Two charges, one curve
A commercial bill usually has an energy charge and a demand charge, and they read different features of the same load curve. Energy is the area underneath it. Demand is the highest point. Four zones of 2.25 kW on a 16 hour photoperiod burn 144 kWh a day whatever time they start, so the energy charge is fixed the moment the photoperiod is chosen. The peak is not fixed at all.
Start all four together and the lighting peak is 9 kW on top of a 3.2 kW base, so 12.2 kW. Start them six hours apart and at no moment are more than three lit, so the peak is 9.95 kW. Same hours, same kilowatt hours, 2.25 kW less on the meter, and at 14 dollars a kilowatt that is 31.50 dollars a month for changing four timer settings.
There is a floor, and it is arithmetic
Four zones times sixteen hours is 64 zone-hours that have to fit into a 24 hour day. Divide and you get 2.67, so at every moment at least three zones must be lit — you cannot arrange 64 hours of lighting into a day with only two on at a time. That rounded-up figure is the floor, and no offset beats it.
The page finds the floor two ways and prints both. It sweeps every offset from zero to 24 hours in quarter hour steps, walking all 1,440 minutes of the day for each one, and it computes the zone-hours division directly. When the two agree, which they should, the sweep has confirmed the arithmetic rather than replaced it.
When staggering is worth nothing
Push the photoperiod up and the floor rises with it. At 18 hours across four zones the floor is three; at 20 hours it is four, and every zone is lit at some common moment no matter what you do. Two zones on a 16 hour photoperiod have a floor of two, so there is nothing to gain there either. Staggering pays when the total zone-hours leave slack in the day, and the amount of slack is visible in that one division.
The part the arithmetic does not decide
A stagger is a set of dark periods scattered across the clock. Somebody has to work in those rooms, and a zone that goes dark at four in the afternoon is a zone that gets harvested under a headlamp or not at all. Crops differ in whether the timing of the dark period matters to them, which is a question for the grower and not for this page. And tariffs carry ratchets, measurement intervals and time of use windows that a single dollars-per-kilowatt figure cannot represent. What this gives you is a kilowatt number to take to the tariff sheet.
Questions people ask
Does staggering the lights save energy?
No, and the page says so on its own line. Every zone runs the same number of hours whatever the offset, so the kilowatt hours and the energy charge are identical. The only thing that moves is the peak, and therefore the demand charge. If your tariff has no demand charge, staggering saves nothing at all on the bill.
How low can the peak go?
To the floor set by the zone-hours. Multiply zones by photoperiod hours, divide by 24 and round up, and that is the fewest zones that can ever be lit at once. Four zones at 16 hours gives 2.67, so three. The page computes that directly and also finds it by sweeping every offset, and the two agree.
What offset should I use?
The sweep reports the one that gives the lowest overlap, which for evenly matched zones is usually the day divided by the zone count. Whether it is usable depends on when people work, when deliveries go out and what the dark periods land on. The page gives the electrical answer and stops there.
Why does the hourly table sometimes disagree with the headline?
Because the table samples on the hour and the peak is found on the minute. An overlap that opens at 6:15 and closes at 6:45 is real, counts on the meter, and appears in neither the 6:00 nor the 7:00 row. The headline figure is the one to trust; the table is there to show the shape of the day.
Is a demand charge really worth this much attention?
That depends on your tariff, which is why the rate is a field. On a bill where demand is a small fixed charge the answer is no. On a bill where it ratchets — where one high month sets a floor for the following eleven — a single afternoon when every zone happened to be on together can cost more than the change in timer settings would ever have saved. Your tariff sheet says which one you are on.