Next to my bed I have a fluorescent desk lamp. One night, after I had turn off all the lights in my room, I grabbed my blanket from the other end of the bed. As I grabbed the blanket, one end of the blanket swept underneath my lamp. I was surprised to see a few faint flickers of light come from the light bulb. I tried waving the blanket underneath the lamp again and the same effect happened. I tried it again using my hand instead of the blanket, but the lamp did not flicker that time. Is there an explanation for this strange phenomenon? As a side note, the blanket never touched the bulb and it was swept about 6 to 18 inches underneath the bulb.
[Physics] Unusual phenomenon from fluorescent lightbulb
everyday-lifevisible-light
Related Solutions
A fluorescent lamp or fluorescent tube is a gas-discharge lamp that uses electricity to excite mercury vapor. The excited mercury atoms produce short-wave ultraviolet light that then causes a phosphor to fluoresce, producing visible light.
Taken right from Wikipedia! http://en.wikipedia.org/wiki/Fluorescent_lamp
End of life
The end of life failure mode for fluorescent lamps varies depending on how they are used and their control gear type. Often the light will turn pink (see "Loss of mercury" section for details) with black burns on the ends of the lamp due to sputtering of emission mix (see below). The lamp may also flicker at a noticeable rate (see "Flicker problems" section for details).
Mercury is slowly absorbed into glass, phosphor, and tube electrodes throughout the lamp life, until it can't function.
The failure symptom cycle starts out with a flicker (run-up time to full light output). When the mercury runs out (absorbed by the glass, phosphor, and tube electrodes) the lamp glows a dim pink and the argon base gas takes over as the primary discharge.
The same effect can be observed with new tubes. Mercury is present in the form of an amalgam and takes some time to be liberated in sufficient amount. New lamps may initially glow pink for several seconds after startup. This period is minimized after about 100 hours of operation.
To complement Floris's answer, here's a quick animation showing how the shadow changes with the size of the light source. In this animation, I've forced the intensity of the light to vary inversely with the surface area, so the total power output is constant ($P \approx 62.83 \, \mathrm{W}$). This is why the object (Suzanne) doesn't appear to get any brighter or darker, but the shadow sharpness does change:
In this scene, the spherical lamp is the only light source, except for the dim ambient lighting. This makes the shadows very easily visible. In a real-world scenario with other light sources (windows, for example), the effect would be less pronounced because the shadows would be more washed out.
The following animation shows the scenario Floris described, with a rotating long object:
Best Answer
I would guess that what you saw was due to static electricity. Your blanket must have been slightly charged and when you moved it below the bulb an induced emf caused the flicker of light.