Im struggling with this problem, specially with the transistor.
Problem ask for:
R2 for max light on LED at night
R1 for correct working
Can LED work at day light?


My problem is: For R2 i assumed T1 on saturation, then i design R2 for 10mA, so i got 920 ohms. Im stuck at this point, dont know how to use/prove saturation or active T1.

 

Rule of thumb for sat is Ibase = Icollector/10. This is also referred to as
forced beta.

Example curve from a transistor -



Regards, Dana.