A stabilized transfer-standard system for spectral irradiance

A method of measuring the absolute spectral irradiance of quartz-halogen-tungsten lamps is described, based on the known responsivity of a filter radiometer, the components of which are separately characterized. The characterization is described for the wide wavelength range essential for deriving the spectrum of a lamp, from 260 nm to 950 nm. Novel methods of interpolation and measurement are implemented for the spectral responsivity of the filter radiometer. The combined standard uncertainty of spectral irradiance measurements is less than 1.4 parts in 10 2 from 290 nm to 320 nm (ultraviolet B) and 4 parts in 10 3 from 440 nm to 900 nm (visible to near-infrared). As an example, the derived spectral irradiances of two lamps measured at the Helsinki University of Technology (HUT, Finland) are presented and compared with the measurement results of the National Institute of Standards and Technology (NIST, USA) and the Physikalisch-Technische Bundesanstalt (PTB, Germany). The comparisons indicate that the HUT spectral irradiance scale is between those of the NIST and the PTB in the wavelength range 290 nm to 900 nm. The long-term reproducibility of the spectral irradiance measurements is also presented. Over a period of two years, the reproducibility appears to be better than 1 part in 10 2 .

Section: Resultsmentioning

confidence: 99%

Spectral irradiance measurements of tungsten lamps with filter radiometers in the spectral range 290 nm to 900 nm

Kübarsepp¹,

Kärhä²,

Manoocheri³

et al. 2000

“…More worrying is the prospect of alteration of the spectral irradiance characteristics of the lamp during transportation. Such results have occasionally been reported [5] but have not been comprehensively investigated to date.…”

Section: Introductionmentioning

confidence: 92%

“…Since the introduction of the sperm-whale candle by Count Rumford as arguably the first spectral irradiance transfer standard, many alternative light sources have been investigated and used as irradiance standards [1][2][3][4][5][6]. When the scale uncertainties disseminated by national metrology institutes (NMIs) were of the order of several per cent, the limitations of the transferstandard lamps were of lesser importance.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of spectral irradiance transfer standards

Harrison¹,

Woolliams²,

Fox³

2000

The performance of spectral irradiance transfer-standard lamps has long been a concern in the radiometry and photometry communities. The adoption of a modified FEL-type lamp has recently been proposed as the most suitable transfer standard for spectral irradiance measurements. While data have been published on the performance of these lamps when operated continuously and in a laboratory environment, however, little information is available on their performance under typical usage. The results are presented of "real-life" testing of over thirty FEL lamps both pre-selected, according to published procedures, and direct from the manufacturer. When operated vertically all of the lamps tested suffered terminal coil collapse after between 140 h and 250 h burn time. The reproducibility of the FEL lamps after transportation is also investigated.

“…The ability to stabilize using any of the photodiodes provides added flexibility. Stabilization using the UV channel, for example, would provide the most stable transfer standard in the UV-blue region, and since the output of high-power tungsten-halogen lamps is approximately Planckian, much smaller current changes are required to maintain the output in this region than at longer wavelengths, leading to better overall maintenance of calibration [4,5].…”

Section: Introductionmentioning

confidence: 99%

“…The NPL-DSL is a development of our prototype described in [5] and is similar in concept to the OMTec TSS-1000 [4] used in the comparison described elsewhere in these proceedings [6]. Other than differences in the details of the detector arrangement, software, etc., the main difference between the NPL-DSL and the OMTec system is that the NPL-DSL is a fully enclosed system, which has the added benefit of drastically reducing the amount of stray light present within the laboratory, while providing the rigid geometry required for successful detector stabilization.…”

Section: Introductionmentioning

confidence: 99%

The NPL detector-stabilized irradiance source

Windsor¹,

Harrison²,

Fox³

2000

The design of a new detector-stabilized spectral irradiance source is presented, together with an evaluation of its performance. This new source consists of a tungsten-halogen lamp that is current-controlled using feedback from an array of filtered photodiodes. The bandpass and central wavelength of these filtered detectors may be selected specifically to meet the required application of the source. The lamp is fully enclosed (except for the exit aperture) in an air-cooled, light-tight housing that minimizes unwanted light pollution. The lamp current is stabilized using feedback from one photodiode; the recording of the non-stabilization channels allows a real-time check on the effective colour temperature of the lamp, and provides an instant diagnosis of the state of calibration of the lamp. The calibration data for each lamp (in its associated housing) are stored on a microchip within the lamp housing, which allows the lamp to be transported independently of its associated control electronics for calibration purposes. The performance of the lamp indicates ageing rates of better than 2 10 -5 h -1 , across the ultraviolet-A (UV-A) and visible spectral regions.