Lighting Research & Technology

Some of the visual objectives for which different levels of illumination are, or may be, recommended are considered and mention is made of the kind of experimental data available for the development of illumination prescription systems. Such experimental data underlie the recent Russian and American recommendations which are discussed briefly. It is taken as always desirable that lighting installations in regularly occupied interiors should provide sufficient illumination to create an agreeable environmental or ambient luminance, irrespective of the specific visual tasks occupants may be required to do: hence, what illumination may be recommended reasonably for securing this basic amenity luminance in places of work is considered. The existing British analytic method of finding basic values of illumination for various definite visual tasks is examined and a modification is proposed to simplify practical use of the method. In view of this, a new definition of the visual performance criterion is proposed and a general, although moderate, increase in recommended levels of illumination is likely to be consistent with this.

During the past twenty-five years there has been spectacular progress in the development of electric lamps. While this applies mainly to discharge sources, much work has gone into incandescent lamps, which, despite their relatively low luminous efficiency, have not diminished in importance. An entirely new method of converting electrical energy into light by electroluminescence has been evolved, which, however, has not fulfilled its early promise. On the other hand, at a time when progress in conventional discharge sources might reasonably be expected to have levelled off, new ideas have evolved and substantial improvements have been made. The paper discusses the more important developments and trends in the field of electric lamps.

Some of the terms used in lighting design calculations for the components of flux in an interior and their ratios are described. Suggestions are made for some new terms and symbols, and for a more practical meaning for ‘light output ratio’.