Working Standard Lamp

(photometric lamp), an electric light source that produces some given light intensity. It is used for photometric and spectral measurements in the ultraviolet (UV), visible, and near infrared (IR) regions of the spectrum.

Specialized incandescent working standard lamps are used to reproduce photometric units and to measure luminous intensity and luminous flux. Those used in measurements of luminous intensity emit light with a nominal luminous intensity from 5 to 1,500 candelas; those used in measurements of luminous flux emit light with ratings from 10 to 3,500 lumens. Some incandescent working standard lamps may be designed with straight filaments operating in a vacuum; they have a color temperature of 2360°K or higher. More powerful, gas-filled lamps with filaments in the form of a spiral have color temperatures from 2800° to 2854°K.

Depending on the accuracy required for the production of photometric units, working standard lamps are classified as standard lamps with a root-mean-square (rms) deviation of the measurement relative to the mean value of less than 3 percent and as first-degree, second-degree, and third-degree model lamps with rms deviations of 0.4, 0.6, and 1 percent, respectively. Some incandescent working standard lamps are used as secondary standards.

The reproduction of instantaneous (peak) values of luminous intensity in a pulse and values of luminous pulse emittance is posible with the use of pulse gas-discharge light sources. The nominal values of peak luminous intensity in spherical IShO-1 and tubular IPO-75 lamps produced in the USSR are 3 × 10⁵ and 3 × 10⁶ candelas, respectively; the values of luminous pulse emittance are 0.9 and 300 candela-seconds, respectively. The relative rms deviation of the peak luminous intensity in pulses for these lamps does not exceed 1.7 percent.

Values for luminance and color temperatures in the range from 800° to 3000°K in the UV, visible, and near-IR regions are reproduced by various grades of working standard lamps with incandescent elements in the form of a thread, ribbon, or glowing cavity.

Spectral gas-discharge lamps with line spectra are used for the reproduction of wavelengths in the calibration of spectral instruments; the resonance emission of such lamps is concentrated in very narrow spectral ranges. The reproduction of the intensity distribution of UV emission in absolute units is accomplished by means of a gas-discharge mercury-vapor lamp used as a standard.