Have you checked the lamps in the Source 4's to make sure that they are indeed 750
watt lamps?
Are the
throw distances the same for both kinds?
Are the degrees the same?
From the manufacturers data sheets:
Strand 26 deg with 575w GLC - at 30' = 13.9' Beam and 216 fc.
Source 4 26 deg with 750w
HPL - at 30' = 13.4' Beam and 196 fc
As we can see the
Strand unit produces a larger beam and 20 more
foot candles.
Strand 26 with 575w GLC at 45' = 20.8' beam and 96 fc
Source 4 26 with the 750w
HPL at 45' = 20.1' beam and 87 fc
Here note that the difference is smaller than before, but there is still a difference of 9 fc.
I'm actually surprised here, I figured that the Source 4 should be brighter butthey simply are not.
It appears that the
Strand unit is just not as good as the Source 4 at throwing long distances.
It is probably something to do with the actual lamps and design of the fixtures.
You can try benching them properly to get the most light out of the
fixture.
Edit: If it is really a concern you can try buying some GLA lamps - these are the long life version of the lamps used in the
strand units. Like the long life lamp for the source 4, they produce less lumens so they will ultimately be darker on
stage. I'm not sure on the calculations needed to see how much less however.