Light cannot be pressure for we should see in the night as well or better in the day we should be a bright light above us because we are pressed downwards... there could be no refraction since same matter cannot press 2 ways. a little body interposed could not hinder us from seeing pressure could not render shapes so distinct. sun could not be quite eclipsed Moone & planets would shine like suns. When a fire or candle is extinguished we looking another way should see a light.