COMPARISON OF THE EFFECTS OF WATER-COOLED AND AIR-COOLED HIGH PRESSURE SODIUM LAMPS ON LETTUCE GROWTH
The spectral distribution of radiation from the two types of lamps were similar in the photosynthetically active radiation (PAR) wavelength region but the water-cooled lamps produced substantially less radiation in the near infrared (IR) and thermal IR regions. This resulted in an average 0.9 C lower leaf temperature under the water-cooled lamp compared to the air cooled-lamp.
At low (19.1–19.6°C) and moderate (22.5°C) air temperature the water-cooled treatment plants had significantly less mass than the air-cooled plants. At high air temperatures (24.6°C), there was no significant difference in plant mass between lamp treatments. The only conditions for which there was a significant difference in tipburn between lamp treatments was for the low air temperature and the high number of lighted hours. Under those conditions the tipburn levels were significantly lower for the water-cooled treatment.