Every CCT, CRI, and SPD figure covered in our CRI/CCT/SPD explainer ultimately comes from the same source instrument: a spectroradiometer. But this covers genuinely different designs — portable handheld units, sphere-integrated systems, and scientific-grade scanning instruments — with real differences in what each can actually measure accurately.
What a Spectroradiometer Actually Does
A spectroradiometer measures optical power as a function of wavelength — the raw spectral power distribution curve every colorimetric figure is derived from. This differs fundamentally from a filtered tristimulus colorimeter, since genuine spectral data doesn't carry the approximation error filtered instruments can introduce, particularly for unusual or narrowband spectra.
CCD Array vs Scanning Designs
Array (CCD) spectroradiometers spread light across a diffraction grating onto a linear CCD sensor, capturing the entire spectrum in a single exposure — dramatically faster than scanning designs, which is why CCD instruments dominate production-line and routine LED testing.
Scanning spectroradiometers use a mechanically rotating grating to sequentially measure narrow wavelength bands, slower but achieving excellent stray-light rejection in well-engineered instruments, which is why they still appear in scientific-grade reference calibration work.
Standalone Instrument vs Sphere-Integrated System
A spectroradiometer is a component, not a complete system on its own. Standalone, it measures spectral irradiance directly from a source. Integrated with an integrating sphere — the combination covered in our integrating sphere vs goniophotometer guide — it becomes the spectral engine for a complete photometric system, producing the full set of LM-79-required data from a single test. Most LED and luminaire labs need this sphere-integrated configuration for routine product testing.
Key Specifications That Actually Matter
| Specification | Why it matters |
|---|---|
| Spectral wavelength accuracy | Directly affects CCT, CRI, and chromaticity accuracy |
| Stray light rejection | Poor performance inflates apparent flux at wavelengths not actually emitted |
| Integration time range | Wider range supports both dim and bright sources without saturating |
| Detector cooling | Thermoelectric cooling reduces noise for low-light precision work |
| Spectral range | ~380–780nm suffices for most lighting; UV/IR extension matters for specialty applications |
For routine LED and luminaire compliance testing, a CCD spectroradiometer integrated with an appropriately sized sphere — such as the LISUN LMS-9000C — covers the great majority of LM-79 requirements. Scientific-grade cooled-detector instruments are worth the additional cost for research or unusually low-light sources.
Portable Spectroradiometers
A separate category — compact, handheld spectroradiometers — trades accuracy and spectral range for field portability, measuring CCT, CRI, and illuminance directly at an installed luminaire's location. Well suited to field verification and quality spot-checks, but not the right tool for formal LM-79 compliance reporting.