Lamp Measurement Methods and Tools

The consistent measurement of low pressure germicidal (UVC) lamps is critical to determine the effectiveness of any given lamp/ballast combination. A basic understanding of simple electricity, the proper equipment and good measurement techniques is all that is necessary to verify and compare lamps.


  • Input Voltage

    • We recommend the use of a variac to control and set the input voltage for all ballast types and lamp measurements.

  • Equipment

    • We recommend an accredited multimeter with the capability to measure  from 5 hertz to 300 Khz.

UVC (254nm) Intensity

  • Set-up

    • Lamps should be measured in a wood box that is painted with a flat black paint to reduce any potential reflected light.

    • Box should be covered with a cloth curtain (also black) to prevent the technician from being exposed to UV  light when making measurements and allow for easy access to the lamps during test set-up.

    • Measurements should be taken in ambient air without a moving air stream. It is generally recommended to make measurements in a stable, controlled and constant air temperature.

      Note: Low pressure lamps are affected by their operating temperature which is affected by room temperature. Special attention should be made to consistently control this factor and we recommend the recording of room temperature to include with any test data.

    • Measurements should be made with the lamp in a horizontial position.

    • Placement of the UV detector is recommended to be one (1) meter above the center of the lamp body and placed equal distance from the two ends (center).

  • Equipment

    • Radiometer. We recommend the use of an accredited radiometer. It is important that this instrument has demonstrated traceability of calibration to a National Laboratory and this calibration is maintained on an annual basis.

    • Detector. For the purpose of uvc lamp measurement we recommend using a detector that “sees” only the uvc region (200-320nm). Many different detectors are available but the elimination of wavelengths above 320nm will make your measurements more consistent and relative.

    • Filters. Narrow wavelength filters that focus closest to the 254nm mercury line are most practical. The use of a quartz neutral density filter is also recommended.

  • Lamp Measurements

    • Record room temperature

    • Ignite lamp and record peak intensity from meter. Generally peak output is used for the purpose of comparing intensity from various lamp/ballasts and determining lamp maintenance over time (depreciation).

    • A temperature probe can be utilized to compare output vs. temperature and determine the optimum lamp temperature for any specific application.

    • It may be desirable to modify these parameters to reflect specific operating conditions.

    • Calculation of “UVC watts”. Many UV equipment and Lamp suppliers refer to “UVC watts” as a measurement of lamp power. For the most part these numbers are derived from a formula based on the work of H.Keitz (1) and may be subject to various assumptions or constants used by that company. First Light supports the work the International Ultraviolet Association to develop industry standards regarding lamp measurement. It is only through consistent measurement and clear standards that the UV industry can gain further acceptance in the marketplace.


(1) Keitz. H.A.E. 1971. “Light Calculations and Measurements, Macmillan and Co. Ltd, London,UK