We have done a small amount of work with LEDs over the last few years and have discovered the following when putting together luminaires:
The lumen outputs of LED datasheets are notoriously misleading. The problem is that the LED is a bright point source of light and not a distributed source.
Also the lumen output from the luminaire is often not measured - only the theoretical lumen output from the LEDs used in it. This is now being addressed with energystar rating system which has just recently been nailed down. And longevity is way overestimated unless you can seriously liquid cool the LED junction - also longevity was specified as time to reach 60% initial lumens compared to 80% in longevity specifications for SON-T lamps.
Output listed in datasheets is often from a brief flash of light in an integrating sphere which differs significantly from output in typical applications where Tj is never 25C.
Also best efficiency has often been running at 65% of rated power on very high specification heatsinks, at least the big manufacturers are learning this now and not pushing the LEDs so hard (also helps with thermal issues generally).
Reflected light is nicer on the eye but requires significantly more lumens to acheive good standard desk lumen levels of 300. Point source lighting from direct viewed high brightness LEDs will leave persistence spots on your retina - like seeing stars - usually not dangerous unless you stare long and hard at close range! There were some guidance documents beginning to appear on this topic when we were doing our development work.
My advice would be use reputable reliable LEDs from established manufacturers, run at 65% of rated power, properly thermal bond to high specification heatsinks, feedback heatsink temperature (from as close to the LED as possible) to your control circuit in an attempt to limit Tj and promote LED longevity and concommitent lumen output.
If you want a good result that will last then good design and a healthy bank account are essential I think.
Hope this helps.
The meaning of life is a blank sheet; write on it wisely. ~ M.Cutler.