which has some kind of IF condition.
For example, if the sensor senses ambient light data and returns a value of let's say 10 lux, then you write a piece of code which states what to do.
Another condition would be let's say, if the luminescence is 20 lux then do something else.
The sensor itself is I2C based.
I hope this helps out.