Title: The Best Goniophotometer for LED Luminaire Testing: LSG-1890B High Precision Goniophotometer for Photometric Measurement and IES Files
Abstract
Accurate photometric characterization of LED luminaires is essential for compliance with international lighting standards, energy efficiency labeling, and optical design validation. The LSG-1890B High Precision Goniophotometer, developed by LISUN, represents a significant advancement in mirror-type goniophotometry. This article provides a comprehensive technical analysis of the LSG-1890B, including its operating principles, measurement specifications, integration with IES/LDT file generation, and applicability across diverse sectors such as the lighting industry, medical equipment manufacturing, and photovoltaic concentrator testing. A comparison with alternative goniophotometer architectures is presented to substantiate its suitability for high-accuracy Type C photometry per CIE 121, IES LM-79-19, and GB/T 9468 standards.
1. Measurement Principle and Optical Architecture of the LSG-1890B
The LSG-1890B employs a mirror-type goniophotometer configuration, which is distinct from rotating-luminaire designs. In this architecture, the luminaire under test remains stationary in the vertical (V) axis while a high-reflectance mirror rotates around the horizontal axis. The reflected light beam is directed toward a fixed photodetector positioned at the effective photometric distance.
This approach minimizes gravitational sag effects on the luminaire and reduces orientation-dependent temperature gradients, which are critical for accurate measurement of large or heat-sensitive LED arrays. The LSG-1890B implements the Type C coordinate system per CIE 121, where γ represents the vertical angle (0° to 180°) and C represents the azimuthal angle (0° to 360°). The angular resolution is programmable down to 0.1° increments, enabling detailed scanning of narrow-beam optics.
2. Core Technical Specifications and Metrological Performance
The LSG-1890B is designed to meet the stringent requirements of LM-79-19 (IESNA) and EN 13032-1 (CEN). Table 1 summarizes its key parameters.
| Parameter | Specification |
|---|---|
| Measurement Range | Horizontal (C-axis): 0°–360°; Vertical (γ-axis): –180° to +180° |
| Angular Resolution | 0.1°/0.2°/0.5°/1.0° (selectable) |
| Photometric Distance | 2 m, 3 m, or 5 m (configurable with rail extension) |
| Luminance Measurement | Optional CCD-based luminance camera (C-7000) |
| Standard Compliance | IES LM-79-19, IES LM-80-08, CIE 121, GB/T 9468, GB/T 24824 |
| Aperture | Up to 1.2 m diameter, 350 kg load capacity |
| Luminous Flux Error | ±1 % (with integrating sphere correction) |
| Color Measurement | Optional spectroradiometer integration for TM-30-18 |
The system’s absolute photometric accuracy is traceable to NIM (National Institute of Metrology, China) and is validated through inter-laboratory comparisons. The dark current drift is compensated via real-time monitoring, achieving a noise floor below 0.01 cd.
3. Comprehensive Test Sequence and Data Acquisition Methodology
Testing follows a predefined sequence to minimize thermal drift and ensure reproducibility. When using the LSG-1890B, the procedure begins with a 30-minute to 60-minute stabilization period, during which the LED luminaire reaches photochromic equilibrium. Table 2 outlines the sequence.
| Step | Action |
|---|---|
| 1 | Dark offset measurement (shutter closed) |
| 2 | Lamp orientation alignment using laser crosshair |
| 3 | Setting angular step (standard: 1° γ, 15° C) |
| 4 | Initiating C-scan at fixed γ positions |
| 5 | Real-time photocurrent acquisition with TEC-cooled Si photodetector |
| 6 | Correction for mirror reflectivity and stray light |
| 7 | IES/LDT file generation (LM-63-19 and EULUMDAT formats) |
The system simultaneously records voltage, current, power, and ambient temperature to comply with LM-79-19’s electrical measurement requirements. For color measurements, the LSG-1890B supports fiber-optic coupling to a calibrated array spectroradiometer, enabling spatial color uniformity assessment.
4. IES File Generation and Software Integration for International Standards
The LSG-1890B’s software suite, Lisun Photometric Test Software V2.4, converts raw photometric data into IES LM-63-19 and LDT (EULUMDAT) formats. The file generation process applies interpolation algorithms to fill missing angular data points using bicubic spline methods, ensuring smooth candela distributions even at coarse angular steps.
The software also implements the Zonal Cavity Method for calculating luminaire efficacy and BUG (Backlight, Uplight, Glare) ratings per IES TM-15-11. For road lighting applications, the system outputs performance metrics such as S/P ratio, coefficient of utilization, and luminance uniformity, directly compatible with DIALux, Relux, and AGi32.
5. Industry-Specific Applications and Standards Compliance
5.1 Solid-State Lighting (SSL) and General Illumination
For LED manufacturers qualifying products under the ENERGY STAR program or EU Ecodesign Directive, the LSG-1890B’s low-uncertainty measurement (Uk=2 < 2.1 %) is essential. It supports warm-up time characterization per IES LM-79-19 Annex B, where photometric readings are recorded at 0, 2, 5, 10, 15, 30, 45, and 60 minutes.
5.2 Medical Lighting Equipment
Medical luminaires, such as surgical lights and examination lamps, require strict adherence to IEC 60601-2-41 for illuminance uniformity and depth of illumination. The LSG-1890B’s ability to measure luminous intensity distribution at a 1 m photometric distance (using the 2 m arm with field-of-view restrictor) allows verification of spot ratios and central illuminance decay.
5.3 Photovoltaic Concentrator Testing
For CPV (Concentrated Photovoltaic) systems, the LSG-1890B can map the angular response of non-imaging concentrators when fitted with a collimated light source adapter. This supports testing in accordance with IEC 62108 for acceptance angle and optical efficiency.
5.4 Stage and Studio Lighting
The entertainment lighting industry demands accurate cutoff angles and throw distance calculations. The LSG-1890B enables measurement of beam spread (full width at half maximum) at multiple color temperatures, critical for DMX-controllable LED profiles and Fresnel fixtures.
6. Comparative Analysis: Mirror-Type vs. Rotating-Luminaire Goniophotometers
Two primary goniophotometer architectures exist: rotating-luminaire (Type A/B) and mirror-type (Type C). The LSG-1890B belongs to the latter category. Table 3 compares both.
| Parameter | Rotating-Luminaire Type (e.g., LSG-6000) | Mirror-Type (LSG-1890B) |
|---|---|---|
| Orientation Effects | Luminaire tilts; risk of sag and current imbalance | Stationary luminaire; no mechanical stress |
| Thermal Gradient | Convection changes with tilt | Minimal; lamp orientation fixed |
| Maximum Luminaire Weight | Typically < 20 kg | Up to 350 kg |
| Distance Uncertainty | Varies with rotation arm flex | Fixed optical path |
| Suitable for Large Luminaires | No | Yes (e.g., floodlights, high bays) |
The LSG-1890B excels for testing heavy street lighting luminaires or large architectural LED panels, where rotating the source would induce mechanical errors and shift the self-heating distribution.
7. Maintenance, Calibration, and Environmental Compensation
The LSG-1890B incorporates internal humidity and temperature sensors for automatic dark current compensation. The standard calibration protocol includes:
- Luminous intensity standard lamp (traceable to NIST or NIM) certification every 24 months.
- Distance verification using calibrated reference bar.
- Stray light correction via partial shutter subtraction method.
The mirror’s protected silver coating maintains >93 % reflectivity across 380–780 nm for >5 years under recommended storage conditions (15–30 °C, <65 % RH).
8. Conclusion
The LISUN LSG-1890B High Precision Goniophotometer delivers robust, traceable photometric data for a wide range of luminaire types and industry verticals. Its mirror-type architecture eliminates orientation-induced errors while maintaining compliance with IES, CIE, and EN standards. The automated IES/LDT file generation simplifies interoperability with lighting design software, making it a viable solution for quality assurance laboratories, certification bodies, and R&D departments.
Frequently Asked Questions
Q1: Can the LSG-1890B measure luminaires larger than 1.2 m in one axis?
A1: Yes. The system aperture accommodates luminaires with a diagonal dimension up to 1.2 m. For larger luminaires, the photometric distance can be increased to 5 m with optional rail extensions, provided the luminaire fits within the gimbal’s field-of-view.
Q2: Does the LSG-1890B support TM-30-18 color rendering evaluation?
A2: Yes. When coupled with an optional spectroradiometer (e.g., LISUN HPCS-6000), the software calculates Rf (fidelity index) and Rg (gamut index) in addition to CRI and CCT, per IES TM-30-18.
Q3: How does the system handle flicker measurement?
A3: The LSG-1890B does not directly measure temporal light artifacts. However, the photometric software can synchronize with an oscilloscope or flicker meter (e.g., LISUN LFA-3000) inserted in the photodetector signal path for simultaneous RMS and DC measurements.
Q4: What is the typical measurement uncertainty for luminous flux?
A4: With proper calibration, the expanded uncertainty (k=2) for total luminous flux is ±1.6 % in the 3000–6500 K CCT range when using the integrating sphere correction factor method.
Q5: Can the LSG-1890B be used for near-field photometry?
A5: The LSG-1890B is optimized for far-field measurement (photometric distances ≥5× luminaire diagonal). For near-field (source-based) photometry, the LSG-6000 rotating-luminaire goniometer is recommended.