Shining Light - The Physics Behind This Phenomenon?

Do eyelashes cause a similar phenomenon? How about the iris of a camera?

When you observe this photo, you will see that there is light radiating horizontally and vertically from each light bulb. The light does not radiate in a sphere, but rather in four directions. Also, even though some of the light bulbs are rotated, the lines of light do not rotate with it. Why does this effect occur?

This optical phenomenon is known as “Diffraction Spikes”, and is common in many astronomy photos. The effect is apparent whenever a bright source of light is viewed through a lens with support vanes that obstruct light. This lens can potentially be the lens of a camera, glasses, or even your eyes.

When a lens is directly obstructed with anything thin and solid, light waves will bend around and constructively interfere on the other side, creating thin lines of light in the shape of the obstructive item. This effect becomes more noticeable as the amount of light entering the lens increases. In this case, the diffraction spikes do occur in all of the image’s light, but is only visible for the brightest sources.

In the camera, due to the way the lens was constructed, the lens has support vanes in the pattern of a crosshair. As a result, the interfering light is a horizontal and vertical line.

The item that obstructs the light may be anything thin and solid, even an eyelash. That is why if you squint and look at a bright light, you can get the same effect, due to your eyelashes behaving like support vanes in a camera’s lens.