How Much can be knocked down to let the light in ?

I don't understand why you think the landlord has any control over your neighbor's house. Do you really expect that he can insist that the neighbors chop off the top of their house do that it doesn't block the sun from shining on the house that you rent?

Direct sunlight was not a stipulation in your lease/mortgage or other contract so it's a privilege that is not a right.Ummmm I'm suing God because he put clouds in front of my Sunlight. Christian Bale loves lights too.

Contrary to what many people think you have no right to light.  You think your landlord can knock down the house next door?

Bummer. Can't do anything about the neighbor's house.

How much of what The next door house? None of it.

Are you asking if he can knock down the house next door? WADA!

Take your meds & if you are not on any then seek psychiatric help. 

They are not going to be taking down any part of the building & if you honestly think they would then you need to be in an institution. 

You only option is to move. No? You will have to go without light then.