Spectroradiometer is a basic measurement instrument which measures quantities like luminous flux, luminous intensity, color temperature, color rending index etc. In comparison to the traditional mechanical scanning spectroradiometer, the High Accuracy Array Spectroradiometer (HAAS) can measure the spectra in milliseconds with high accuracy. Due to the special properties of LEDs, the transient (pulse) measurement is often required, and the spatial colorimetric non-uniformity test also needs high speed for efficiency. All these measurements can be accomplished by HAAS.
HAAS in International Standards
The HAAS has attached more and more importance in national and international standards for the measurement of LED products, such as IS 10106, CIE S025, IES LM-79. The content on array spectroradiometer has also been added in the newly revised IES LM-58 “Spectroradiometric Measurement Methods for Light Sources”. Also, the CIE TC2-51 is working on the standardization of the chararcterization of array spectraoradiometers.
HAAS and Characteristics
Generally, HAAS adopts high quality gratings and sencitific-grad array detectors. But it should be noted that not every back-illuminated CCD spectroradiometer can be a HAAS. Compared with normal high-speed spectroradiometers, the performance of a HAAS in the aspect of spectral resolution, wavelength accuracy, stray light, linear dynamic range and stability have been highly enhanced.
The most important specifications of a HAAS are dynamic range and stray light.
- Dynamic range: The dynamic range is defined as the full scale signal divided by the minimum resolvable signal. For spectrometers the minimum resolvable signal can be defined as the standard deviation of the dark signal. The stability of the spectroradiometer increases with wider linear dynamic range. The linear dynamic range is mainly limited by the photoelectricity sensors.
- Stray light: Stray light is the radiation at wavelengths other than the one being measured enters the detector element, and the corresponding spectral power is over estimated. Stray light rejection is key for blue part measurement because the calibration source (illuminant A) has abundant red part spectrum and the detector is much more sensitive to red light.
- Pixel resolution: As each pixel of the array detector of a HAAS corresponds to a position in the wavelength scale. The wavelength difference between one pixel and the next is the pixel resolution. This is not the same as the optical resolution which is generally larger.
- Optical resolution in the strictest sense is the ability to separate (resolve) two wavelengths from one another. The specification is done by measuring the Full Width Half Maximum (FWHM) of various spectral peaks of a line source such as Hg and Ar lamps.
The FWHM is used to characterize the optical resolution of a HAAS
EVERFINE HAAS-2000/3000 and test applications
With continuous progress in research and technology innovation, EVERFINE has successfully improved the optical matching of the system to make it more perfect, and the performance of stray light rejection and linear dynamic range have also been enhanced remarkably. It is a breakthrough to use patent Bandpass-filter Wheel Correcting Technique (BWCT) in multi-channel
spectroradiometers to reduce stray light and use Spectrometer & Broadband-radiometer/photometer Combined Technique (SBCT) to widen the linear dynamic range, together with the other technologies, such as the modified NIST stray light correction technology, the precise array detector driving technology and complex variable matrix technology. HAAS-2000/3000 now has extreme low stray light level as 5.00E-05. The linear range has been enlarged up to 0.3% in 8 orders of magnitude from the original 1% in 3 orders. It is an ideal instrument for both research and production.
Over twenty years of continuous design refinements, software developments, and practical day to day usage has enabled EVERFINE to offer high performance HAAS spectroradiometers as the standard in the LED lighting industry. With truly unequaled speed, accuracy and functionality, EVERFINE’s are the most sophisticated one available. Every major authoritative laboratory and lamp manufacture has acquired HAAS such as BACL,Cree, GE, OSRAM, Philips, and Siemens while in India it is TUV, Havells, Samudra, Fiem, HPL, and NTL among others.