If you want to compensate for ambient light, you are making an oscillator. Because the ambient light is also the light of the nearby lamp.
Take a look at the ABC guide, http://www.pighixxx.com/abc-arduino-basic-connections/
For example the mosfet on the bottom-left of "Card 3". Click on "Set 1 (Card 1,2,3)" to open the pdf.
This is a mosfet that can switch it, N-Channel MOSFET 60V 30A - COM-10213 - SparkFun Electronics
Never mind that it is able to switch 30A. A mosfet of 30A is perfect to switch 1.6A.
There are so many light sensors.
You could connect an LDR and a resistor to an Arduino analog input (ABC guide, card 1, lower-right), 20 for 2 dollars on Ebay.
Or photodiode, 2 dollars on Ebay.
Or an expensive lux sensor.
For programming, start with the examples that come with the Arduino IDE.
How do you want to detect if a person is present ?
A PIR sensor only senses motion.
Perhaps ultrasonic ? But what if someone places a tall box under a lamp ?