To achieve better efficiency in the response of plants to fluorescent light, special tubes have been designed which emit proportionately more blue and red wavelengths of light. The loss in this portion of the spectrum, even though it is slightly efficient has not been compensated by enough increase in the blue-red portion of the spectrum to result in increased plant growth. Critical experiments show that maximum growth of most plants under cool white fluorescent lights will be equivalent to or better than that obtained under the blue-red phosphors. Some of the names of these special tubes are Grolux, Plant-Gro, Plant Light, Vita Light and Optima. The higher cost of these fluorescent tubes may be justified on experimental or aesthetic grounds but is hardly warranted on the basis of plant growth.
Intensity also affects the growth of plants.
The brighter the light, the more energy the plant receives. To determine how much light a plant will require, consider where and how it grows best in its natural environment. Most vegetable and many mature flowering plants that grow in full sunlight need a high light intensity of 25 to 30 lamp watts per square foot. Mature leafy house plants and growing seedlings will do well with 15 to 20 watts per square foot. Many plants are photoperiodic.