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Ambient light level is a variable. I have no problem using 150W bulbs in my lights in a darkened room. If the room lights are so bright you can't see the modeling lights they are probably also biasing what you see. If you are using all of the 100% they won't show reflect the ratio. That being the case I would think key light alone might suffice, but that would depend on how you light things.
I use a flashmeter to calculate the light ratios. In my experiments with white lightning, photogenic and alien bees, even with the flash units set so that the modeling light tracks the flash lighting, the ratios are not correct. The incandescent and halogen bulbs do not have a linear output and their output to voltage linearity changes over time as the bulb ages. The only true way to calculate ratios is with the meter.
Anyway, that's how my uncle Monte Zucker did it and it worked for him so that's how I do it.