light source basics question

Hi all,

I am in the midst of assembling the equipment I need for starting gum
printing and I have a question about my choice of light. I have
decided to go with a 1000 watt metal halide grow lamp, but I have two
questions.

1. What is the optimal distance from the contact frame for this type
of light? Somewhere I got the idea of 40 inches, but that might have
been as a result of a certain amount of falloff and hence, making
sure the hotspot of the light hit the contact frame. In my case, I
plan on doing most of my gum prints smaller than 11 x 17, although I
might do some longer panoramas, up to maybe 24 inches long and about
6-10 inches wide. I'm making a 16 x 30" contact frame, but I might
also make a smaller one too, see how things go.

2. What is a good time range for starting exposure tests? I think it
was in Sandy King's article on unblinking eye that I read exposure
tests where for 5 minutes using this light type. Obviously the time
is going to be related to the distance from the light to the
negative, but I am just trying to establish a baseline for starting.
I am using the chemicals recommended in Livick, so potassium
bichromate.

Thanks all for your help!
Dwayne

-- 
Dwayne Sandall
It is not because things are difficult that we do not dare; it is 
because we do not dare that they are difficult."  -Seneca