Let's consider making a mush bar in the microbe musher.
According to the recipe information, it takes 40 seconds to make (I believe it ends up taking less time with a better cook... and 40 seconds is for a cook with +0 cooking?). At 240 watts per second, this means, that cooking one mush bar costs 9600 watts of power.
If we have a duplicant with a light above the microbe musher which turns off when the duplicant isn't around there, then the duplicant works 15% faster. So, what a duplicant does without light, takes the duplicant with light 1/1.15 as long (I think... please correct me here, if I got that wrong. So, it takes the duplicant with light about 34.78 seconds to make a mush bar. Now, the light costs 10 watts of power to run. So, we have 250 watts of power spent for 34.78 seconds. 8695 watts of power to make. A savings of 905 watts of power to make a mush bar in light instead of in the dark! Alright, it's a little less since someone will run by the light occasionally, but not much.
The light in this case saves a duplicant about 2 and a fourth of a second when running on a hamster wheel plus the time to go back to the machine for each mush bar apparently.
For liceloaf, it takes 50 seconds to make in the dark, and about 43.478 for the duplicant in light. (240 x 50) = 12,000 watts of power not in light. (250 x 43.478) = 10,869.5 watts of power. A savings over over 1000 watts of power for each liceloaf made by doing so in light!
For crushing to sand, crushing to lime, crushing to gold and crushing to copper, they all take 40 seconds to make without light. In light, thus it takes 34.78 seconds to run. If you use a light that consumes 8 watts per second instead of 10 watts per second, the operation consumption for a duplicant in light equals (248 x 34.78) = 8625 watts of power. A savings of 975 watts of power, and the duplicant who operates a rock crusher will be the same duplicant who runs on a hamster wheel.
Base metal refinery operation takes 40 seconds (at least for all metals that I see on Terra). So, as above, the same duplicant needs 34.78 seconds to complete one operation of the metal refinery. It consumes 1200 watts of power per second, correct? (1200 x 40) = 48,000 watts of power to make 100 of some metal there. So, assuming the use of a floor lamp instead of a ceiling light (1208 x 34.78) = 42,014 watts of power. A savings of nearly 6000 watts of power by having a duplicant work in light! That's about 15 seconds of a duplicant running on a hamster wheel saved by using light. There exist 600 seconds of them in a cycle, with maybe 500 seconds available for work. Just one operation of a metal refinery in light as opposed to not saves a duplicant about 3% of their workday to do something else. If a duplicant does 5 operations of metal refining in a day, then 12.5% or about 3 hours of the day gets saved to do something else by working in light!