Are Lions Actually Nocturnal?

Lions are predominantly nocturnal, in fact they are crepuscular.  In otehr words, they spend most of their lives asleep, often sleeping up to 20 hours a day !
This helps them conserve energy as well as avoid the very high temperatures during the day.   Prey is usually few and far between for them, so there is little point in spending too much time awake.
Lions usually sleep together in a  group and often rub their heads together.  This helps to strengthen social bonds between the lions.
In the short times they are awake, they will hunt.  They usually hunt as a group and will spread out and surround their prey rather like a ring around it, so it cannot escape.  
However, they usually find some time in the day for play and will 'play fight' each other and spend a little time just being like 'big cats' which in reality they are !