Photometric standard lamps having a low luminous intensity and a colour temperature greater than about 2700 K have undesirably short lives. A new standard lamp which is being developed at NPL in collaboration with the GEC Hirst Research Centre should overcome this problem. It consists of a vertical ribbon filament lamp with the area of the lamp wall in front of the filament cut off from the rest of the lamp by an internal boxed screen. At the centre of this screen is a small circular aperture which limits the effective area of the source. The luminous intensity of the lamp is equal to the area of the aperture multiplied by the luminance of the filament. Since a ribbon filament lamp has a reasonable life when run at the colour temperature of Standard Illuminant "A" and since the aperture can be made small, an intensity of the order of a few candelas is practicable yet with a good life. In addition the light is virtually unpolarized. The possibility is also envisaged of using alternative and quicker methods of accurately calibrating such lamps and of making lamps with vertical slit apertures for use with spectroradiometers.