Fluorescent Lights - Part Two
By Jerry Meislik
This is part two of a continuing experiment comparing LED grow lights vs. a four tube fluorescent light setup. With the recent advent of LED plant lighting I was very interested in seeing how LED lights would work growing bonsai indoors. Part one of the experiment can be viewed by clicking here.
LED lights have the advantages of having low energy requirements and yet high efficiency in producing light that is tailored to the frequencies needed by plants. Excess energy is not wasted on producing heat or in producing light frequencies not used efficiently by plants, such as green light.
In Part Two I planted 30 pots containing seedlings of Ficus virens 'Thai' in 100% red lava particles of about 1/8"-3/8" size on May 15, 2007. The seedlings were 4 months of age and all were removed from their nursery containers and planted into the red lava. Plants were placed 3-5 per container and varied so that each container had some smaller and some larger seedlings. The pots were then randomly placed under either the LED or fluorescent lights to ensure that similar sized plants were placed under each light setup. Fifteen pots were under each light setup. The pots were watered immediately and placed under either a fluorescent light housing four 24 inch bulbs, composed of two normal daylight and two plant lights, or under an LED grow bar. See Part One of this article for more details.
The fluorescent lights were suspended 6 inches above the plants tops while the LED bar was located 18-20 inches above the plants tops as per manufacturer recommendation. The plants were watered as needed with reverse osmosis water containing a dilute fertilizer mixture. Experimental conditions were otherwise the same as in part one. The only differences in Part Two were the soil, the distance of the LED from the plants and the type of plants.
The experiment was terminated on August 6th, 2007; a nearly three month trial.
Plants were observed for general overall vigor, leaf color, leaf thickness, stem thickness as well as height of the plants. Photo one shows the tray of fluorescent grown seedlings. Note the red color of many of the leaves and the overall leaf density. The plants growing under the fluorescent lights looked very vigorous with good leaf substance, good stem thickness, good leaf density and color. The plants overall were larger than in the LED group.
Photo two shows the plants grown under the LED light bar. Although the plants looked reasonably vigorous the overall leaf substance, stem thickness, leaf color, and leaf density was not as good as the plants under the fluorescent light. Overall the plants were generally smaller that under the fluorescents.
Photo three shows two pots from the fluorescent and two from the LED on the right. These were the smallest plants from each tray. Again the fluorescent pots on the left showed better growth.
Conclusions and comments:
In this experiment the fluorescent four tube light setup proved superior to the LED light bar. Plants were more vigorous, had more leaves, leaf thickness and stem thickness were better underneath the fluorescent lights.
On balance the LED light bar was more efficient in electric use, produced much less heat, and required less water.
Under my experimental conditions with one variety of Ficus tree fluorescent lights proved superior to the LED light bar. As the cost of LED grow lights comes down they will they will find more use in environments requiring low electrical consumption, and low energy costs. I anticipate further improvements in LED technology will make them even more competitive.