Doomed.io has a day and night cycle that will change level of avialble light over a period of time. When night starts to decend you may no longer see trees, rocks and other resources, the only visibility will be in a small light circle that sourrounds your character only visible to you and not other players. Additionally creatures will no longer be visible until they are close enought to enter your light circle.
It is unconfirmed but it seems like wild animals like bears and wolfs will spawn more frequently during the night cycle. LIkely to encourage players to have built a base they can retreat to when it gets dark.
Torches of varying degrees can be used to light up an area during night time, but will light that area up for all players not just the one that set them.
Tip: Wolves are much faster now in 1.1, so always keep a sword out during night in case a wolf sneaks up on you. I really don't believe day-night affects how frequent wolves and bears spawn, but they attack a lot faster.