I've got two of those 100 watters in my veg cabinet along with 8 23watt cfls. Try removing that cover that's in front of the bulb; it seems to block some light. Also, if you're lacking headroom in your cabinet, you can disassemble the whole unit and end up with bulb, socket, and ballast and cut down on the height of the light rig.

I just felt of my ballasts and they are barely warm so no real need to get them outside of the cab.

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