Why sunlight is less intense if it hits at an angle

 

Look at the image of the Ukraine flag on the floor. It is much bigger than the size of the original on the window and yet the same light that passed through the original is present in the image on the floor. No extra light has appeared to make it bigger. So the same energy is spread over a bigger area - the intensity is reduced. This has happened because the light hits the floor at a more acute angle.