Different light sources

I’m growing four plants, two in each 8-inch pot under a 150-watt high pressure sodium lamp that shields UV light. They are now two weeks old and are growing a treat!
I live in a part of the UK that’s fairly cloudy. However when we do get a glorious sunny day, I place my plants in the window to get as much of the natural light spectrum as possible. When it gets dark or cloudy, they go back on the lamps.

I just read an article that says moving from the one light source (sun) to the other (lamps) could kill the plants as they need to stick with what they have become used to. Can you help?


I recently transplanted my plants from fluorescent lights to a 1000-watt high pressure sodium (HPS) light. They are growing in an air-conditioned two foot by six foot closet with the door open and a fan blowing. The edges on the upper leaves of my plants are curling up in a cylindrical fashion, but are otherwise fine. What am I doing wrong?

First Time Indoor Grower
Pullman, Michigan

The author of the article referred to in the first question above could have been writing about several problems that arise with exposing plants to different light sources. Leaves that have been grown indoors usually have not been exposed to much UV light. This is the same spectrum that causes skin to tan. When the plants are taken outside and exposed to high levels of UV light, they may dry out from the exposure.

Another possibility is a problem that the plants face if they are placed in the window only once or twice weekly. If the plants are used to a certain intensity of light, and then are exposed to a much higher intensity, the leaves will suffer and may die. If the sun through your window is very bright, it may be much more than what the plants are used to. The leaves will get a sunburn, resulting in a major setback to the plants.

If the plants are under the lamp and sun on a more or less daily basis so the leaves have grown with the sun, then the plants will appreciate the extra intensity. Note that window glass shields against UV light, so those plants will still not be acclimated to true outdoor light.

When the plants were placed under the 1000-watt HPS after being grown under fluorescents, they had a problem handling the intensity of the new light. Although these leaves are damaged, the new growth ? grown under the high intensity light ? will not have this problem.

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