Let us say that I am sitting in a room with all the drapes open. Bright sunlight is coming through the window. The whole room is brilliantly lighted. I will not be able to see the dust particles suspended in air.
Now, if I draw the drapes close, keeping a small slit open, allowing only a beam of sunlight to come in, I will readily see the suspended dust particles in that beam. The same thing will happen in a dark night with the beam of light from a handheld battery torch.
What will be the scientific explanation for this? I can not see the dust particles when I have more light. But when I actually reduce the light and there is only one narrow beam present, I can see those minuscule particles.
How does a narrow beam of light enable me to see those fine elements?