I’ve got something similar to these Party Supplies, Glow Products, Decorations & Novelties
yep, pretty cool. So much so that I stuck it under the binocular dissecting scope at work. The scope has an bright light that illuminates the objects from the top. The light is one of those fairly intense lights found in slide and overhead projectors from my school daze.
When I stuck it under the scope, the blinky refused to flash. As I adjusted the light down in intensity it would flash. As I adjusted it up, the blinky would flash slower and slower. I could control the speed of flashing and could even get the led to flash on and stay on if I timed it right.
PN junctions in LEDs (and regular diodes and transistors, as well) work both ways. If you apply a voltage across them, they emit light. Similarly, if you shine light on them, a voltage is generated across them. In fact, the common photovoltaic cell is little more than a highly modified silicon diode. Blinking LEDs also have a small oscillator circuit right on the die, which contains, among other components, a transistor, probably a bipolar junction type. These transistors are essentially two diode PN junctions placed back-to-back. [SWAG follows] What I think might be happening here is that one of these transistor junctions is absorbing light and generating a voltage across it which, in turn, alters the oscillation frequency until at a certain level, the oscillation stops altogether. The transistor junctions are going to be affected more than the LED junction because the transistor, unlike the LED, is not “tuned” to a particular narrow band of wavelengths. It is more susceptible to a wider range of colors. If you have colored filters, you can experiment with the spectral response to see what colors have the greatest effect.