LED for flowering?

Has anyone tried any of the High Powered LED lights for flowering? Does it take longer? A significant loss in yield? I am looking to do this in a very small space 3x3x3 where plant height would be a problem factor for regular HPS lights - the genetics are master kush from clone, which can stay prety short as far as i know, let me know your thoughts guys..

my thoughts are that the LED lights would be a big waste of time and money. . there is nothing worst than taking care of a plant for three months and have it not fill in with dense nugs. . especially a kush strain which is what will happen if you choose to go with LED.. have you thought of a smaller HPS light. . air cooled. . ?