Lighting Research & Technology

The visual performance of Chinese adults, 20 to 30 years of age, is evaluated as a part of a study determining illumination standards intended for use in The People's Republic of China. Spatial acuity was measured with Landolt rings as a function of visual angle, contrast and illuminance. The influence of these variables on visual performance is described by a mathematical model. The results are compared with the standard RCS visual performance curve recommended by the CIE.

Measurements of daylight at hourly intervals were made during seven periods of several weeks each between May 1978 and July 1979. Illuminance was recorded externally, on horizontal and vertical surfaces, and internally, within model rooms. It was found that the ratio of internal to external illuminance varied considerably, even under heavily clouded skies.

International recommendations on surface colours for traffic signs and on traffic lights have existed for a long time, but at the present time there are no recommendations for colours of transilluminated traffic signs. This investigation shows that colours of transilluminated traffic signs by day and night could be in agreement with the requirements of CIE Publ. 39, but for white colours by night the white chromaticity region of CIE Publ. 2 would be more appropriate. For the illumination of transilluminated traffic signs fluorescent lamps with light colour 15 "daylight de luxe" and 19 "daylight 5000 de luxe" give the best results.

An improved technology for the production of fluorescent lamps is described. Coated glass tubes after passing through a baking lehr are loaded, while still hot, onto a single machine equipped with multi-function heads. The machine completes the cycle of sealing, exhausting, cathode conversion, argon filling and tip-off. Mercury is then dosed in the sealed lamp by the high frequency heating of a special cathode shield coated on one side with a mercury releasing alloy and on the other with a getter which acts during the lamp life to absorb impurities released. The optimisation of the argon flushing process is discussed using a mathematical model. Advantages offered by the new process are described.

A simple method is proposed to characterize the shape of the temperature profile of the arc in high-pressure discharge lamps. The method is based on the balancing of natural convection by external magnetic forces in the horizontal burning position. Experimental results are given for some well-known lamp systems including the mercury arc, the tin halide arc and the sodium-thallium-indium iodide arc, under various conditions. The results are in accordance with the trends observed in practice. Results are also given for rare-earth iodide arcs. In these systems arc motions occur under certain conditions. The nature of these phenomena is discussed.

The methods used for calculating economic lamp lives by Strange and Prais are examined. It is concluded that neither is completely sound and an alternative formula is developed. The results although differing in detail from those of Strange are broadly in accordance with his findings. The longer economic lives suggested by Prais cannot be justified. No support for any general change in the rated life of electric lamps comes from these figures, but it is suggested that it might be worth offering a long life lamp of relatively low wattage for domestic use. For commercial consumers no single lamp life is likely to cover the range of situations to be found in practice.

An inexpensive portable instrument is described for the paired comparison observation of direct discomfort glare in interior lighting installations. It is useful for field tests where it complements glare assessment by verbal statements.