Leaning from the light

I have some clones that have been under fluorescent lighting in a Phototron. I recently placed the clones under a 430-watt HPS lamp.
The plants look very healthy, but they are leaning away from the light. What gives?

Sela at the Tub,

The plants are reacting to the increased light intensity by moving away from it. The leaves grown by the plant were designed to utilize fluorescent light most efficiently. Had the leaves grown under HPS lamps they would have been modified to deal with the increased intensity. Without these protections the plant is doing the next best thing: moving away from the light.

The plant will soon start replacing the old leaves with new ones that are more suited to the existing conditions.

You can help the plants by increasing their distance from the lamp so the intensity of the light lessens as it spreads over a wider area. As new growth appears the light can be lowered a bit. An unprotected 400-watt lamp should be placed two to three feet above the canopy to allow the heat to rise without affecting the plant tops. Air and water cooled lamps can be placed closer to the plants because the heat they emit is controlled.

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