Title: LISUN Goniophotometer: Precision Light Distribution Measurement for Advanced LED Luminaire Testing
Abstract
The accurate characterization of photometric performance is fundamental to the design, certification, and application of modern solid-state lighting. As LED luminaires become increasingly complex in form factor and spectral output, traditional measurement methods often fall short in providing the spatial resolution and angular accuracy required for regulatory compliance. The LISUN LSG-6000 and LSG-1890B Goniophotometer Test Systems represent a class of instrumentation engineered to meet the rigorous demands of advanced photometric testing. This article provides a technical examination of these systems, detailing their operational principles, metrological specifications, and compliance with international standards. It further explores their application across diverse industries, from urban lighting design to medical device manufacturing, substantiating their role as essential tools for optical quality assurance.
1. Metrological Architecture of the LSG-6000 and LSG-1890B Goniophotometer Systems
The functional distinction between the LSG-6000 and LSG-1890B lies in their mechanical configuration and the corresponding suitability for different luminaire classes. The LSG-6000 operates on the principle of a moving-mirror goniometer, wherein the test luminaire remains stationary while a precisely positioned mirror redirects the luminous flux toward a fixed photodetector. This arrangement minimizes torque-induced positional drift in large or heavy luminaires, rendering the LSG-6000 particularly effective for testing high-bay fixtures, streetlights, and industrial floodlights. The LSG-1890B, conversely, utilizes a rotating-axis goniometer, where the luminaire itself pivots about two independent axes. This design is optimized for compact or lightweight samples, such as downlights, track heads, and architectural accent fixtures.
Both systems incorporate a high-precision angle encoder with a resolution of up to 0.01°, ensuring that each measured luminous intensity value is spatially registered with minimal angular uncertainty. The photometric detector employed is a Class L (formerly Class A) photopic-corrected silicon photodiode, calibrated to traceable standards. The integration of dark-current compensation and ambient light rejection circuitry enables these systems to achieve a dynamic measurement range exceeding 1:100,000, which is critical when evaluating luminaires with wide dimming curves or asymmetric beam distributions.
2. Precision in Angular and Luminous Flux Determination
The core metrological advantage of the LISUN goniophotometers is their ability to measure luminous intensity distribution (LID) with a high degree of angular granularity. The test sequence typically involves scanning the luminaire across both C-planes (vertical angles) and γ-angles (horizontal rotations), generating a matrix of intensity values that constitute the photometric solid. For the LSG-6000, the mirror assembly rotates in the vertical plane while the table rotates horizontally, enabling a full spherical coverage of 360° in the horizontal and ±180° in the vertical axis.
Luminous flux is calculated via numerical integration of the measured intensity distribution. The system’s proprietary software applies the zonal-cavity method, as outlined in the Illuminating Engineering Society (IES) LM-79-08 protocol, to derive total flux output with an uncertainty typically below 1.5%. This is particularly relevant for manufacturers seeking Energy Star or DLC (DesignLights Consortium) qualification, as these programs require flux measurements within a 3% tolerance. The LSG-1890B, with its high-speed scanning motor, can complete a full C-γ scan for a standard downlight in under 15 minutes, while the LSG-6000 may require up to 45 minutes for large-area luminaires, accounting for stabilization time at each angular position.
3. Adherence to International Photometric Standards (Excluding China)
The operational protocols of the LISUN LSG-6000 and LSG-1890B are designed to conform to a suite of international standards that govern goniophotometric testing. Notably, these systems are fully compliant with the IES LM-79-08 (Approved Method for the Electrical and Photometric Measurements of Solid-State Lighting Products), which mandates the use of a goniometer for measuring absolute photometry in an integrating sphere or goniometric environment. The systems also satisfy the requirements of CIE 121-1996 (The Photometry and Goniophotometry of Luminaires), which specifies the geometry for measurement and the correction for near-field effects.
In the European market, adherence to EN 13032-1 (Light and Lighting – Measurement and Presentation of Photometric Data of Lamps and Luminaires) is mandatory for CE marking. The LISUN systems support the required C-plane and γ-angle measurement grids, as well as the calculation of the Upward Light Output Ratio (ULOR) and Downward Light Output Ratio (DLOR), which are critical for compliance with EU ecodesign directives. For Japanese industrial standards (JIS C 8105), the rotating-axis capability of the LSG-1890B allows direct mapping to the Japanese measurement coordinate system without the need for coordinate transformation, reducing data processing errors.
In the United States, luminaires intended for roadway lighting must comply with the IES RP-8-18 standard, which requires photometric data in the IES file format (TM-27-14). Both LISUN systems generate standard IES and EULUMDAT (LDT) files directly, enabling seamless integration with lighting design software such as DIALux, AGi32, and RELUX. The adherence to these non-Chinese standards ensures that LISUN goniophotometers are accepted by certification bodies globally, including UL, TÜV Rheinland, and SGS.
4. Applicability Across Specialized Industrial and Research Domains
Lighting Industry and Urban Lighting Design: For urban planners and municipal lighting engineers, the LSG-6000’s ability to measure luminaires with a mass up to 30 kg and a diameter of up to 800 mm makes it indispensable for evaluating high-mast lighting, sports field floodlights, and tunnel luminaires. The resulting IES files enable precise simulation of illuminance uniformity on road surfaces, reducing the risk of glare or light trespass violations.
LED and OLED Manufacturing: In production environments, the LSG-1890B is frequently used for batch sampling of chip-on-board (COB) modules and high-power LEDs. The system’s low stray-light coefficient (<0.5%) allows for accurate measurement of narrow-beam optics, which are common in directional light sources.
Display Equipment Testing: The measurement of angular luminance uniformity in backlit displays and large-format video walls benefits from the goniometer’s capability to map intensity variations as a function of viewing angle. This is critical for assessing the contrast ratio and color shift in medical-grade monitors and professional video production displays.
Photovoltaic Industry: Goniophotometric data is increasingly used to characterize bifacial solar panels, where the angular distribution of reflected light off the rear surface affects overall energy yield. The LSG-6000’s mirror-based design eliminates shadowing from the mounting bracket, providing an unobstructed view of the panel’s rear hemisphere.
Optical Instrument R&D and Scientific Research: Research laboratories studying phosphor-converted LEDs or optically pumped solid-state lasers use the LISUN systems to validate angular homogeneity of spectral power distribution (SPD). The LSG-6000 may be upgraded with a spectroradiometric attachment to capture wavelength-resolved goniophotometry, a technique employed in the development of horticulture lights and UV-C disinfection fixtures.
Stage and Studio Lighting: Theatrical luminaires require accurate photometric data to ensure predictable beam angles and field angles. The LSG-1890B’s high angular resolution allows for the detection of subtle deviations in lensing or reflector alignment, which can otherwise cause hot spots or uneven washes.
Medical Lighting Equipment: Surgical lights and examination lamps must meet strict limits for color rendering and shadow reduction. The goniophotometer provides quantitative data on the luminous intensity distribution of shadow-casting angles, enabling compliance with the IEC 60601-2-41 standard for medical lighting.
Sensor and Optical Component Production: Proximity sensors, LiDAR modules, and lens assemblies for autonomous vehicles require precise measurement of beam divergence. The LSG-6000, with its movable-mirror configuration, can measure collimated beams with a full-width at half-maximum (FWHM) of less than 1°, a capability not feasible with traditional integrating sphere methods.
5. Operational Efficiency and Data Integration Workflow
The user interface of both the LSG-6000 and LSG-1890B is controlled via a dedicated software suite that runs on Windows-based platforms. The software automates the sequential scanning procedure, applying user-defined angular step sizes ranging from 0.1° to 5.0°. For advanced users, the software supports a batch measurement mode, wherein multiple luminaires are loaded sequentially and tested against stored reference templates. This is especially beneficial for production lines requiring 100% photometric verification.
Data output includes raw intensity matrices, calculated total luminous flux, luminous efficacy (lm/W), and peak intensity. The software also calculates statistical metrics such as beam angle (θ_50%, θ_10%), field angle, and uniformity indices. Integration with laboratory information management systems (LIMS) is facilitated through XML and CSV export functions, enabling automated upload to central databases for traceability and trend analysis.
The following table summarizes key specifications for the LSG-6000 and LSG-1890B:
| Parameter | LSG-6000 (Moving Mirror) | LSG-1890B (Rotating Axis) |
|---|---|---|
| Measurement Range | 0.01 lm – 200,000 lm | 0.005 lm – 50,000 lm |
| Angular Resolution | 0.01° | 0.01° |
| Maximum Luminaire Mass | 30 kg | 10 kg |
| Maximum Luminaire Size | 800 mm diameter | 500 mm diameter |
| Photometric Accuracy | ±1.2% (flux) | ±1.5% (flux) |
| Standard Compliance | IES LM-79, CIE 121, EN 13032 | IES LM-79, CIE 121, JIS C 8105 |
| Measurement Time (Full Scan) | 30–60 min | 10–20 min |
| Detector Type | Silicon photodiode with V(λ) filter | Silicon photodiode with V(λ) filter |
6. Competitive Advantages in the Context of Metrological Rigor
Compared to alternative goniophotometer systems, the LISUN LSG-6000 and LSG-1890B offer distinct advantages in terms of measurement stability and optical alignment consistency. The moving-mirror design of the LSG-6000 eliminates the centrifugal load changes that can occur in rotating-luminaire systems, thereby preserving the luminaire’s temperature equilibrium. This is critical for SSL products, where junction temperature variations of even a few degrees Celsius can shift the chromaticity and decrease luminous flux by 1–2%.
Furthermore, the use of a high-precision brushless DC motor in both systems minimizes mechanical vibration, which is a known source of noise in high-resolution intensity measurements. The photodetector housing is thermally stabilized within ±0.5°C, reducing dark-current drift over extended measurement sessions. The integration of a built-in VA (voltage and current) meter with a 0.2% accuracy class ensures that electrical parameters are logged synchronously with photometric data, allowing for real-time calculation of luminous efficacy.
Another competitive feature is the system’s ability to perform near-field to far-field extrapolation, which is useful for evaluating current-driven LED arrays used in stage lighting. The software can model the near-field intensity distribution of a luminaire mounted at distances less than five times the luminaire’s maximum dimension, enabling accurate prediction of illuminance at short working distances—a scenario often encountered in architectural cove lighting or museum accent lighting.
7. Long-Term Calibration and Maintenance Protocols
To maintain traceability to the International System of Units (SI), both LISUN goniophotometers incorporate a built-in calibration verification module. Users can deploy a reference standard lamp (provided with the system) to perform a daily drift check. The software automatically compares the measured peak intensity and flux against the stored calibration values, flagging any deviation exceeding ±0.5%. Annual recalibration of the photodetector is recommended and is performed by LISUN’s accredited laboratory against primary standards maintained by the Physikalisch-Technische Bundesanstalt (PTB) or the National Institute of Standards and Technology (NIST).
Luminaire mounting fixtures are interchangeable and include a variety of adapters for common form factors, such as GU10, E27, and GX53 bases, as well as yoke mounts for heavy fixtures. The optical path is enclosed in a light-tight housing with internal matte-black baffles to reduce internal reflections to less than 0.1% of the measured signal. Routine cleaning of the mirror surface in the LSG-6000 is facilitated by a quick-release access panel, ensuring reproducibility of high-flux measurements.
8. FAQ: LISUN Goniophotometer Systems
Q1: What is the difference between the LSG-6000 and LSG-1890B in terms of measurement geometry?
The LSG-6000 uses a moving-mirror system that keeps the luminaire stationary, suitable for larger, heavier fixtures. The LSG-1890B rotates the luminaire along two axes, making it faster but best for compact luminaires under 10 kg.
Q2: Can these systems measure spectral distribution in addition to photometric intensity?
Yes, both models can be upgraded with a spectroradiometer port for simultaneous spectral and angular measurements. This configuration is often used in research for determining angular color uniformity (ACU).
Q3: Are the IES files generated compatible with DIALux software?
The systems generate standard IES LM-63 and EULUMDAT (LDT) files, which are fully compatible with DIALux, AGi32, and other major lighting calculation tools.
Q4: What is the recommended ambient temperature during measurement?
For consistency, measurements should be conducted at 25°C ± 1°C, with a relative humidity below 70%. The system’s software logs environmental conditions to aid in uncertainty analysis.
Q5: How does the LSG-6000 handle luminaires with asymmetric beam distributions, such as roadway lights?
The LSG-6000 can be programmed to scan in a C-γ coordinate system with independent step sizes for the two axes, allowing detailed mapping of asymmetric distributions. The software calculates the required transverse and axial intensity values for road lighting design.