Have a 250 Watt MH light and must construct a suitable support as the
commercial devices appear quite expensive. How high above phalaenopsis
should the light be?
Hanging from ceiling does not appear to be an option. Hope window will
supply enough red end of spectrum so I do not need in addition a HPS.
Will be lighting a 4x4 area.

(Merrill Speeter) writes:
Have a 250 Watt MH light and must construct a suitable support as the
commercial devices appear quite expensive. How high above phalaenopsis
should the light be?

That depends on your reflector. My vandas are about 30-40cms from mine
in a fairly cold (20C) room. They take about four times as much light
as phals, which should mean that someting like 60-80cms should be
appropriate?

Will be lighting a 4x4 area.

Seems to me you have decided the amount of light each plant will get
already.

Geir

I would guesstimate about 3 feet from the leaf surface. I used to have 1000
watt bulbs hanging 4 feet above Phals. The type of reflector might alter
the distance somewhat. A parabolic reflector disperses the light over a
wider area rather than directing it straight down as other reflectors might
do and this would change the distance somewhat.

It would be ideal if it could be constructed in such a way as to allow you
to move it up or down by as wide a distance as possible. Here are some
other variables to keep in mind. As the bulb ages its output will drop. In
the case of a metal halide this decrease is visually perceptible over the
course of a year or more, especially if you have more than one bulb and
replace them at different intervals. Phals will develop spikes which will
seek the light and may wander into the burn range before you notice. You
may have to move them when they spike if they are under a light a fixed
height. You may also notice in a collection Phals that the leaves of some
wash out in a certain light intensity when the leaves of the plants right
next to them do not. You can use fans to cool the leaves and spikes which
allows the plants to get somewhat closer to the light than without air
movement. Using a highly reflective surface on the walls around the grow
bench will increase the ambient light somewhat and allow you to place the
bulb a bit furthur away if necessary.

It is hard to say how much these variables will matter to your situation.
You might mount it high, like 4 or so feet and then raise or lower the
plants below it as necessary by sitting them up on over turned pots, etc.

"Merrill Speeter" wrote in message
om...
Have a 250 Watt MH light and must construct a suitable support as the
commercial devices appear quite expensive. How high above phalaenopsis
should the light be?
Hanging from ceiling does not appear to be an option. Hope window will
supply enough red end of spectrum so I do not need in addition a HPS.
Will be lighting a 4x4 area.

Merrill,

When I used MH lights I had 400W agrosun bulbs. I tried to keep the bulb
about 4 feet from the plant directly beneath it. Remember that as you get
away from the center the intensity drops.

A 400W bulb 4 feet above the surface would create a primary growing area of
4 x 4 feet. There is an additional foot around the perimeter that would be
find for lower light plants such as paphs.

When I put the bulb on the light track I would move the light a foot closer
to the plants since it was constantly in motion.

When I did this the Phals did quite well.


Gene