Posted 22 February 2012 - 10:43 PM
Hi there, this thread might be dead, but its still the top google result when searching for this phenomena. I am a university student taking an Atmospheric Radiation class where we are learning about interference and scattering of light. Two days ago I experienced the eye-halo phenomenon while in a bathroom in Vegas over the weekend. I have never seen it in my own bathroom mirror. My professor who is supposed to be an expert on this hasn't heard of it before, but we talked about it.
There are definitely still a few mysteries about this, but allow me to explain what I do understand. This is a "glory" type effect. Light coming straight at a foggy mirror is scattered in all directions by droplets floating in the air (steam), longer wavelengths scatter farther (red has a long wavelength). Then this scattered light is reflected back by the mirror. So its actually happening all over the mirror, but scattered light of all colors all reflected back looks like plain white light, the normal case. However, your eye is small so if you are sort of in the line of sight of the light source (doesn't have to be right behind you, but if the mirror can see like a light right above your shower opposite the mirror that's good, if you only have lights above the mirror it should not be as good, but still possible), you'll see the way its light is being scattered preferentially based on wavelength. It is an observer effect, has nothing to do with eye color, so a person with one totally identical but glass fake eye would only see the eye-glory in their working eye. Two people in there should only see glories in their own eyes, not each others.
Light is scattered in this way (Mie scattering) when the scatterers are close to the size of the wavelength. Since visible light has very tiny wavelengths, abnormally tiny steam droplets floating in the air may be what causes this. It's possible it also has to do with the size of the droplets on the mirror, but I'm not sure. A mirror with a thin film of soap left on it will not fog so much and will have big droplets. A dirty mirror also will have big drops. A very clean mirror should make the smallest drops, perhaps why many of us saw this in hotels and not at home where the mirror might not be cleaned as often. But this may have more to do with floating steam droplets than the ones on the mirror. A way to make floating droplets very small is to have small particles for them to condense on already in the air, this is known in the atmospheric science community as the "aerosol effect". Aerosol particles like smoke would help, so I wonder if those who have seen this are smokers or used an aerosol spray before taking the shower? A good experiment would be to smoke in the shower room right before taking the shower, which is what I did in Vegas that I don't normally do at home.