Its a myth that DE lamps produce more light than SE lamps.
"Comparing the data here and other 250W DE articles with the data for 250W Mogul lamps, should provide enough factual information to dispel the myth that 250W DE lamps produce more light output than the 250W single ended mogul lamps. A general sweeping statement to this effect cannot be made, and depends on the lamp under consideration"
http://www.advancedaquarist.com/issu...04/reviewb.htm