Meta comment: I read the article and then did a back-of-the envelope calculation on how much energy you'd get out of one of these. Then I clicked through to the comments and saw that three other comments addressed this.
Good idea, but the physics doesn't work yet. A heavier weight might fix the problem, though. (I use a 5W LED lamp in my apartment that I keep on all the time. It's almost enough for reading and it's certainly enough for walking around at night.)
This thing talks about a 1:600 duty cycle (3 seconds of charging for 1800 seconds of lighting), so, at the very best, it could use a 1.5W LED. Looking a a more realistic 100W human power output (Tour de France riders do 6W/kg or so sustained), it's gets down to .1W or so.
A heavier weight, more height, or more frequent charging all will increase the amount of light produced, but it also means less time to enjoy it.
In the end it all boils down to the fact that a kWh is a lot of energy for a human to produce.
If you're trying to produce light equivalent to what we're used to in first world countries, yes, you're right.
If you're only trying to replace kerosene lamps, you don't need much power. A tenth of a watt with an LED gives a light output comparable to a kerosene lamp. See the numbers elsewhere in the thread.
Good idea, but the physics doesn't work yet. A heavier weight might fix the problem, though. (I use a 5W LED lamp in my apartment that I keep on all the time. It's almost enough for reading and it's certainly enough for walking around at night.)