I just potted a butternut squash seedling. The way my patio is situated, it doesn't always get a lot of sunlight - and I think butternut squash requires ~6 hours of it. I was going to go ahead and get a grow light - I've been meaning to get one eventually since there are other plants I want that need a decent amount of sunlight. What kind of wattage should the grow light I purchase have?
Adding to stormy's answer and some comments I recommend using a daylight and warm light bulb mixture to ensure the plant is getting the full spectrum of light. Using just daylight or just warm light doesn't offer the whole spectrum of light that the plant needs when growing. You can use grow lights that use red/blue LEDs since those are the two colors plants need the most. But full spectrum is better yet. The picture below gives an idea of how a warm light and a day light compare (please note these graphs are for LED, but similar results are found in florescent (T5, etc))
For grow lights like what I got from amazon you get something like this...
You can find this grow light (what I got anyway) here. They work pretty good
Another thing that you should keep in mind is brightness and distance. With florescence I know some people have burnt the leaves because of the heat they can give off, so don't keep them uo next to the plant. The grow lights shouldn't do that since there LED and all that good stuff. But not to far away or else the plant will put all its energy into growing towards that light, this is called legging. The perfect distance seems to be a few inches from the plant, or at least having the light cover the whole plant while staying as close as you can.
I think that is all to add on that part, and stormy has some great information so be sure to note that as well!
Picture from this website, nothing from the website aids with answering this question otherwise
Bare minimum grow lights are T-5s; fluorescents, each bulb (4 bulbs) gives 54 watts each and uses a good old boring 110 electrical source, a wall plug in (U.S.) Least expensive in my experience.
Maybe I've missed something but I have never ever known anyone to use a grow light out of doors on a patio.
Your squash needs light. 16 or 18 hours per day. When reproducing that is reduced during the end of a season to 12 hours or less by the sun and the tilt of the planet. That stimulates reproductive growth. Lots of moving air (powdery mildew is rampant on squash talk about later). I do not understand why moving that squash out from under the patio roof is a problem. If you are on the north side of your home in the shade, your squash might produce quite well.
I am having a problem understanding the benefit adding artificial light to plants out of doors. Interesting novel question!