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Spectral tri-function automated reference reflectometer (STARR)

STARR performs directional-hemispherical, specular, and bidirectional reflectance measurements of spectrally neutral, non-fluorescent samples at room temperature. It currently serves as the national reference instrument for directional-hemispherical reflectance measurements. The national reference instrument for specular and bidirectional reflectance measurements is the Robotic Optical Scattering Instrument (ROSI).

STARR uses a lamp-based, quasi-monochromatic system for illumination of the sample and broadband detection for the reflected radiation. Directional-hemispherical measurements are acquired using an integrating sphere and require comparison to a calibrated standard, pressed polytetrafluoroethylene (PTFE). All specular and bidirectional measurements are collected in-plane, meaning the sample normal, illumination axis, and receiver axis are in the same plane.


Conditions for reflectance measurements using STARR

  Bi-directional Directional-hemispherical
  Specular Diffuse  
Illumination Angle 0° to +80° 0° to +80° 6° (specular included) 0° (specular excluded)
Viewing Angle 0° to +80° 0° to +80° Hemisphere
Sampling Aperture 17 mm 17 mm 25 mm
Wavelength 250 mm to 2500 nm 250 nm to 1100 nm 250 nm to 2500 nm
Bandwidth 14 mm 14 nm 14 nm
Polarization 0° to 90° 0° to 90° Slight
Sample Size 50 mm to 300 mm 50 mm to 300 mm 50 mm to 300 mm
Quantity Reflectance BRDF, Reflectance factor Reflectance factor
Technique Absolute Absolute Relative to PTFE
Range 0.001 to 1 0.001 to 1 0.001 to 1
Uncertainty (k=2) 0.1% to 0.2% 0.15% to 0.6% 0.15% to 0.6%


Created October 21, 2009, Updated January 3, 2020