Photometric Measurement Systems
Complete Photometric Characterisation from Goniophotometry to Spectroradiometry
Fully characterising how a light source performs means measuring several distinct things: the spectral power distribution and colour properties, the total luminous flux it emits, and how that light intensity distributes across different angles — three related but genuinely separate measurements, each requiring its own instrument geometry. LISUN's LSG / LMS / IS Series covers the complete measurement chain: goniophotometers and goniospectroradiometers for intensity distribution, integrating spheres from tabletop to 3-metre diameter for total flux, and CCD spectroradiometers for spectral and colorimetric measurement.
Goniophotometers measure how luminous intensity varies with angle around a light source or luminaire, essential for luminaire design and for standards like IES LM-79 and EN13032-1 that require full intensity distribution data, not just a single total-output number. The range spans from CIE Class A precision instruments with angle accuracy down to 0.01° — suited to accredited laboratory work — through to more compact rotating-mirror and combined-format models for general LM-79/EN13032-1 testing where the highest angular precision isn't the deciding requirement.
Integrating spheres measure total luminous flux by capturing essentially all the light a source emits, with sphere diameter scaling to match the source being measured — larger sources and higher flux outputs generally call for larger spheres to maintain measurement accuracy. CCD spectroradiometers, meanwhile, measure the spectral power distribution itself, the basis for colour rendering index, correlated colour temperature, and other colorimetric parameters buyers and specifiers increasingly require documented. Complete LM-79 compliant integrating sphere spectroradiometer systems combine sphere and spectroradiometer into a single turnkey solution, appropriate where a lab needs full LED and luminaire photometric testing capability without assembling and validating the individual components separately.
Frequently Asked Questions
Why do intensity distribution, total flux, and spectral measurement each need a different instrument?
Each measurement captures a fundamentally different aspect of a light source's output: a goniophotometer maps how intensity varies by angle (important for luminaire beam design and glare), an integrating sphere sums total emitted flux regardless of direction (the basis for efficacy and lumen output specifications), and a spectroradiometer measures the wavelength-by-wavelength spectral content (the basis for colour metrics). No single instrument geometry can capture all three accurately.
What determines whether a smaller or larger integrating sphere is needed for a given measurement?
Sphere size affects both the physical light source size that fits inside without excessive self-absorption error and the accuracy achievable at a given flux level — a source that's large relative to the sphere, or a source that occupies too much of the sphere's internal surface area, introduces measurement error. Matching sphere diameter to the source's physical size and expected flux output keeps measurement accuracy within specification.
What does a complete LM-79 compliant system add over assembling individual instruments separately?
A complete system combines a validated integrating sphere and spectroradiometer configuration already characterised and calibrated together as a unit, reducing the setup, calibration, and validation work a lab would otherwise need to do when combining individually sourced components — relevant for a lab standing up new LED and luminaire photometric testing capability from scratch.
