How many lux do I actually need for a SAD lamp to work?

The widely cited clinical figure across the reviewers we read is 10,000 lux measured at the distance you actually sit. Specialist-community threads (notably r/HubermanLab and r/askportland) emphasize that the rated lux often assumes you are only a few inches away, so a lamp with a larger light face and honest output at 12–14 inches is generally more usable than a small panel rated 10,000 lux at point-blank range.