I would suggest grabbing a UV bulb from a local store or ordering one online along with an aluminum cooking tray/sheet, anything to bounce the light back toward the object. You can then just use an every day desk lamp. The process will take quite a bit longer than the summer sun but I think you'll like the end result. I did this to a bunch of keycaps with a few cleanings and repeat application of some peroxide cream and about 3-4 days later they were perfect again without the bleached look you get from harsh sun exposure (I live in the South).

What are you using for Retrobright? Here in the US I got a bottle of Salon Care women's hair product for 5 bucks.. Worked great!

Also: I would be interested to know if your basic black light bulbs would work. I'm not exactly sure as to what UV spectrum it actually needs to work. I bet a cheap black light bulb would just take a bit longer. I have some 30 dollar LED plant grower bulb I actually ended up buying from some tobacco store when I did this.

8-bit Guy, has found that heat instead of uv-light, works just as well in some cases. And even better than uv-light in some rare cases. To make it short, he simmered/boiled some keycaps on the stove in hydrogen perioxid.

I'm using regular "black light" UV fluorescent lamp for something like 20 bucks including frame, and it works. When purchasing another UV light source, get the UV-A type. UV-B or UV-C are not appropriate (and they're more dangerous as they could do some damage to your eyes).
As for the heat, the chemical reaction that retrobright is based on speeds up at higher temperatures, that's why sunny days work the best.
Be careful when attempting to heat old plastic, it can melt at surprisingly low temperatures 😀

I've been thinking about buying one of the ozone generator things 8-bit Guy used, since it is much less messy and should cover more evenly. There are similar machines on Amazon for $50:

https://www.amazon.com/Generator-machine-Ster … ozone+generator

My idea is to get a large transparent plastic bag, put any yellowed plastic parts into it (even a whole PC case if necessary), fill the bag with ozone and seal it up.

In the summer, I could just put it outside in the sun, and it should work pretty well.

In the winter, I could probably get a large cardboard box, line it with reflective foil (probably be easiest to unseal the seam on the box and then put it back together after it is lined with foil), and put a UV light in the box, along with the bag of ozonated plastic.

I haven't done this yet, but I'm accumulating enough old yellowed computer stuff that I think it'd be worth it to invest in one of the machines. The convenience of not having to slather goop onto electronics (and then worrying about streaking or unevenness) is worth the higher initial outlay of money, and the machine will probably last longer than $50 worth of salon care stuff.