Plant growth with new fluorescent lamps

Summary

Tomato seedlings were grown under seven kinds of fluorescent lamps, including two that are commercially available, and five experimental lamps. Detailed descriptions and spectral emission curves for these lamps are presented.

The 78/22 lamp, which emitted most of its energy above 500 mμ, more than ten percent above 700 mμ, and had a sharp peak output at 660 mμ, generally produced superior fresh and dry weight yields. This effect may be due primarily to the high peak of energy emitted at approximately 660 mμ, combined with a considerable emission in the far-red, which in turn may be related to the red ↔ far-red reversibility phenomeon.

The Com I lamp, which lacked the sharp peak output at 660 mμ and emitted more energy in the blue than the 78/22 lamp, was generally second only to the latter in promoting plant growth. A high moisture content was found in plants under this lamp in some experiments.

The IRIII lamp had the sharp peak output at 660 mμ but greater output in the blue than the 78/22 lamp. The 282 lamp output was similar to the 78/22 but lacked the high peak. Both of these lamps generally gave improved results over those produced by commercial Gro-Lux, Warm-white, and FLAT lamps. This was attributed to the greater percentage of red and far-red energy emission by the former two lamps. The yields with the FLAT lamp were consistently lowest of all. This has been attributed to the high percentage of emitted energy in the blue and green portions of the spectrum.

Both length of the test period (13 days versus 26 days) and light intensity (550 μw/cm² versus 1100 μw/cm²) may be important factors in determining which composition of spectral energy emission produces the greatest yields. Under low intensity and short test period the Com I light produced highest fresh- and dry-weight yields, but under high intensity and longer growth period the 78/22 lamp gave greatest yields. This effect may be due to inhibition of leaf expansion by red light in the early stages of growth.

The experiments demonstrate that it is possible to develop a fluorescent lamp for plant growth that combines the desirable characteristics of both incandescent and fluorescent light. This work also shows that the tomato plant in the seedling stage grows best under an artificial light source with a high percentage of energy emission in the red, a considerable amount in the far-red, and a very small amount in the blue part of the spectrum.