Hi!

I'll chime in here. The answer is, 'it depends on what your goal is'.

If you just want to get your plants thru the winter in a dormant state, then you really don't need any, or you could use el cheapo fluorescent units (like shop lights) set on 10 hours or less. In late winter, start to increase the daylength to nudge them out of dormancy earlier if you like.

If you want them to remain growing and blooming over winter, you could look into LED and High-intensity discharge lights. Visit some of the Hydroponics websites for these. The 1,000-watt Metal Halide lamps set at 12 hours or so, for example, will get your plants blooming in winter. They will retain many of their leaves at this amount of light. But, these lamps get really hot and your plants will be covered with spider mites by Christmas!

LED lights will be much cooler in temperature. Mites will still be a problem with plumerias actively growing indoors.