For stable mass production of vegetable seedlings with good quality, a commercial greenhouse nursery needs a supplemental lighting system that is not affected by light fluctuations under natural solar conditions. Therefore, a practical plant nursery covering a 12 × 24 m area, and using a supplemental lighting system, was developed for the growth of vegetable seedlings. The developed lighting system had 400-W mercury-free, high pressure sodium lamps with reflectors, which produced a red radiation to far-red radiation photon flux (R/FR PF) ratio of 1.1. This is similar to that of solar radiation. And over about 60 μmol m-2 s-1 of PPFD was realized for stable and healthy growth of vegetable seedlings. By using a simulation model of horizontal distribution of PPFD on two cultivation beds (each bed area: 4.6 × 22.6 m) under 100 lamps, it was found that the system had high uniformity of lighting on the two beds. Observed value of illuminance and PPFD and uniformity also satisfied the planned specifications. By repeating a seedling growth experiment using various plants in this greenhouse, it is expected that the practical and effective use of this supplemental lighting system will be possible in rainy seasons or in the late winter period.
A method is described for measuring the wavelength of a laser beam using a pseudo heterodyne converter in order to compare the wavelength with that of a beam from a Zeeman laser. With this method, an oscillating laser at a single frequency is converted to a pseudo heterodyne source by retardation that is modulated by a serrodyne waveform. This method is used in an interferometer made for comparing optical phase. The results from measuring the wavelength of light emitted by a laser diode suggest that this method is better for measuring laser beam wavelengths than conventional methods.
Lighting that uses light emitting diodes (LEDs) is likely to be widely used in the future. However, the effect of the glare from an LED light source on user comfort has not been clarified. To clarify the characteristics of the glare from a white LED light source and its effect on comfort, we conducted the following experiment. A white LED module was used for the light source, and the distance between the subject and light source, and its angle were varied. The subject then gave a value to how comfortable or uncomfortable they felt. When the LED was in the subject's sight and 10 degrees above it, the level of discomfort was assigned the highest and the second highest value respectively. However when the LED was viewed horizontally, the observation distance was large, and the angle was 10 degrees, the glare was assigned a near value. Moreover, when the line of sight was horizontal and the LED was at an angle between 45 and 65 degrees, it tended to produce feeling of discomfort. Furthermore, at an almost near value, compared with the results gained from experiments that used an imitation light source and that investigated the level of discomfort caused by the glare from a white LED light source, the use of an imitation light source appears to be valid.