I would like to ask is there a way to convert Blenders Lamps (Area/Spot) from power level to Watts or Luminance, (Candles) I do have an image where I'm trying to make a spot lamp on the back of a house (night time View).

But cant seam to get the effects right, I do understand that external rendering programs can pick some of this up but if i don't get it right in the first place any external render software wont fix a total mess to start with

I made a lamp type hood and used Area lamp due to the diffuse effect and estimated the power for cast soft displacement of light over the scene

Please advise any help is welcome Pic of part of the scene http://blenderartists.org/forum/showthread.php?266254-Lighting-Shadows
Render with blender render so-far.

Thank you for time to read this and any advice you can pass on

I don't know where the guy got it, but he says that energy level is in Watts. http://www.blender.org/forum/viewtopic.php?t=25182&highlight=python+lamp