Adding another light

I am growing plants in two trays in an area 4′ x 5′. I am using a 1000-watt HPS lamp. I’m thinking about adding another 1000-watt lamp to the area. Heat is not a problem since I am using water-cooled lights. Is 100 watts input per square foot too much for the plants? I don’t think so because the sun is brighter than the two lamps combined.
The Kid,
Humboldt County, California

Providing 100 watts of light per square foot (psf) will result in very stocky plants that have a very fast growth rate. In the vegetative stage, this will result in faster leaf, stem and root growth. During flowering the additional light will result in more growth, too. This translates into larger buds and higher total yield.

In order to take advantage of the additional light, the plants must have adequate supplies of nutrients and CO2. Since the plants are building tissue at a faster rate, they are using nutrients more quickly. They must be supplied with enough building blocks in order to use the light for growth.

The higher the light regimen, the more useful an enhanced CO2 level is to increased growth. Using 1500-2000 parts per million will spur growth incredibly. Without it, the growth increase will not be as great, and the lack of enhanced CO2 will be a limiting factor.

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