Addition of CaBr₂ intensifies red light, which is favored by plants.

Calcium bromide can be added to the sulfur filling in a sulfur lamp to increase the emission of red light for enhanced growth of plants. Red light is more efficacious for plant growth than is visible light at shorter wavelengths. The addition of CaBr₂ increases the emission at wavelengths in the vicinity of 625 nm, where the quantum efficiency for photosynthesis is close to 1.

A sulfur lamp is an electrodeless lamp that includes an evacuated quartz bulb partly backfilled with argon and with a little sulfur, plus a source of microwave power for exciting a plasma within the bulb. A sulfur lamp is very efficient for visible lighting. An attempt to increase the emission of red light by increasing the sulfur content would result in an excessive reduction in the emission of blue light. Alternatively, following a common practice in the lighting industry, one could attempt to increase the red emission by adding such metal halides as sodium iodide: in the presence of the lamp plasma, the metal atoms in most such additives become excited and ionized and they radiate in the desired spectral region, but they also emit unwanted infrared line radiation, with a consequent reduction in efficacy for growth of plants.

The Measured Spectrum of a Sulfur/Calcium Bromide Lamp is plotted along with the spectrum of a similar sulfur lamp without calcium bromide. The prominent spectral peak of the S/CaBr₂ lamp lies at the wavelength region of highest quantum efficiency for photosynthesis in plants.

This work was done by Youngzhang Leng and Donald A. MacLennan of Fusion Lighting, Inc., for Kennedy Space Center.

In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to: Donald A. MacLennan, Fusion Lighting, 7524 Standish Place, Rockville, MD 20855; (301) 284-7200.

Refer to KSC-11970, volume and number of this NASA Tech Briefs issue, and the page number