Do you see diffraction occurring on an everyday basis? What is more common to see is the effect of light travelling in straight lines. We can tell that this is happening because of the many shadows produced in a room or anywhere light falls. We don’t normally observe diffraction and interference because the wavelength of light is so very short.

In order to see the light spreading, it would need to pass through openings that have very small widths. When can you really observe this? Only when the width of the opening is almost the same as the wavelength of the light.

Look at this interactive video that shows how diffraction changes as the slit width changes.

You should notice that as the slit width decreases down to be about the same value as the wavelength, that the spreading is more pronounced. Most openings that we see light pass through are doors and windows. Theses have a width of roughly 1 meter. Since the wavelength of light is between 400-700 nm, these openings are too small to notice any type of diffraction. This is why the light appears to travel in straight lines.