They are "Light Emitting Diodes" which are pin-head sized wafers of Gallium Arsenide Phosphide layered onto a Gallium Phosphide base. The electron bands in these semiconductors are pulled about by the applied voltage so that "gap" between them is just 2.3 electron volts, equivalent to the wavelength of yellow light (588nm). Electrons from the upper band and "holes" from the lower band anhilate eachother to make the flash of light.
The power dissipation is very low, 0.04 Watts, so that the 30 lights on the stairs take only a total of 1.3 watts, which is quite negligible. There's really no need to switch them off!
They can run on AC power, as the diodes rectify the current natually. I happened to have a 20V AC transformer that nicely runs 10 diodes in series, each having an RMS voltage of 1.8V. This corresponds to a peak voltage of about 3V, not far below the limiting voltage of 3.4V. The reverse voltage can be as high as 5V, so there is no problem with the rectification. The important thing is to wire up all the diodes with the same polarity. If one is wrong none of them will work. There is also a single "test" light position in series with a 1000 ohm resistor, which you can use to test the circuits.
Last updated 4/2/2007