There are plenty of tanning (UVB) lights at all different wattages available for purchase.

I think the problem is the visible light output tends to be harsh, and the bulbs are highly inefficient, they are exensive, and they don’t last very long either.

So there would be a lot of problems to solve, not the least of which is the cultural issue you raise of scaremongering around UVB exposure in the first place.

There is one FDA approved vitamin D lamp made by Sperti.com. Costs about $400, has a 5 minute timer, instructions say to use it once every other day, the UVB spectrum of the lamps is tailored to Vitamin D production. I have one, it works better than pills.

For those curious about the lamp, this is the link: https://www.sperti.com/product/sperti-vitamin-d-light-box

They used to sell these (as regular-size fluorescent tubes) decades ago.

Or just replace window glass with OP4 plastic. Not cheap.

I try to use a tanning bed a couple times a week in winter.

I think we need to update GTL: Golang, tan, laundry.

is that safe?

Tanning beds are banned in some countries with high skin cancer rates for good reason. It is a lottery and you are accumulating risk with exposure. I strongly suspect (without any real evidence) that there are a number of beneficial health effects to moderate UV exposure that can improve quality of life for some people but the experience with fair skinned populations in high UV parts of the world has been overwhelmingly negative. The public health advice is basically written in blood on this topic and so I would view people and sites promoting alternative views with an appropriate amount of skepticism for now.

Not at all.