“The rating of incandescent lamps and their accessories”

I wish to confine most of my remarks to the subject of glare. There is one cause of . glare in lamps which does not appear to have been discussed very much, and which is produced by reflection from certain regions of the glass bulb. I do not refer to the ordinary thin reflection of the filament which one can generally observe, but to the caustic effect or partial flashing-over of part of the bulb, so that light is collected and reflected to the eye from a comparatively large area. When the bulb is viewed from certain directions, this partial flashing-over gives rise to bands of brightness in space, and these bands must necessarily cause a diminution of illumination in other directions. The net result is to give a peaked curve of candle-power distribution.