sunlight. It has the best price / benefit ratio (0) and an extremely long operational lifetime (billions of years).

Great! Unfortunately, where I live, this item is out of stock for the next few months

There's no usable sunlight (on skin) for 4 ~ 8 months a year in big chunks of the populated world.

There's a lot of full spectrum lighting options out there since they are used for some other reasons (treating seasonal depression, etc.). Personally, I like this one: https://www.amazon.com/gp/product/B003XDIPNA

A lot of the products require you to sit right next to or put your face right next to them. Think like a makeup vanity. Instead, with that one, I can just set it up right next to my bedside/desk/wherever I'm going to sit on my laptop for the next 16 hours.

I would also like to know. Did a little searching around a few weeks ago and couldn’t penetrate the marketing fluff to get to a trustworthy recommendation.

(Basically looking for a sunlight spectrum bulb)

I would go for the type of bulb you use in aquariums or terrariums.

Those often are missing a chunk of the spectrum algae use… that may not be necessary for humans, but I’d rather get the full spectrum if I can.

My first shot would be a high power, high CRI LED. Something like this [1], but preferably a good bit stronger (or more of them).

1: https://www.ebay.com/itm/352975139212