If these people walk normally, the vibration from their footsteps will pretty much cancel each other out, and the resulting effect will be weak. If they are soldiers walking in step, the vibration created by each step will be amplified a thousand time and the effect might be such that it could destroy the bridge.
Normal light consist of a bunch of photons with random vibrations, but the laser light has a beam of photons with synchronized frequency, which makes it more powerful than ordinary light.
Now, what happens when we shine a laser on an acupuncture point? The electrons zipping around the nucleus in the atoms of our cells, can absorb that energy. When they do, they assume an orbit slightly higher than usual. When the laser beam stops, the electrons go back to their original position, giving off the energy they have received, a little bit like a guitar string vibrating after being plucked.
That energy is now available for the cells around to use for tissue repair, improving metabolism, etc…
Laser acupuncture does not completely replace regular acupuncture but it is painless, works well with children, and works on areas where needling is contra-indicated such as open sores and infected areas.