Yes, I'm afraid it is not quite as simple as that. Let me see if I can do it using math as an example. You know that if you square a number, say 2, you get a positive number always? Like for instance -2 times -2 = +4. OK.
Now think about square roots. I can take the square root of +4 and get +2 right? OK.
But what is the square root of -2? Can't be done because it results in what's called a 'non-real' number.
If you imagine a simple plane, like a graph, it's got two axes, right? An X and a Y. You can plot any point simply by taking the X coordinate and the Y coordinate and finding where the two lines meet. I'm sure you all did this in school . . .
Now, imagine a point that lies not ON the paper but, say, behind it or in front of it. That would be an 'imaginary' number.
The current flow in an inductor - like a lamp ballast - if you connect it straight across the supply, with no load (no lamp), would be like the point that's not on the plane but behind it.
From Wikipedia:
The significance of power factor lies in the fact that utility companies supply customers with volt-amperes, but bill them for watts. Power factors below 1.0 require a utility to generate more than the minimum volt-amperes necessary to supply the real power (watts). This increases generation and transmission costs. For example, if the load power factor were as low as 0.7, the apparent power would be 1.4 times the real power used by the load. Line current in the circuit would also be 1.4 times the current required at 1.0 power factor, so the losses in the circuit would be doubled (since they are proportional to the square of the current). Alternatively all components of the system such as generators, conductors, transformers, and switchgear would be increased in size (and cost) to carry the extra current.
Utilities typically charge additional costs to customers who have a power factor below some limit, which is typically 0.9 to 0.95. Engineers are often interested in the power factor of a load as one of the factors that affect the efficiency of power transmission.
Now, if you are running say 3KW of inductive ballast lamps in your house and the rest of your load is say 3KW, then I can say for sure your power factor is not 0.9 or 0.95!
I could calculate it for mine, if I am not too lazy. But I only run 300W of lamp loads via inductors, so I am not bothered.
By the way, fluorescent lamps also are inductive loads. CFLs are not.
All the above is only really of interest to those who are running large lamp loads, say 4 KW or more. YOU might not worry but if there are neighbours with grow setups also running inductive ballasts . . . it all adds up.