Found this today, and thought it might be worth sharing as a graphic representation of what's already been said:
Originally found at http://4.bp.blogspot.com/_VyTCyizqrH...nsperwatt2.gif
1) This describes only lumens (brightness as seen by the human eye) produced in all directions.
2) It doesn't address PAR (brightness as "seen" by plants), although lumens and PAR are at least loosely correlated in most cases.
3) It doesn't address reflectors. Lights typically radiate in all directions, and we need to redirect that into a narrow beam. Some light is inevitably lost in the process. Lights like linear T5's end up being more efficient in aquarium use because they have shaped and mirrored reflectors available which lose little light. Other lights are harder to design efficient reflectors for. LEDs are a unique case, they don't need reflectors since they already radiate in a narrow beam; so no light is lost at all.
4) I'm not sure how old this chart is, so it may not represent recent advances in LED lighting. LED efficiency continues to improve. Efficiencies as high as 135 lumens/watt have been reached for white LEDs in the lab, as documented here
; which meets or exceeds the efficiency of all other lighting types even before considering the advantage of LEDs not needing reflectors. We'll probably all be using LEDs in 10-20 years.