I have several young, potted citrus trees that range from 1 to 3 years old that are mandarin, grapefruit, key lime, Meyer lemon and eureka lemon varieties. They spent a productive spring, summer and early fall outside growing vigorously, but are now subject to spending the winter indoors since I live in the greater Seattle area. They are living in a Southern-facing window, but I fear that the constant overcast will not provide sufficient light. What type of light would be best for these young guys to keep up healthy leaf production?
Bare minimum and least expensive are T-5 HO fluorescent, 54 watts per bulb and they can have 2 or 4 or 6 bulbs per fixture. Your little trees should be able to survive for the winter in the window and then be put back out on your covered patio? Deck? Not in direct sun for the summer without acclimation. They will need direct sun to produce fruit...or at least the amount of sunlight you get from a high quality greenhouse skin or covering.
The cloud covering isn't really a problem with light it is the height of the ceiling of cloud cover. Out in Colorado, high ceiling of clouds, you get more light than on the coast with a lower ceiling where the clouds do reduce the amount of light.
I'd be more for stability and staying in one environment to make my citrus happy. If you use artificial lighting you won't have to work so hard acclimating from in to out back to indoors...pictures please and a timeline we can work with? Thanks!