wrecked

It is pretty logical. A bigger ie longer bulb will take more power to drive it.

So in VHO lamps:
59" = 140w
71" = 160w
78" = 180w

or in HO lamps
59" = 80w
71" = 100w
78" = 120w

The lamps in each of these groups will have the same output if they are the same type. For example a Midday Sun VHOR 59" 140w, 71"160w and a 78" (2M) 180w" would all have basically the same output.

For example if your bed is a 40/3 with 20 59" lamps on top with 3 400w facials and 20 71" lamps on the bottom. All the lamps are Midday Sun VHOR's. The total strength of the top would be 4,000watts and the total strength on the bottem would be 3,200watts.