When I was looking into them I noticed that they were labelled (maybe not at Radio Shack) by the "spread" or degree/angle of light out put.
IE a 30 angle would be a "spotlite" effect, narrow beam.
Then there was a 60 angle that spread the light out more.
They are also sold by the light output/rating.
I'm not sure of the exact rating that closely resembles moonlight