When I was researching them (several years ago now) the only key thing that everyone agreed on is that they have to be really honkin&#x27; bright, with 10000 lux at 2 feet being the standard.  You&#x27;ll need even brighter bulbs for your scheme, since you&#x27;ll be placing them further away.  It&#x27;s an inverse square relationship, so at 6 feet you&#x27;ll need a 9x as bright bulb.