Answer to Question 1
The two sources are: (1) natural light from windows and (2) artificial light from lamps.
Answer to Question 2
If an animal is kept in an environment where it is uncomfortable, it will experience stress, which can negatively affect its health and growth. If an animal becomes sick, it will require medical treatment and, potentially, quarantine, both of which can be expensive. Additionally, the smaller and less healthy the animal is, the less valuable it will be at market.