Need Help lamp distance

[kcollinsdesign]

Is there a general rule of thumb for how far a sign face should be from the lamps for even illumination? I currently have a project involving a 3' x 10' x 9" deep wall mounted cabinet that needs a new face. The t12 fluorescent lamps are about halfway in, about 4" from the face. The sign currently has a flat face, but it is hard to tell if a new .177 polycarbonate face could be used or if the client will need a pan face (the client wants to do their own installation, the sign needs relamping, and I'm trying to avoid an hour long field survey at night).
Naturally, the client does not want to pay for a pan face. I know I can re-wire the cabinet to put the fluorescents at the back of the cabinet, or that I could remove the fluorescent lighting and install LEDs. Perhaps a flat face will be fine 4" from the lamps. Any advice, and is anyone aware of any kind of standard reference?

 

[Gino]

9" is most likely a small double sided cabinet, converted to a single side. You usually want 4" to 4.5" from the edge of the lamp to the back of the face. Make sure the cabinet (on the inside) is painted all white or silver, because a lotta light is gonna get wasted out the back.

 

[Johnny Best]

6" from lamps to face, is what I always like to use. When using HO lamps you can go a little more.