Now there's a trick question if there ever was one!
For fluorescent lighting calculations, you use the figure on the ballasts, rather than adding up light bulbs.
For traditional ballasts and when using T-12 lamps, yes, volt-amps can be treated as watts.
The same applies for any fluorescents on single-phase systems.
However- on some fixtures you will see a sticker warning you about sharing the neutral wire between different circuits. This sticker is a major clue that not only are the ballasts electronic- but that "harmonics" may be an issue. And, since with three phase systems no single leg can completely "cancel out" another, you will want to up-size the neutral, or run separate neutrals.
All fixtures using the narrower T-8 and T-5 lamps use electronic ballasts.
The explanation here as to "why" volt-amps and watts are not the same is that the distorted waveform can fool an amp meter into reading lower than the actual current being used.
