Jolly Jill asked about making a "universally recognized unit of 'energy consumed'" rather than the Calorie — something like a battery or a gas-can or an apple. Here's my e-mail response:
I took a closer look a this and tried to make some kind of "energy currency." It is valuable to keep things at a human-level, so a 100-Calorie apple seems to be a good choice. A 2.75-inch apple has about 100 calories. Conveniently enough, a peck contains about 25 of these size apples and a bushel, about 100.
For a smaller unit, a grape has about 3.4 calories (about 4 watt-hours) so 30 grapes (or maybe 5 6-grape bunches) makes one apple. For purposes of LED's, though, we're talking about 0.05 Calories or about 1/66th grapes. Thus, an even smaller unit could be a drop of maple syrup. There's 200 calories in a 4-tablespoon serving (so that's 16 Calories per teaspoon) and I put a little more than 12 drops into a 1/4 teaspoon, so each drop is about 1/3 Calorie (0.4 watt-hours); 10 drops makes a grape.
A candy sprinkle is about 0.07 inches across so about 877 fit in a teaspoon making each of them (assuming they're made entirely from sugar) about 0.018 Calories each so there's 18 in a drop of syrup. Let's call it 20 sprinkles, so 960 would fit in a teaspoon and each is 1/60 Calories. So now we've got:
- 1 sprinkle = 1/60 Calories
- 20 sprinkles = 1 drop of maple syrup = 1/3 Calorie
- 10 drops maple syrup = 1 grape = 3.4 Calories
- 6 grapes = 1 bunch of grapes = 20 Calories
- 5 bunches of grapes = 1 apple = 100 Calories
- 25 apples = 1 peck of apples = 2500 Calories
- 100 apples = 1 bushel of apples = 10000 Calories
I'm afraid I'm going in the wrong direction with this. Although it's neat to see the conversions, I think it makes things _less_ intuitive — calorie numbers may be best because they're compact to represent. This may be a useful way to get people to think about calories, though … like an LED can run for an hour on the energy in 3 candy sprinkles, or that it takes 3 bushels of apples to match the energy in a gallon of gas.