If there are too many trees, the light doesn't reach the house.
Literal
Tree [subject-が] too-many [when-と] house [to-に] light [subject-が] does-not-shine.
多すぎる stacks 多い ('many') with the excess suffix ~すぎる ('too much X'). The と clause gives the conditional — 'if there are too many trees, Y follows.' 射さない is the negative of 射す ('to shine, stream [of light]'). Light is the subject, with に marking its destination (the house).