Let's take a closer look at the relationship between light pressure and space dust. We know that, in the earth's orbit, a small particle (dust) of about 0.1 micron in diameter can move toward the sun through a whirlpool motion caused by light pressure. After around 2,000 years, the particle hits the sun. This is called the Poynting-Robertson Effect.

One would think that light pressure would blow space dust far away. Why, then, does it approach the sun? This is because the object is moving, so the direction of the pressure from sunlight is different from the actual direction of the sun. The sun's gravity is stronger than the component of the force trying to repel the dust away from the sun.