A Comprehensive Technical Analysis of the LISUN LSG-6000 and LSG-1890B Goniophotometers for LM-79 Compliance Testing
Abstract
Accurate photometric measurement is a cornerstone of modern lighting engineering, particularly for solid-state lighting (SSL) products such as LEDs and OLEDs. The LISUN LSG-6000 and LSG-1890B Goniophotometer systems represent precision instruments designed to perform absolute photometry in strict accordance with the IES LM-79-19 standard. This article provides a detailed technical examination of these systems, covering their operational principles, mechanical configurations, optical measurement chains, data acquisition methodologies, and compliance with international standards such as IES LM-79, CIE 121, and ENERGY STAR requirements. Performance specifications, comparative advantages, and application-specific modifications for diverse industries—including medical lighting, photovoltaic R&D, and stage lighting—are discussed. A FAQ section addresses common technical inquiries regarding system calibration, reference standards, and measurement uncertainty.
1. Operating Principle of the LISUN Type-C Goniophotometer Configuration
The LSG-6000 and LSG-1890B systems employ a Type-C goniophotometer architecture, which is defined by the movement of the source about two orthogonal axes (C and γ) while the detector remains fixed. The system utilizes a rotating mirror mechanism to maintain a constant photometric distance without physically repositioning the luminaire. The luminaire under test is mounted on an adjustable platform, which rotates around a vertical axis (C-axis, typically 0° to 360°) and a horizontal axis (γ-axis, typically 0° to 180°).
A key distinction of the Type-C arrangement is the use of a plane mirror to reflect the light output towards a stationary photodetector. This design eliminates errors associated with detector movement and ensures a fixed measurement geometry, a mandatory requirement for LM-79 absolute photometry. The angular encoder resolution on both axes is 0.1° for the standard model, with optional high-resolution encoders achieving 0.01° for the LSG-1890B variant. The photocurrent is measured by a calibrated photometer head, typically a Class A (Lux meter) according to CIE 69, which is corrected for spectral mismatch (f1’ < 3%).
2. Mechanical Specifications and Load Capacity Differentiation: LSG-6000 vs. LSG-1890B
The primary mechanical distinction between the LSG-6000 and LSG-1890B lies in load capacity and spatial envelope, which directly influence the range of luminaire geometries that can be tested.
| Parameter | LSG-6000 | LSG-1890B |
|---|---|---|
| Maximum Luminaire Weight | 50 kg | 100 kg |
| Rotational Axis Range | C: 0–360°, γ: 0–180° | C: 0–360°, γ: 0–180° |
| Distinctive Feature | Compact footprint, suitable for LED downlights, panels, and automotive lamps | Heavy-duty frame, intended for high-bay, street lighting, and stadium fixtures |
| Angular Resolution (Standard/Optional) | 0.1° / 0.05° | 0.1° / 0.01° |
| Maximum Luminaire Dimension | 2 m diameter | 3 m diameter |
The LSG-1890B incorporates reinforced bearings and a stiffer torque tube to accommodate luminaires weighing up to 100 kg, such as large area OLED panels or heavy industrial LED floodlights. Conversely, the LSG-6000 prioritizes reduced mechanical inertia for faster testing cycles typical of high-volume quality assurance in LED manufacturing.
3. Optical Measurement Chain and Photometric Accuracy
The optical measurement chain consists of three critical components: a high-stability power supply, a photometric photometer, and a spectral radiometer for colorimetric data. LISUN systems integrate a PM-3000 series photometer (CIE f1’ < 1.5%) and a PMS-80 spectroradiometer for simultaneous total luminous flux (TLF) and chromaticity coordinate (CIE 1931 x,y) acquisition.
The system’s calibration traceability is established through a NIST-traceable luminance standard (halogen FEL lamp). The photometer is calibrated against a LISUN-supplied standard lamp of known spectral power distribution. The angular alignment is verified using a collimated laser diode placed at the center of rotation. For the LSG-1890B, the optical path length is adjustable between 2 m and 5 m, enabling far-field measurement of large luminaires without violating the inverse-square law.
4. Compliance with IES LM-79-19 and CIE S 025:2018
The LSG-6000 and LSG-1890B are engineered to meet the absolute photometry requirements of IES LM-79-19 (Approved Method: Electrical and Photometric Measurements of Solid-State Lighting Products). This standard mandates testing at 25°C ± 1°C ambient temperature, with a thermal stabilization period of at least 30 minutes for typical LED products.
Key compliance features include:
- Goniophotometer Type: Type-C with mirror rotation, fulfilling the LM-79 requirement for a fixed detector.
- Photometric Distance: A minimum distance of 5 times the largest luminaire dimension is automatically maintained, with the option to increase to 15 meters for large fixtures.
- Color Measurement: The PMS-80 spectroradiometer provides correlated color temperature (CCT), color rendering index (Ra), TM-30 Rf/Rg, and chromaticity tolerance (SDCM) in compliance with ANSI C78.377.
- Electrical Measurement: The system includes a high-precision digital power meter (SP-HL series) for measuring input voltage, current, power factor, and total harmonic distortion (THD) per IEC 61000-3-2.
Additionally, the system supports the CIE S 025:2018 standard for test methods for LED lamps, luminaires, and modules, which is the European norm adopted by JIS in Japan and KS in South Korea.
5. Data Acquisition Software and Spatial Intensity Distribution Modeling
The control software, LISUN Goniometer Professional v5.0, orchestrates the entire measurement sequence, including calibration, data collection, and report generation. The software implements a multi-step scan algorithm that preferentially acquires photometric data at finer angular increments (e.g., 0.5°) near the luminaire’s beam axis and coarser increments (2.5°) in the periphery, optimizing test duration without sacrificing accuracy.
Output data formats include:
- IES LM-63-19 standard photometric files (.ies) for use in AGi32, Dialux, and Relux.
- CIE 102 format for .ldt files (EULUMDAT).
- Customizable CSV and XML formats for R&D internal databases.
The software calculates physiological photometric parameters such as Unified Glare Rating (UGR per CIE 117), utilization factor tables, and luminaire classification system (LCS) for road lighting per CIE 140. For medical lighting applications, the software includes a module for assessing color uniformity in the beam pattern per IEC 60601-2-41.
6. Application in LED and OLED Manufacturing: Production Line Implementation
In LED manufacturing environments, the LSG-6000 is frequently integrated into inline quality control loops. The system’s automated clamping and rotation functions allow a typical cycle time of 3–5 minutes for a single LED downlight. This throughput is sufficient for batch sampling per AQL standards (ISO 2859-1).
For OLED panel testing, the LSG-1890B’s larger aperture and higher load capacity are advantageous. OLED panels often require non-standard mounting due to their planar geometry and thermal sensitivity. The system’s temperature-controlled mounting plate (optional ±0.5°C accuracy) meets the stringent requirements of IES LM-80 for lumen maintenance testing, allowing the goniophotometer to double as a test station for accelerated aging studies.
7. Photovoltaic Industry: Spectral and Luminous Efficacy Characterization
In photovoltaic R&D laboratories, the LSG systems serve a dual purpose: measurement of luminous efficacy of solar simulators and characterization of light sources used in concentrated photovoltaic (CPV) testing. The spectroradiometer can be calibrated for absolute irradiance (W/m²/nm) via a NIST-traceable irradiance standard, allowing the system to evaluate the spectral mismatch parameter (MMF) per ASTM E973.
Furthermore, the goniophotometer can map the angular intensity distribution of a calibrated light source used in a solar simulator, ensuring compliance with IEC 60904-9 for spectral match, spatial non-uniformity, and temporal instability. This capability is critical for manufacturers of high-concentration photovoltaic modules requiring collimated beam characterization.
8. Medical and Surgical Lighting: Compliance with IEC 60601-2-41
Medical lighting equipment, such as surgical luminaires, requires precise photometric characterization under IEC 60601-2-41 (Particular requirements for the basic safety and essential performance of surgical luminaires). The standard mandates measurement of illuminance at varying distances (typically 1 m), depth of illumination, field diameter, and center-to-surround ratio (CSR).
The LSG-1890B is favored in this sector due to its ability to mount heavy surgical pendant heads. The software includes a dedicated module for:
- Illuminance distribution at the surgical field (600 mm × 400 mm area).
- Color temperature stability during dimming scenarios.
- Luminance uniformity within the central field.
The high-resolution angular capacity (0.01°) of the LSG-1890B is essential for resolving the sharp beam cutoff characteristics of modern LED surgical lights.
9. Stage and Studio Lighting: Color Rendition and Beam Profile Analysis
For moving heads, follow spots, and wash lights in the entertainment industry, the goniophotometer must capture complex spatial color distributions. The LSG-6000 with an optional color mapper can produce a 2D false-color plot of CCT and Duv across the beam at any γ and C angle. This functionality supports compliance with ANSI E1.9 (Reporting Photometric Performance Data for Entertainment Luminaires).
The system’s ability to measure candela distribution at fine angular resolution (0.1°) allows for accurate generation of beam angles, field angles, and gonio-colorimetric data necessary for virtual light simulation in pre-visualization software (e.g., Vectorworks, WYSIWYG).
10. Urban Lighting and Roadway Photometric Design: CIE 140/144 Data Generation
Urban lighting design relies on photometric metrics such as road surface luminance, uniformity ratios (U0, UI), and threshold increment (TI). The LSG-1890B’s large load capacity accommodates heavy LED street luminaires. The photometric data derived from the system is input into lighting design software to calculate compliance with CIE 140 (Road Lighting Calculations) and EN 13201 (European Road Lighting Standard).
The software automatically generates utilization factor curves, waste light ratio (WLR) for full-cutoff fixtures, and obtrusive light assessments per CIE 150. Municipalities in countries such as South Korea, Germany, and the UAE have adopted LISUN goniophotometers as reference instruments for type approval testing of public lighting equipment.
11. Sensor and Optical Component Production: Radiant Intensity Pattern Characterization
Manufacturers of photodiodes, infrared emitters, and optical components utilize the LSG-6000 for characterizing the angular radiant intensity pattern. The system can be configured with a calibrated photodiode and radiometric lens for measurement in the UV, VIS, and NIR bands (300 nm to 1100 nm). This is particularly relevant for VCSEL (Vertical-Cavity Surface-Emitting Laser) testing in LiDAR and 3D sensing applications, where the beam divergence half-angle must be quantified with sub-0.05° precision.
12. Competitive Technological Advantages Over Alternative Goniophotometer Architectures
Compared to moving-detector (Type A/B) goniophotometers, the LISUN Type-C mirror-based design offers several quantifiable advantages:
- Reduced Alignment Error: The photometer remains stationary, eliminating positional uncertainty introduced by robotic arm movement.
- Lower Stray Light: The mirror coating (>95% reflectivity in visible range) minimizes Fresnel reflections inherent in moving detector configurations.
- Thermal Stability: The stationary detector can be maintained in a temperature-controlled enclosure, reducing dark current drift.
- Standardized Retrofit: The LSG-1890B can accommodate a DTR-2000 integrating sphere for simultaneous measurement of total spectral flux, reducing total test time.
Furthermore, LISUN systems offer a dynamic range of over 100,000:1 in photometric measurement due to the use of a photomultiplier tube (PMT) for low-level signals and a silicon photodiode for high-level signals, a hybrid approach not commonly found in competing products.
13. Calibration Methodology and Long-Term Stability Verification
Routine calibration verification is performed using a secondary standard lamp (SI-traceable) mounted at the center of rotation. The calibration protocol involves a four-step process:
- Dark current subtraction: Measured for 60 seconds before each measurement cycle.
- Photometric distance verification: Using a red laser grid to confirm the 5-meter optical path.
- Spectral mismatch correction: Calculated from the spectroradiometer’s measured SPD and the photometer’s spectral responsivity.
- Angular encoder zeroing: A magnetic switch ensures the goniometer returns to its home position within ±0.01°.
Annual recalibration through LISUN’s service center or a partner laboratory in the EU or USA is recommended to maintain accreditation under ISO 17025.
Frequently Asked Questions (FAQ)
Q1: What is the maximum acceptable measurement uncertainty for a LSG-6000 goniophotometer under LM-79?
The expanded uncertainty (k=2) for total luminous flux measurement is typically ±1.8% for a well-maintained system, assuming a calibrated standard lamp and proper spectral mismatch correction. This is within the ±3% threshold recommended by LM-79 for absolute photometry.
Q2: Can the LSG-1890B be used to test large outdoor floodlights with asymmetrical beam patterns?
Yes. The LSG-1890B’s heavy-duty rotation axis and wide angular range (γ: 0°–180°) handle asymmetrical distributions effectively. The software automatically applies correction for the luminaire’s tilt during measurement and generates IES files that accurately represent the beam pattern for vertical and horizontal planes.
Q3: How does the system correct for the mirror’s spectral reflectivity variation across the visible spectrum?
A pre-calibrated mirror correction factor table is stored in the software. This table applies a wavelength-dependent correction to the measured photocurrent based on the known spectral reflectivity of the mirror coating. The system automatically interpolates this data using the spectroradiometer’s measured SPD.
Q4: Is it possible to integrate the goniophotometer with an environmental chamber for temperature-dependent measurements?
Yes. LISUN offers an optional thermal chamber (e.g., LSG-TC series) that encloses the luminaire and mirror assembly. This allows testing per IES LM-80 (lumen maintenance) and/or ISTMT (In-Situ Temperature Measurement) protocols at temperatures ranging from 10°C to 50°C.
Q5: What file exchange formats are supported for compatibility with European lighting design software (Dialux, Relux)?
The system supports IES LM-63 (.ies), EULUMDAT (.ldt per CIE 102), and CIBSE TM-14 (.cib) formats. All standard European and North American design software are fully supported. Custom LDT file generation for photometric data exchange with Chinese GB/T 24980 is also available.