ok cover the inside of the walls with a reflective cover here are your top choices

1) Mylar- very reflective with light
2) white paint- same as mylar
3) aluminum foil(shiny side)- this will work also

you should have considered doing this either way b/c once you line the walls with a reflective cover then your light will be used to the max and will cover those light spots, i have the same kind of cabinet too only mines bigger that i got from home depot if u want i can show u pics of mine.