Title: The Role of the Goniophotometer in Photometric Testing and Light Distribution Measurement: A Technical Analysis of the LISUN LSG-6000/1890B Systems
Abstract
Accurate photometric testing is foundational to modern lighting design, quality assurance, and regulatory compliance. Central to this discipline is the goniophotometer, an instrument that measures the spatial distribution of luminous intensity from a source. This article examines the functional principles, measurement standards, and industry applications of goniophotometers, with a detailed focus on the LISUN LSG-6000 and LSG-1890B test systems. By integrating high-precision mechanics with spectroradiometric capabilities, these systems enable conformity to CIE, IESNA, and LM-79-19 testing protocols, serving critical roles in LED manufacturing, automotive lighting, photovoltaics, and medical device verification.
H2: Functional Principles of Goniophotometry in Luminous Intensity Mapping
A goniophotometer operates by rotating a light source or detector around multiple axes to capture the angular distribution of luminous intensity. The LSG-6000 and LSG-1890B employ a moving-mirror goniometer configuration, where the light source remains stationary while mirrors redirect the beam toward a fixed photometric detector. This design minimizes mechanical stress on the test specimen, which is essential for large, heavy luminaires or temperature-sensitive LED arrays.
The fundamental measurement is the far-field condition, defined as a distance of at least five times the maximum dimension of the light source. The LSG-6000 achieves this with a 5-meter test distance, while the LSG-1890B operates at 2.5 meters, compliant with CIE Publication 70. Angular resolution is adjustable down to 0.1°, allowing for detailed capture of narrow-beam optics used in stage lighting or directional photovoltaic concentrators. The data is exported in standard IES LM-63 and EULUMDAT formats, enabling direct import into lighting design software such as Dialux or Relux.
H2: Distinction Between Type C, A, and B Goniometer Configurations in the LSG Series
The LSG-6000 and LSG-1890B are configured as Type C goniophotometers according to the CIE classification system. In Type C geometry, the measurement axes correspond to horizontal (γ or C) and vertical (β) angles, with the lamp’s axis aligned to the vertical plane. This configuration is the international standard for general lighting and display testing, as it replicates real-world mounting orientations.
Type A (used for automotive headlamps) and Type B (for collimated sources) are less common in general photometry. The LSG series adapts to Type A testing via software-controlled axis redefinition, allowing the system to serve dual purposes for manufacturers producing both architectural and vehicular lighting. For example, a luminaire manufacturer evaluating a streetlight for EN 13201 compliance can switch to Type B for collimated medical endoscope measurement without hardware changes.
H2: LISUN LSG-6000/1890B – Technical Specifications and Optical Path Architecture
The LSG-6000 supports test specimens up to 30 kg and 1.6 m in diameter, while the LSG-1890B accommodates 10 kg and 0.6 m, making the latter ideal for smaller LED modules or laboratory prototypes. Both systems integrate a high-speed photometer (V(λ) corrected, Class L) with a dynamic range of 0.01 lx to 200,000 lx and uncertainty below ±3% at k=2.
A key differentiator is the dual-axis control via stepper motors with optical encoders, achieving ±0.1° positioning accuracy. The included PMT-1200 software performs automated scans at user-defined angular intervals, with typical measurement times of 10–30 minutes depending on resolution. For spectral analysis, an integrated spectroradiometer (optional for LSG-1890B, standard for LSG-6000) provides correlated color temperature (CCT) and color rendering index (CRI) data at each measured angle.
Table 1: Comparative Specifications of LSG-6000 and LSG-1890B
| Parameter | LSG-6000 | LSG-1890B |
|---|---|---|
| Max Test Distance | 5 m | 2.5 m |
| Max Luminaire Weight | 30 kg | 10 kg |
| Angular Accuracy | ±0.1° | ±0.2° |
| Photometer Class | L (CIE 69) | L (CIE 69) |
| Spectral Range (optional) | 380–780 nm | 380–780 nm |
H2: Compliance with IEC, IESNA, and National Standards – A Cross-Industry Requirement
The LSG series facilitates adherence to multiple international standards beyond China’s GB/T standards. For the European Union, compliance with EN 13032-1 and EN 13201 is critical for road lighting. In the United States, the IESNA LM-79-19 standard governs electrical and photometric testing of solid-state lighting, requiring both total flux (integrating sphere) and spatial distribution (goniophotometer) measurements. The LSG systems are validated against LM-79 Annex A, with angular measurement intervals of 1° for intensity distribution and 2.5° for chromaticity data.
For the photovoltaic industry, the IEC 60904-9 standard classifies solar simulators but also requires angular response characterization of concentrator cells. The LSG-6000, with its high-torque rotating arm, can map the angular sensitivity of photovoltaic modules under AM1.5G spectrum, an application increasingly demanded for building-integrated photovoltaics (BIPV). Similarly, medical lighting (IEC 60601-2-41) for surgical luminaires requires measurement of illuminance uniformity at working distances; the LSG’s ability to generate polar candela plots directly supports this verification.
H2: Application in LED and OLED Manufacturing – Angular Color Uniformity Analysis
In the manufacturing of high-power LEDs for automotive headlamps (e.g., Osram Oslon Black Flat), angular color non-uniformity (ACU) is a critical yield parameter. The LSG-6000’s integration of a spectroradiometer with a 2° receptor allows simultaneous measurement of luminous intensity and chromaticity at each angular step. For a typical 120° Lambertian LED, the system can detect deviations greater than 100 K in CCT across the beam angle, triggering a reject in QA workflows.
OLED panels used in display equipment require extremely low angular color shift, often specified at Δu‘v’ < 0.004 across ±60°. The LSG-1890B, with its compact size and fast scanning rates, can test up to 200 OLED samples per 8-hour shift. Data visualization tools in the software plot iso-candela curves and chromaticity contours, enabling engineers to correlate manufacturing parameters (e.g., evaporation rate) with optical performance.
H2: Urban Lighting Design and the Role of Goniophotometric Data in Pole Spacing Calculations
For urban lighting engineers, the IES file generated by the LSG series is the input for calculating pole spacing, uniformity ratios, and glare indices. The LSG-6000 is frequently used by municipalities in Europe for validating LED streetlight replacements. According to EN 13201, a luminaire’s luminous intensity distribution must be measured at least every 50 m in the road surface plane. The LSG-6000’s ability to produce 3D candela distributions with <3% total flux error reduces the need for iterative field testing.
In a case study from a Berlin-based lighting consultancy, replacement of high-pressure sodium fixtures with LED units tested on the LSG-6000 resulted in a 38% reduction in energy consumption while maintaining an average road surface luminance of 1.5 cd/m², measured per CIE 140. The goniophotometer also provided data for the Thiessen polygon method, optimizing pole placement to avoid dark zones.
H2: Stage and Studio Lighting – Beam Angle and Field Angle Verification
Stage lighting fixtures, such as moving heads and ellipsoidal reflectors, require precise beam angles (often defined as the angle where intensity falls to 50% of maximum) and field angles (10% of maximum). The LSG-1890B’s fine resolution of 0.1° is particularly suited for testing LED-based spotlights with zoom optics. For a typical 5°–35° zoom fixture, the goniophotometer must capture intensity changes of several hundred candelas within a few degrees; mechanical backlash below 0.05° in the LSG series ensures repeatable results.
Furthermore, the test system calculates the zonal flux per CIE Classification (for example, zonal 0–20°, 20–40°), directly useful for stage designers needing to calculate throw distances. The software outputs graphed polar diagrams and IES files that follow the 2002 IESNA format, ensuring compatibility with Vectorworks Spotlight or grandMA3’s visualizer.
H2: Sensor and Optical Component Production – Measuring Receiver Angle Response
Manufacturers of photodiodes, LIDAR receivers, and ambient light sensors require angular response characterization up to ±80°. The LSG-1890B’s rotating arm can mount a sensor on the specimen table and rotate a calibrated tungsten halogen source. By measuring output voltage vs. angle, the system derives the cosine response error, a key metric for lux meter calibrators. For example, a sensor intended for automotive rain-light sensors must maintain <5% deviation from the ideal cosine curve up to 60°.
The LSG-6000, with its larger torque, can handle heavy sensor housings (e.g., industrial LiDAR units weighing 15 kg). During testing, the software can display a polar plot of relative sensitivity, overlaying the manufacturer’s specification limits. This application is increasingly relevant for automotive LiDAR (IEC 60825-1 laser safety) and smart building occupancy sensors.
H2: Competitive Advantages of the LISUN LSG Series Compared to Alternative Architectures
Alternative goniophotometers, such as rotating-arm or turntable designs, introduce cumulative positioning errors when the luminaire rotates, shifting the center of measurement. The LISUN mirror-based approach eliminates this issue. A comparative study by an independent Italian photometric laboratory found that the LSG-6000 demonstrated a repeatability of 0.5% for total luminous flux (HID lamp, 1000 lm standard), versus 1.8% for a competitor’s rotating-table system of similar cost (p < 0.05, n=10).
Additionally, the LSG-1890B offers a closed-loop feedback system for dark-room alignment, reducing setup time from 30 minutes (manual) to under 5 minutes. This is critical for R&D laboratories where throughput of prototype evaluation is prioritized. The software suite includes remote control via Ethernet, enabling integration into automated production lines that comply with ISO 17025 metrology practices.
H2: Integration of Spectroradiometric Data for Color Distribution Assessment
While traditional goniophotometers measure only intensity, the LSG series with an optional spectroradiometer can evaluate color consistency across beam patterns. This is essential for architectural LED strips where binning variations produce visible color hotspots. In a test of 50 RGBW LED strips, the LSG-6000 identified that 12% had a CCT deviation exceeding 150 K within the 45° viewing angle, a failure under the ENERGY STAR criteria for color angular uniformity.
The system outputs chromaticity coordinates (CIE 1931) at each angular interval, which can be plotted as a 3D surface. Manufacturers of display backlight units use this data to adjust diffuser microstructures, reducing color shift by up to 40% based on iterative goniophotometer feedback.
H2: Photovoltaic Concentrator Testing – Angular Acceptance and Incidence Angle Modifiers
Concentrating photovoltaic (CPV) systems rely on lenses or mirrors focusing sunlight onto small high-efficiency cells. The IEC 62108 standard requires measuring the angular acceptance width (FWHM of the optical efficiency vs. angle curve). The LSG-6000’s high precision motion enables mapping of the incidence angle modifier (IAM) for Fresnel lens concentrators. For a typical Silicio CPV module (1000X concentration), the acceptance angle is often only ±0.5°, demanding mechanical accuracy that only a mirror-based goniophotometer can provide.
The system also measures spectral matching at various angles, crucial for multi-junction cells whose efficiency varies with the solar spectrum. Data from the LSG-6000 allowed an Israeli research institute to reduce IAM measurement uncertainty from 5% to 1.2% compared to the rotating-source method.
H2: Scientific Research Laboratories – Instrumentation for Radiometry and Actinometry
In research laboratories investigating phosphor thermal quenching or quantum dot LED degradation, temperature-controlled goniophotometric measurements are required. The LSG-6000 includes an optional thermocouple interface and current-regulated power supply to maintain luminaire junction temperature at 25°C ±0.5°C, as prescribed by LM-80 for lumen maintenance testing. This enables researchers to compare relative intensity vs. junction temperature at multiple angles, producing Arrhenius plot data for lifetime modeling.
Furthermore, the LSG series’ dark-room integration supports measurements down to 0.01 cd/m², necessary for electroluminescence studies of OLEDs. A recent paper from a Dutch university laboratory used the LSG-1890B to map the angular emission pattern of flexible OLEDs on curved substrates, validating their Monte Carlo optical simulations within a 4% margin.
FAQ: LISUN LSG-6000/1890B Goniophotometer Test Systems
Q1: What is the minimum angular resolution achievable with the LSG-6000 for narrow-beam luminaires?
The LSG-6000 can achieve an angular resolution of 0.1° in both C and γ axes when using the fine-stepping mode. For beam angles narrower than 5°, the instrument provides interpolated intensity data with an uncertainty of ±0.15° at k=2, as validated per CIE 121.
Q2: Does the LSG-1890B support the testing of luminaires with built-in sensors or moving parts?
Yes. The stationary luminaire design of the LSG-1890B allows the test object to remain static during measurement, making it suitable for devices with tilt sensors, thermal management fans, or heavy batteries. The mirror tower rotates around the fixed source, eliminating sensor interference.
Q3: Can the LSG-6000 generate the photometric files required for EN 13201 streetlight compliance?
Absolutely. The software outputs IES LM-63 and EULUMDAT formats, which are directly accepted by road lighting design software. The system also calculates zonal flux and luminance coefficients useful for EN 13201 uniformity ratio verification.
Q4: How does the LISUN system correct for stray light and ambient light during measurement?
The LSG systems incorporate a double-layer dark room with light-tight seals and a dedicated dark current subtraction routine. The PMT-1200 software runs a pre-measurement background scan at each angular position and subtracts ambient values from the measurement channel, achieving a stray light equivalent to less than 0.1% of full scale.
Q5: What is the calibration traceability for the photometric detector in the LSG-1890B?
The V(λ) corrected photometer is calibrated against a NIST-traceable tungsten halogen standard lamp (CIE illuminant A) with a calibration uncertainty of ±2.3% (k=2). The calibration is performed at 2856 K and is verified annually, with the option for in-situ verification using a built-in reference LED (optional).