Hi,
I notice light is used as a countable noun in this context. What is 'a light', a flash of light? It more often refers to a source of light. eg a lamp, a flashlight, a candle, a torch.
Also, what's the meaning of "light up every corner of the heart"? It doesn't mean that someone cuts open the heart with a knife and sticks in a flashlight. 
Instead, it's poetry. Light is often seen as a sourceof happiness, warmth, understanding, etc. And darkness is often seen in the opposite way. Is that not also true in your culture?
Best wishes, Clive