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PARISS: Radiometric calibration light source

SYLPH™: Hyperspectral Radiometric Calibration Light Source


 A NIST traceable light source to enable radiometric correction of a spectrometer output. Primarily for use with any microscope based spectrometer system

“SYLPH™” Standard Yield Lamp for Photonic Calibration

Ensures that a spectrometer reports the  power (W/cm^2/nm) of a spectral emitter independent of diffraction gratings and camera QE, optical coatings or lens characteristics

How The SYLPH Hyperspectral Radiometric Calibration Light Source Works

"SYLPH" radiometric calibration assembly

The Sylph radiometric calibration system setup (not to scale).  The illumination head is placed facing the microscope objective

Why Calibrating A Hyperspectral Spectrometer Is Necessary:

Instrument to instrument variability: Unless they have been “standardized” all spectrometers will characterize a reference emission spectrum differently. This is a function of many issues including variations in detector efficiency, bandpass and various system optics

Uncertainties in wavelength ratios: If a sample spectrum covers an extended spectral range, wavelength ratios may vary between instruments due to instrumental component variables. If measuring accurate wavelength ratios is necessary then the data delivered by an instrument needs to be “normalized” to a standard.

Without correction, data will be highly reproducible, yet wavelength ratios will be “precisely inaccurate.” The main wavelength dependent culprits include:

  • The quantum efficiency (QE) of the spectrum detector such as a CCD or CMOS camera or photomultiplier tube (PMT)
  • The wavelength versus efficiency profile of a diffraction grating or prism
  • Variations between electronic bandpass filters such as Acousto Optic Tunable Filters (AOTF), Liquid Crystal Tunable Filters (LCTF) or interferometers.
  • Optical coatings, lenses, mirrors, filters, polarizers and any other optic that is located between the sample and the detector
  • Aliasing when the system fails to accurately reconstruct an analog spectrum into a digital format.

The impact of all these influences are eliminated when a spectrum is acquired in %transmission, absorption, or %reflection.  In these cases, the sample spectrum is divided by a spectrum of the illumination source that has also passed through the same system.

However, in emission spectroscopy including LED, OLED photo-luminescance fluorescence, and Raman there is no illuminant spectrum to divide by. Therefore, in order to accurately reconstruct wavelength ratio intensities, it is necessary to apply a correction factor at each wavelength.

The NIST Certified Radiometric Calibration Solution

The accepted way to normalize any spectrometer is to acquire a spectrum of NIST certified characteristics.  For wavelength accuracy use an absolute light source such as the MIDL Hg/Ar emission lamp.  For wavelength versus intensity use a NIST certified emission lamp such as the “SYLPH” radiometric calibration light source.

The SYLPH radiometrically calibrated light source delivers a stable, NIST-certified spectrum of known characteristics. This provides a spectral microscope or spectral confocal system with a certified traceable “reference emission.”  

To standardize a system determine a correction curve by acquiring a spectrum of the SYLPH  lamp and compare it to the spectrum described in the certificate. After applying the correction curve the spectrometer will reconstruct the spectrum of the SYLPH lamp and accurately reconstruct the spectrum of any other sample.

Once this correction factor has been incorporated in the data processing software it should be applied to all future acquisitions.

Bottom line:  All radiometrically calibrated instruments will accurately reproduce the same reference spectrum.  Once an instrument has been radiometrically corrected all spectra acquired on that instrument can be compared with those acquired on other radiometrically calibrated instrument.

Radiometrically Calibrate These Instruments

Microscope mounted monochromators, spectrometers, imaging spectrometers, spectral confocal instruments, AOTF and LCTF systems, and interferometers.

NIST certified radiometric calibration light source spectrum

NIST Certified radiometric power spectrum as a function of wavelength

Spectrometer rendition of a NIST certified light source before radiometric correction

Relative spectrometer spectrum of the NIST lamp before correction

Following radiometric "correction" the spectrometer and NIST plots are the same

After radiometric calibration a correction an instrument will acquire an identical spectrum to the NIST certification

Without radiometric correction a spectrum will be precisely inaccurate!

SYLPH Hyperspectral Radiometric Calibration System Specifications

Wavelength range:
Warm-up time:
Bulb power:
Source lifetime:
Calibrated for:
Stability of optical output:
Drift of optical output:
Operating temperature:
Power Consumption:

Tungsten halogen
360-2400 nm
10 minutes at 23deg ambient
4.75 W (nom)
10,000 hrs (typical)
Absolute irradiance (µW/cm2/nm)
0.15% peak-to-peak
<0.3% per hour
5 °C – 35 °C
5-95% without condensation at 40 °C
up to 15 W

Darkfield hyperspectral nanoparticle characterization 

How PARISS hyperspectral imaging microscopy works

PARISS hyperspectral imaging microscopy modes of operation

*Assuming all instruments as set to run with the same spectral bandpass

All PARISS Hyperspectral systems are custom configured to meet the needs of an application.
The above configuration is for
guidance only. Specifications can and do change without notice.

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