I decided based on this post to build my own SAD lamp. Notes from the article:

• Summer sunlight is about 100,000 lux. An overcast winter day is 1,000 to 2,500 lux. The medical recommendation for SAD treatment is 10,000 lux for at least half an hour each morning. You may need more than this. Typical indoor lighting is 100–500 lux.
• The main supplementation strategy is to fool your brain into thinking it’s summer by simulating daylight for twelve-plus hours, centered around the middle of the day. This means adding daylight-like light before the actual dawn, and/or after dusk. “I turn my bright lights on as soon as I wake up, and as soon as it starts to get dark outside, and also during the rest of the day if it’s gloomy outside. I typically wake around 6 a.m., and run the lights until about 8 p.m, for a roughly fourteen hour artificial day length…Relatedly, it’s important to not expose yourself to bright light, and especially not to blue light, after your artificial dusk time (8 p.m. in my case).”
• Using an iPhone app (Light Meter) pointed directly at the sun today (mid-March), I measure 1875 Lux. This matches the below light setup at about 2.5 feet distance.

I bought 3 of these LED lights and built my own. I don’t have a parts list (I just went to Home Depot and bought stuff I thought would work). But the finished product works well (pictured below).