Having this item makes Isaac and his tears glow green, with the tears themselves also taking on a green hue.
All shots with this item leave a small puddle of friendly green creep, which damage enemies that walk over it, though these puddles are usually too small and disappear too quickly to be effective.
Although it looks like the tears glow, they don't produce light.
PC ABP0 1DJA item room near start
PS4 V8ZG HD31 1st item room
Vita 2J39 EANS item room near start