If your camera is pointed at the back wall, it may well be the angle of incidence.  The bulbs are hitting the wall at close to 180% (vs. the camera) and so look much brighter.  Try shortening the range so it just hits the back wall and applying 100% range falloff.  This should light the side walls, but not over-light the back one.

As a test, turn toward a side wall and see if it doesn't render brighter.

Klebnor

Lotus 123 ~ S-Render ~ OS/2 WARP ~ IBM 8088 / 4.77 Mhz ~ Hercules Ultima graphics, Hitachi 10 MB HDD, 64K RAM, 12 in diagonal CRT Monitor (16 colors / 60 Hz refresh rate), 240 Watt PS, Dual 1.44 MB Floppies, 2 button mouse input device.  Beige horizontal case.  I don't display my unit.