Oh boy, I want one of these. This would absolutely perfect for winter depression (I suspect much better than the "SAD lamps" marketed for this purpose which are bright not even close to this bright). But £889 is a lot of money for a lamp!
Find a garden shop, a 2' square full-spectrum light from "The Indoor Sun Shop" was very important to my mental health when I lived in Seattle and cost a lot less than this. Especially after I added a mechanical timer so I could never be too depressed to turn it on in the morning.
If you're not afraid of DIY and it looking (much) uglier than these lamps, you can buy extremely bright "cob lights" and make something yourself: https://meaningness.com/sad-light-lumens