On our A/C (B737-200) most have pulse lights installed. They are very effective as you have mentioned and function as follows.
They have a seperate switch on the overhead lighting panel which when selected ON and the landing light switches are OFF causes the inboard and outboard landing lights to pulse. Pulsing can be stopped in one of two ways, by turning OFF the pulse lights or by turning ON the landing lights, obviously when the landing lights are selected ON then the lights stop pulsing and remain on steady.
Hope this explains in Readers Digest format how the system works.
BTW the bridge you are watching from is that the (in)famous 14th Street Bridge that claimed the Air Florida B737 back in the 80s ??
[This message has been edited by Canuck_AV8R (edited 26 March 2001).]