This might be an example of an "after image" that occurs after our eyes have
become dark adjusted, then the eyes observe a reasonably bright light
followed by a return to darkness.
* * * * after image fun * * * *
The way I think is most fun (and eerie) is to take a flash (photographic
strobe light) into a dark room as described, and simply aim it at some
object and flash it while looking in the direction of the object. (That is,
we're not aiming the flash at our eyes, we're using it to momentarily
illuminate something in the room). After the flash, "keep looking" and you
will see the object reappear in a ghostly manner... usually bluish white.
If you turn your head the image will move with you because it is all in your
eyes at that point.
For a bright and persistent after image the object being flashed needs to be
within a foot or two of the strobe, and observers should also be within a
few feet.
It is fun to flash the while aimed at a hand, palm facing you, fingers bent
as if getting ready to grasp something. When the after image appears it
looks like the ghostly hand it aiming to grab your face, and if you turn
away it's still right there waiting to grab you.
* * * * back to Bill's question * * * *
The "experiment" referenced by Bill Beaty sounds more like an afterimage
than phosphorescence, but that's purely a guess on my part. I admit I am
not curious enough to try it as suggested, but I have flashed the strobe
"through my hand" to see if I get an after image, and I do. A bright enough
flash would work even through your arm and with your eyes closed. Indeed,
if you flash the light toward closed dark-adjusted eyes, the afterimage is
quite eerie because you are looking at your eyelids and sometimes seeing
blood vessels, etc. in your eye lids.
A way to test if this is afterimage as opposed to real phosphorescence would
be to observe the image and move the arm while observing the image. If the
image does not move with the arm you are seeing the afterimage. If the
image does move with the arm it would seem you are indeed observing the arm.
The after image phenomenon also does not go away if you close your eyes.
However, it seems some people see the after image better with open eyes
because it seems their minds play tricks on them. If you close your eyes
you're not expecting to see anything, and sometimes you don't. If your eyes
are open in a dark room after having been flashed, you brain-eye system is
consciously looking to see something and typically does.
Michael D. Edmiston, Ph.D. Phone/voice-mail: 419-358-3270
Professor of Chemistry & Physics FAX: 419-358-3323
Chairman, Science Department E-Mail edmiston@bluffton.edu
Bluffton College
280 West College Avenue
Bluffton, OH 45817