Be cynical about the math, sure, but if the math works, don't assume technology is useless because it doesn't have a place in a 25 year old's San Francisco apartment.

Lifting 30 kg 2 meters requires about 600 Joules. If it takes 10 seconds to do it, using some kind of pulley arrangement, that's 60 Watts, which is not a strenuous level of effort for a human.

How about doing it continuously?

One 10-second lift every 30 minutes is not "continuously". Also, it would only have to be done when light was needed, i.e., during non-daylight hours when people were not asleep.

it require human energy to power it, which requires food

Humans require food whether they're lifting ballast to power lights or not. How much additional food would they require, if we assume that the entire energy required for the lights is added on (i.e., none of it gets shifted from other forms of exercise)? Let's see.

Suppose the light is in use for 4 hours a day; that means the weight gets lifted 8 times, for a total energy of 4800 Joules. One food calorie (which is actually a kilocalorie) is 4180 Joules. So we're talking less than 1.2 calories per day. What's that, an extra pellet or two of rice?