One trouble with a single light that doesn't move is that some leaves
end up in the shade. Plants off to the side can be shaded by other
plants. Even if you have wide open spaces between plants (a situation
that NEVER lasts for long) there are leaves on the other side of the
plant. I would hope you have painted the walls white or otherwise
provided a way to reflect some indirect light.
A second bulb at a different location in the room would go a long way in
eliminating the shadows. For this reason, I vote for adding a 400 watt
HPS bulb to what you have. The mix of two different kinds of light is
nice too. I have one grow area with that combination. Don't worry,
either 800 or 1000 watts in a room of that size will still have space
for low light plants.

Steve


Doug wrote:
I'm growing in a 6.5 foot by 10 foot room using a single 400 watt metal halide
bulb suspended vertically with no reflector. The light isn't centered but near
an east window where the high light plants are. I have lower light plants as
well that are nearer to the other side of the room. I'm thinking about
increasing the light to either one 1000 watt metal halide or supplementing the
400 watt mh with a 400 watt high pressure sodium light for a total of 800 watts.

I'm growing cats, oncidiums, coryanthes, stanhopeas, phals and a smattering of
other types.

Which do you think would be the best strategy plantwise?

Doug Bolton