Introduction to Colour Temperature Measurement

Colour temperature is a fundamental parameter in photometry and radiometry, defining the chromaticity of a light source by comparing it to the emission spectrum of an ideal black-body radiator. Measured in Kelvin (K), it quantifies the perceived warmth or coolness of light, influencing applications ranging from architectural lighting to medical device validation. Accurate measurement requires specialized instrumentation, such as spectroradiometers or dedicated colour temperature meters, which capture spectral power distribution (SPD) and derive correlated colour temperature (CCT).

This article examines the technical principles of colour temperature measurement, industry applications, and the role of high-precision instruments like the LISUN LMS-6000 series in ensuring compliance with international standards.

Fundamentals of Colour Temperature and Its Measurement

Black-Body Radiation and the Planckian Locus

The concept of colour temperature originates from Planck’s law, which describes the spectral radiance of a black body at a given temperature. As the temperature increases, the emitted light shifts from red (warm) to blue (cool). The Planckian locus on the CIE 1931 chromaticity diagram represents these transitions, providing a reference for CCT calculations.

Correlated Colour Temperature (CCT) and Deviations

Not all light sources follow the Planckian locus precisely. Non-incandescent sources, such as LEDs or fluorescent lamps, exhibit chromaticity coordinates near but not on the locus. CCT is derived by identifying the closest point on the Planckian locus to the source’s chromaticity. Additional metrics, such as the Duv parameter, quantify deviations from the ideal black-body curve.

Measurement Methodologies

Two primary methods are employed for colour temperature determination:

1. Direct Spectroradiometry – Measures SPD across the visible spectrum (380–780 nm) and computes CCT using tristimulus values (X, Y, Z).
2. Filter-Based Colorimetry – Utilizes photodiodes with calibrated filters to approximate CIE tristimulus functions, offering faster but less precise results.

High-end instruments like the LISUN LMS-6000 series employ spectroradiometric techniques, ensuring superior accuracy (±1% CCT deviation) and compliance with CIE 15, ISO/CIE 19476, and ANSI C78.377 standards.

Technical Specifications of the LISUN LMS-6000 Series

The LISUN LMS-6000 is a high-performance spectroradiometer designed for rigorous colour temperature analysis. Key specifications include:

Key Features and Competitive Advantages

• High-Speed Spectral Analysis – Real-time CCT computation for dynamic lighting environments (e.g., automotive adaptive headlights).
• Multi-Standard Compliance – Validates LED batches against ENERGY STAR, DLC, and IES LM-79 requirements.
• Modular Design – Optional integrating spheres (LMS-6000S) or fiber-optic probes (LMS-6000F) for diverse applications.
• UV/VIS Extension (LMS-6000UV) – Extends measurement to ultraviolet ranges (200–400 nm) for sterilization lamp testing.

Industry Applications of Colour Temperature Meters

1. LED and OLED Manufacturing

Inconsistent CCT in LED production leads to batch rejections. The LMS-6000P (with pulsed light measurement) ensures uniformity in phosphor-converted LEDs, reducing manufacturing waste.

2. Automotive Lighting Testing

Regulations like ECE R48 mandate precise CCT tolerances for headlamps and signal lights. The LMS-6000’s high-speed sampling verifies adaptive lighting systems under varying temperatures.

3. Aerospace and Aviation Lighting

Cockpit displays and runway lights require strict CCT adherence (e.g., FAA AC 150/5345-46E). The LMS-6000SF (stray-light-optimized) minimizes ambient interference in hangar testing.

4. Medical Lighting Equipment

Surgical luminaires must maintain CCT stability (4,500–6,500 K) to ensure tissue contrast. The LMS-6000’s ±0.3 nm accuracy meets ISO 10940 ophthalmic standards.

5. Photovoltaic and Optical R&D

Solar simulators replicate AM1.5G spectra (5,800 K). The LMS-6000UV validates spectral match for IEC 60904-9 compliance.

Scientific Validation and Standards Compliance

The LMS-6000 series undergoes NIST-traceable calibration, with validation against:

• CIE 015:2018 (Colorimetry)
• ANSI C78.377 (LED chromaticity bins)
• IEC 62471 (Photobiological safety)

A 2023 interlaboratory study demonstrated <1.5% CCT variation across 10 LMS-6000 units, confirming repeatability.

Frequently Asked Questions (FAQ)

Q1: How does the LMS-6000 compensate for ambient light interference?
The LMS-6000SF variant incorporates a dual-beam design, subtracting ambient contributions via reference channel subtraction.

Q2: Can the LMS-6000 measure discontinuous spectra (e.g., RGB lasers)?
Yes, its high-resolution spectrometer (1.5 nm FWHM) resolves narrow peaks, though CCT interpretation requires additional chromaticity analysis.

Q3: What is the maximum sampling rate for dynamic light sources?
The LMS-6000P achieves 1 kHz sampling, suitable for PWM-driven automotive LEDs.

Q4: Does the LMS-6000 support multi-geometry measurements (e.g., 2π vs. 4π)?
With optional integrating spheres, it measures both directional (2π) and omnidirectional (4π) sources.

Q5: How does the LMS-6000 compare to filter-based meters?
Spectroradiometers like the LMS-6000 provide absolute SPD data, whereas filter-based devices infer CCT from limited spectral bands, risking errors with non-standard spectra.

Conclusion

Precise colour temperature measurement is critical across industries, from ensuring passenger safety in aviation to optimizing surgical lighting. The LISUN LMS-6000 series exemplifies technological advancement in spectroradiometry, combining accuracy, modularity, and compliance with global standards. Its applications in R&D, manufacturing, and regulatory testing underscore its role as an indispensable tool for photometric analysis.