SPX50 info

Well, after searching for the highly touted SPX50 flourescent bulbs for a
few weeks in San Diego, I finally found it at Specialty Lighting
Distributors for $7.25 each (GE part # F32T8SPX50).  I have it on my
aquarium now, next to a PennPlax Ultra Tri-Lux and a Philips UltraLume.  It
has the same color as the UltraLume, and seems to be the brightest of the
three.  However, since it has a smaller diameter, the light is more
concentrated and I can't really tell which one actually has more lumen
output.  Does anyone have the lumens specs for this SPX50 bulb?