| MadSci Network: Physics |
The question: "Why does light reflected from a cylindrical object project a 'heart' shape? For years, I have noticed that light reflected from a cylindrical object (e.g. a metal ring, a mug, a metallic watch rim) projects a double-arch 'heart' shape in the middle of the circle. While many websites talk about reflections from concave and convex mirrors, I have not yet been able to find one that demonstrates what happens when the mirror is a complete circle. How does this 'heart' pattern emerge? Can it be predicted / calculated? Thanks!"
Indeed it can be predicted / calculated! I use an optical design program called Zemax, with which I "built" a model of the situation you are describing. I "made" a light source that has 41 parallel light rays going from left to right, these rays impinging on a concave hemispherical mirror. The 41 rays reflect off the mirror and end up going roughly right to left. The result:
You can clearly see the "heart-shaped" area of light. The results of Zemax are exact (to the precision of the math of the computer being used!), so the result you see here is truly representative of what you would see in the real world (assuming a perfectly shaped reflector and a perfect collimation of the light source).
John Link, MadSci Physicist
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