Please note that this review was written in 2010. Visit the current grow lights page for the most recent information on marijuana grow lights.
Sulphur Plasma Grow Light Systems (MPS)
Sulphur Plasma Grow lights are the newest grow light technology on the market that I have heard of. I have done a little bit of research on these and the plasma lights are extremely expensive right now and I don't feel very confident about the light spectrum they put out. I looked up a unit at chameleongrowsystems.com and saw that it cost $1,000.00 for a 250 watt Plasma light unit.
In addition to the prohibitive costs of plasma lights right now, there seems to be a problem with the light spectrum. For marijuana, you have chlorophyll a and b which is what absorbs the light and turns it into energy. For chlorophyll a, optimum light absorption occurs at 430nm and 662 nm in the light spectrum. For chlorophyll b, the optimum part of the light spectrum is at 453 and 642 nm.
This graph shows the optimal spectrum for light absorption for chlorophyll a and b(from wikipedia):
Optimal Light Absorption by Plants
Here are two graphs showing the light spectrum produced by Sulphur Plasma Lights. In the second picture, the colored in part of the picture is the spectrum of light put out by the sun. The jagged white line shows the light spectrum put out by the plasma lights.
Light Spectrum produced by Sulphur Plasma Lights
Graph One (from Wikipedia article on Sulfur Plasma Lamps)
Graph Two (by Chameleon Grow Systems)
From the pictures, it appears that the most light is put out in the 500-600 nm range by plasma lights, which isn't very useful for plant growth. In addition, marijuana plants need light in the 430-453nm range in order to have proper vegetative growth, and it looks like the light output by the plasma lights actually dips extremely low right in that crucial range (according to the Chameleon grow system graph). It also looks like the light spectrum put out by the plasma lights starts dipping in the range needed for flowering growth as well.
Therefore, even if the plasma lights are extremely efficient and powerful, it appears that they are just producing a spectrum of light that isn't going to be very useful for plants growth.
For me, I'm definitely waiting until the price comes way down and there are at least some sort of definitive studies come out showing that they actually work before I would consider buying one.