I work from home in an area that gets high amounts of fog, and I frequently go days without seeing the sun.  I can confirm that I seemed to need about 10k lumens before making an noticeable change in mood.<p>I used three (1 warm, 2 cold) relatively inexpensive 36W LED bulbs from ebay locally - <a href="http:&#x2F;&#x2F;www.ebay.com.au&#x2F;itm&#x2F;121704759594" rel="nofollow">http:&#x2F;&#x2F;www.ebay.com.au&#x2F;itm&#x2F;121704759594</a><p>(Note they are LARGE and require a free-standing light fixture without any type of lampshade)