Step-by-step instructions on how to make a DIY LED panel with parts list ...
https://www.ledsupply.com/diy-makersled-led-grow-light
https://www.instructables.com/id/Introduction-to-LED-grow-lights/
If I would really want to do this, I probably could (the soldering, etc). But finding the right parts that cover the right spectrum, etc, would be a PITA I don't have the energy for. My initial plan, a couple of years ago, was to buy a couple of blue, red and white LED strips and then use them in a custom-built closet of sorts.
I have to wonder how much more energy efficient these DIY LED setups are when compared to now commonly available white LED bulbs. I fully understand the green portion of the light is "wasted" but using common bulbs and fixtures is cheaper and certainly more convenient.
That's what I'm using to help my plants through the dark days of winter.
Yes, thought about that too and tried it out last winter with a cold (bluish) and warm (reddish) LED lamp. It didn't seem enough to grow seedlings, but maybe I did it wrong.
Like I said, there seems to be more on offer, but very little info, everything China-made, nothing where you go 'hey, that looks trustworthy'. So, unfortunately, it seems I have to go the Amazon route, where I can at least check out user experiences. This
grow light is popular and has a 3 year warranty and good customer support:
What I like about it, is that it has separate buttons for the early growing period and then the blooming period. Reviews also look good, but it's a bit pricey, at 90 EUR.
have you tried winter sowing?
Well, with some plants, and we also have cold frames. But my wife wants to have a head start before spring starts, by having seedlings ready to go out as soon as there's no more chance of night frosts. So far, every winter, all the stuff she planted out early in the house, got spindly, stunted growth, etc. And then she'd feel she was behind with everything for the rest of the growing season, apart from all the wasted work.
Hence, a good grow light that covers an area of about 3x3 feet.