Most often I recommend complete darkness. However, sometimes the the developing child needs to see where they are moving in the night. Gross motor development can be very disruptive to sleep.
Everything this toddler is doing in the day, he is also doing in his crib at night. The crib is a busy place. The brain is revisiting all they are learning and quite often the body follows. This can all take place in sleep, in light sleep, and prompt your child to become fully awake and cry out.
Light can help. However, we want it to be as dim as possible and amber in color. Blue light and LED light can affect melatonin production.
Here are a couple of solutions
This bulb is the right color and on a dimmer switch is less bright. You may want to put it on a timer so that it comes on later in the night or early morning.