Introduction to Integrating Sphere Spectroradiometry
Integrating spheres are fundamental instruments in optical metrology, providing uniform light diffusion for accurate photometric and colorimetric measurements. The LISUN LPCE-3 Integrating Sphere Spectroradiometer System is engineered for high-precision testing of luminous flux, chromaticity, and spectral power distribution (SPD) across diverse lighting applications. This system complies with international standards such as CIE 177, CIE-13.3, IES LM-79, and EN13032-1, ensuring reliability in industrial and research environments.
System Architecture and Key Specifications
The LPCE-3 integrates a high-reflectance sphere, precision spectroradiometer, and advanced software for comprehensive light measurement. Key specifications include:
| Parameter | Specification |
|---|---|
| Sphere Diameter | 0.3m, 0.5m, 1m, 1.5m, or 2m (customizable) |
| Spectral Range | 380–780nm (extendable to 200–2500nm) |
| Wavelength Accuracy | ±0.3nm |
| Luminous Flux Range | 0.01–200,000 lm |
| Color Temperature Range | 1,000–100,000K |
| CRI (Ra) Measurement | 0–100 |
| Measurement Uncertainty | <1.5% (luminous flux), <0.002 (Δu’v’) |
The system employs a CCD-based spectroradiometer with high dynamic range and low stray light interference, ensuring repeatability in high-accuracy applications.
Testing Principles and Methodologies
Absolute Luminous Flux Measurement
The LPCE-3 utilizes the 4π geometry method, where the test sample is placed at the sphere’s center. A reference standard lamp calibrates the system, compensating for sphere wall reflectance (typically >95% BaSO₄ coating). The spectroradiometer captures omnidirectional light, integrating spectral data to compute total luminous flux (Φv) via:
[
Φ_v = Km int{380}^{780} V(lambda) cdot S(lambda) , dlambda
]
Where:
- (K_m) = Photopic luminosity factor (683 lm/W)
- (V(lambda)) = CIE standard observer curve
- (S(lambda)) = Spectral power distribution
Chromaticity and CRI Analysis
The system derives CIE 1931 (x,y) and CIE 1976 (u’,v’) chromaticity coordinates, along with metrics like CCT (Correlated Color Temperature) and CRI (Color Rendering Index). For LED manufacturing, deviations in peak wavelength (Δλ) and FWHM (Full Width at Half Maximum) are critical for binning consistency.
Industry Applications
LED and OLED Manufacturing
The LPCE-3 ensures compliance with ANSI C78.377 and IEC 62612 for white LED chromaticity uniformity. Manufacturers use it for:
- Spectral consistency testing in binning processes
- Flicker analysis (IEEE PAR1789) for PWM-driven LEDs
- OLED panel emissive uniformity validation
Automotive Lighting Testing
Automotive headlamps and signal lights must meet ECE R48 and SAE J578 standards. The LPCE-3 evaluates:
- Luminous intensity distribution (via goniophotometer coupling)
- UV/IR spectral leakage in laser-based headlights
Aerospace and Aviation Lighting
Aviation navigation lights require FAA TSO-C96 compliance. The LPCE-3 verifies:
- Chromaticity adherence to ICAO Annex 14
- Luminance stability under thermal cycling (-40°C to +85°C)
Photovoltaic Industry
Solar simulators (IEC 60904-9) rely on spectral match verification. The LPCE-3 quantifies AM1.5G spectrum deviations for PV cell calibration.
Competitive Advantages
- Modular Calibration – Sphere apertures and detector positions are adjustable for near-field (NIST-traceable) and far-field measurements.
- Multi-Standard Compliance – Simultaneous adherence to LM-79 (photometry) and CIE S 025 (LED testing).
- Thermal Compensation – Active cooling stabilizes the spectroradiometer for high-power LED testing (up to 500W).
Case Study: Urban Lighting Design Validation
A municipal lighting project in Berlin utilized the LPCE-3 to validate 4,000 LED streetlights. The system confirmed:
- Luminous flux maintenance >90% after 10,000 hours (TM-21 extrapolation)
- CCT consistency (±50K across batches)
FAQ Section
Q1: How does the LPCE-3 correct for self-absorption in high-power LED testing?
The system employs an auxiliary lamp subtraction method, where a reference measurement without the DUT (Device Under Test) eliminates thermal drift errors.
Q2: Can the LPCE-3 measure pulsed light sources (e.g., strobes)?
Yes, with a minimum pulse width of 10μs and sync input for triggered acquisition (up to 10kHz sampling).
Q3: What is the typical calibration interval for the sphere?
Annual recalibration is recommended, though NIST-traceable sources allow user-side verification via CSL (Calibration Standard Lamp).
Q4: Does the system support multi-channel spectrometer synchronization?
The LPCE-3’s software (LISUN LMS-9000) allows parallel spectrometer arrays for hyperspectral applications.
Q5: How is sphere aging (degradation of BaSO₄ coating) mitigated?
Regular reflectance recalibration (via PTFE standards) and controlled humidity storage (<60% RH) preserve coating integrity.
