While at one of those glow in the dark putt-putt places with the family I noticed something strange. I happened to look up directly into one of the blacklight fixtures. It was like I was looking through slightly frosted glass. As I turned my head to look around the room, the effect went away. Looked back up there it was again. If was almost like there was an angle I would cross and then this effect happened.
So what was it? I wondered if the UV was “lighting up” my future cataracts (I’m 45).
My guess is that, since you are looking into something so far into the blue-end of the spectrum, your eye lens was somewhat out of focus.
I’ll let someone who can describe optics better explain.
Here is something that may describe the effect you describe:
http://www.nikon.com/products/sportoptics/how_to/guide/binoculars/technologies/img/technologies_08/pic_008.jpg
As you look away, the far red and far blue focal points are closer together, making a sharper image.
How is it even safe to look at those black-lights? That’s UV going straight into your eyeball, isn’t it? After all we’ve been warned about the dangers of UV light to the eyes!
Or is it not really UV enough? Is it really just a really deep purple just a bit beyond what we can see?
The explanation I’ve heard is that your eyeball actually is slightly fluorescent (perhaps just the vitreous humor, lens or cornea), and you’re perceiving that glow. To check that out, go to the putt-putt place with someone and have them look into your eyes.
Damage done by EM radiation is the result of two processes. The first and most obvious is, of course, bombarding something with so much energy of any wavelength that the object heats up. The second and more insidious damage is due to the photoelectric effect, by which EM radiation ejects electrons from their stable low-energy orbitals, changing the geometry of the chemical bonds. The photoelectric effect requires a minimum energy, below which the electron is “jostled” (creating heat) but is required (by the Pauli exclusion principle) to return to its original position. This minimum energy, called the “work function”, varies between materials but is typically in the mid UV range. Any radiation above this amount of energy is considered to be damaging “ionizing radiation.” Below this level, electrons cannot he ejected and ionization does not occur.
Black lights work in the very near UV, and exploit a similar effect which bumps electrons up a few energy levels without ejecting them, but those electrons almost immediately fall back to their original level, releasing energy in the form of visible light which you perceive as fluorescence.
Interesting, next time I’m there I will definitely do that.