Designing a wide-range light detector circuit
You can hardly think of anything simpler than a photodiode or phototransistor: place a series resistor and you have a voltage proportional to light level. The resistor's value sets the sensitivity. In the past I've used the SFH3410 for this several times.

You want a phototransistor with a eye-matched sensitivity curve. Most phototransistors are rated for a limited light range, like the SFH3410, which is only specified between 10 lux and 1000 lux. I've used it for levels down to 1 lux as well, and it was still linear at that level.  

For higher levels (direct sunlight in summer can go beyond 100 000 lux) I would suggest to use a second phototransistor where you place an ND (neutral density) filter in front of it. A 99 % filter will reduce the 100 000 lux to 1000 lux, so you can measure the higher light levels with the second phototransistor.