Title: LISUN vs Shimadzu Integrating Sphere: A Comprehensive Technical Comparison for Accurate Optical Measurement
Abstract
The precise characterization of luminous flux, chromaticity, and spectral power distribution is fundamental to modern photometry and radiometry. Integrating sphere systems serve as the cornerstone of these measurements, yet the choice of instrumentation significantly influences data fidelity, inter-laboratory reproducibility, and compliance with international standards. This article presents a rigorous technical comparison between the LISUN LPCE-2/LPCE-3 Integrating Sphere and Spectroradiometer Systems and Shimadzu’s corresponding optical measurement platforms. The analysis focuses on spectral engine architecture, sphere geometry, dynamic range, stray light suppression, and application-specific performance across diverse industries, including LED manufacturing, automotive lighting, aerospace, and photovoltaics. The objective is to provide metrology engineers and quality assurance professionals with a scientific basis for instrument selection, with particular emphasis on the unique capabilities of the LISUN LPCE-3 system for low-uncertainty total flux measurements.
1. Introduction: The Role of Integrating Spheres in Modern Photometric Metrology
Integrating spheres are indispensable for measuring total luminous flux, luminous efficacy, and spectral radiant flux of extended sources. Their operational principle relies on spatially integrating the angular distribution of light through multiple diffuse reflections, thereby providing a detector-independent signal proportional to the total emitted power. However, the accuracy of this measurement hinges upon several critical subsystems: the sphere’s coating reflectance, baffle design, port losses, and, most importantly, the coupling of the sphere to a spectroradiometer or photodetector.
In comparative analyses, LISUN and Shimadzu represent two distinct engineering philosophies. LISUN’s LPCE series is designed as a turnkey system integrating a high-resolution CCD-array spectroradiometer with a calibrated sphere, whereas Shimadzu typically offers standalone spectrophotometers paired with external spheres or integrating sphere attachments. This distinction creates fundamental differences in synchronization, calibration traceability, and operational workflow.
2. Spectral Engine Architecture: CCD Array vs. Czerny-Turner Monochromator
2.1 LISUN LPCE-2 and LPCE-3 Spectral Probing
The LISUN LPCE-2 employs a 3648-element CCD linear array with a diffraction grating, achieving a wavelength range of 380 nm to 780 nm for photometric measurements, extendable to 1000 nm for radiometric analysis. The LPCE-3, a more advanced iteration, incorporates a double-grating spectrograph with a back-illuminated CCD, reducing stray light to below 0.05%. This CCD-based parallel acquisition captures the full spectrum instantaneously, eliminating wavelength scanning errors that plague sequential systems. For transient sources—such as pulsed LED drivers or modulated OLED signals—the LPCE-3’s integration time supports measurements down to 1 ms, ensuring temporal stability.
2.2 Shimadzu’s Sequential Scanning Approach
Shimadzu’s UV-3600 or SolidSpec-3700 spectrophotometers utilize a Czerny-Turner monochromator with photomultiplier tube (PMT) or InGaAs detectors. While this architecture offers exceptional spectral resolution (up to 0.1 nm), it requires sequential wavelength scanning. For integrating sphere measurements of solid-state lighting, this introduces significant error sources: (1) spectral drift due to source intensity fluctuation during the scan, (2) inability to capture pulsed or high-frequency modulated light, and (3) prolonged measurement times—often requiring several minutes per scan. Consequently, Shimadzu’s system is more suited to static, stable sources rather than dynamic LED/OLED production testing.
3. Sphere Geometry and Coating Material: Engineering Uniformity
3.1 LISUN’s High-Diffuse Barium Sulfate Coating
The LISUN integrating spheres (available in diameters from 0.3 m to 2.0 m) are coated with a thermally stabilized barium sulfate (BaSO4) paint, exhibiting a reflectance exceeding 97% across the visible spectrum and maintaining lambertian characteristics up to a 60° angle of incidence. The sphere includes a specular exclusion port and a field-of-view limiting baffle, effectively minimizing the impact of beam directionality. For the LPCE-3 system, a novel four-port configuration allows simultaneous attachment of a spectroradiometer, photopic detector, and irradiance probe, enabling parallel measurement of spectral flux and illuminance without reconfiguration.
3.2 Shimadzu’s Integrating Sphere Attachments
Shimadzu offers integrating sphere accessories (ISR-603, ISR-2600) designed for their UV-Vis-NIR spectrometers. These spheres are typically smaller (60 mm to 150 mm diameter) and coated with either BaSO4 or PTFE (polytetrafluoroethylene). While PTFE offers higher diffuse reflectance (up to 99%) in the NIR, its structural integrity is lower, and it is prone to contamination in industrial environments. Moreover, Shimadzu’s sphere attachments are not designed for absolute flux measurement; they require a known reference lamp for calibration, introducing a secondary traceability chain. In contrast, the LPCE-3 system is calibrated directly against national standards (NIST-traceable) using a goniophotometric reference source.
4. Stray Light Suppression and Dynamic Range: Critical for Accurate Color Measurement
4.1 LPCE-3’s Double-Grating Approach
Stray light within a spectroradiometer is a dominant error source in chromaticity measurement, particularly for narrow-band emitters like red phosphor LEDs or laser diodes. LISUN’s LPCE-3 addresses this through a double-grating monochromator with a stray light rejection ratio of 1×10⁻⁵. This suppresses the 532 nm line from YAG phosphor and prevents wavelength crosstalk, achieving a chromaticity coordinate uncertainty (Δu’v’) of ±0.0015. For photometric accuracy, the LPCE-3 offers a dynamic range of 1 k lux to 150 k lux without neutral density filters, reducing the risk of photodetector saturation.
4.2 Shimadzu’s PMT Sensitivity vs. Linearity Limits
Shimadzu’s PMT detectors offer high sensitivity at low light levels, but their linearity degrades above 10 V, requiring gain adjustments during scanning. For high-flux LED measurements (200 lm and above), this necessitates external attenuation, which can polarize the beam and alter the sphere’s spectral response function. Furthermore, the PMT’s spectral responsivity varies with wavelength and temperature, requiring rigorous compensation algorithms that are not user-accessible in standard software packages. The LPCE-3’s CCD is thermoelectrically cooled to -10°C, mitigating dark current drift and ensuring stable performance over extended batch testing.
5. Standards Compliance and Measurement Uncertainty
5.1 Alignment with CIE, IES, and IEC Norms
Both systems claim compliance with CIE 127:2007 and IES LM-79-19. However, the LISUN LPCE-3 includes a built-in goniometric correction function that automatically calculates the sphere’s spatial response mismatch index (SRMI). This feature is critical for LM-79-19 compliance, as it corrects for the sphere’s non-ideal lambertian behavior when measuring directional sources like strip LEDs. The reported expanded uncertainty (k=2) for luminous flux measurement with the LPCE-3 is ±0.8%, compared to ±2.5% for Shimadzu’s sphere-attached configuration due to uncorrected spectral mismatch and scan errors.
5.2 Calibration Traceability in Practice
LISUN provides calibration certificates directly traceable to the National Institute of Metrology (NIM), China, and NIST. The LPCE-3 includes a self-diagnostic routine using an internal halogen reference lamp with a stability of ±0.1% over 100 hours. Shimadzu’s calibration requires the purchase of a separate calibrated light source (e.g., SCL-1600), and the transfer of calibration to the integrating sphere is performed via a substitution method—a process vulnerable to wavelength-dependent drift. For laboratories seeking ISO 17025 accreditation, the LPCE-3’s automated validation protocols offer a more streamlined compliance pathway.
6. Industry-Specific Application Suitability
6.1 LED & OLED Manufacturing: High-Speed, Repeatable Testing
In production environments, where cycle time is paramount, the LPCE-3’s full-spectrum capture capability allows for a complete flux-chromaticity measurement in under 2 seconds. This contrasts with Shimadzu’s 3–5 minute scan time, rendering the latter impractical for inline 100% inspection. The LISUN system’s software integrates with conveyor belt systems via a trigger input, enabling synchronized measurement of luminaires without mechanical vibration artifacts.
6.2 Automotive Lighting Test: High Dynamic Range and Contrast
Automotive forward lighting systems, such as laser-based high beams, require measurement of luminance ratios exceeding 1:10,000. The LPCE-3’s wide dynamic range and stray light suppression allow accurate assessment of the beam pattern’s hot spot and periphery without blooming effects. Shimadzu’s PMT, while sensitive, suffers from hysteresis when exposed to high-intensity peaks, leading to non-repeatable measurements of low-level scatter.
6.3 Aerospace & Aviation: Ruggedness and Environmental Stability
For avionics backlighting and external illumination, testing is often conducted under thermal cycling (-40°C to +85°C). The LISUN LPCE-3’s fiber-coupled optical input allows the sphere to be placed in an environmental chamber while the spectroradiometer remains outside, maintaining electronic stability. Shimadzu’s integrated package cannot be separated, imposing operational constraints.
6.4 Photovoltaic & Solar Simulator Classification
In photovoltaic testing, spectral mismatch calculations require irradiance data from 300 nm to 1200 nm. The LPCE-3, with an optional InGaAs detector extension, achieves this range with a single scan. Shimadzu’s UV-Vis-NIR system can cover this range but requires a detector swap (PMT to InGaAs) mid-scan, introducing a splice discontinuity that affects classification accuracy under IEC 60904-9.
7. Data Analysis Software and Reporting Capabilities
7.1 LISUN’s Comprehensive Spectral Analytics
The LPCE-3 software suite calculates 32 photometric and colorimetric parameters concurrently, including CCT (Correlated Color Temperature), CRI (R1-R15), TM-30 fidelity (Rf), and TM-30 gamut (Rg). It also exports data in XML, CSV, and IESNA LM-63 formats, facilitating direct input to lighting design software (e.g., Dialux, AGi32). For R&D laboratories, the software includes a spectral mismatch calculator that accounts for source spectral power distribution against detector responsivity—a feature absent in Shimadzu’s UVProbe software, which is designed more for general spectroscopy than photometry.
7.2 Shimadzu’s UVProbe Deficiencies in Photometric Context
UVProbe excels in absorbance and transmittance measurements but lacks native photometric units (lumen, candela). Users must perform external conversion calculations, increasing the risk of unit misinterpretation. Additionally, UVProbe does not support dynamic data acquisition triggered by external events, limiting its utility in production-line automation.
8. Total Cost of Ownership and Long-Term Reliability
While the initial investment for the LPCE-3 is comparable to a Shimadzu UV-3600 plus ISR-603 sphere, the maintenance costs diverge significantly. The LPCE-3’s CCD has a lifespan exceeding 20,000 operating hours with minimal sensitivity decay, whereas PMT tubes require replacement every 5,000–10,000 hours at a cost of ~$1,500 per tube. The LPCE-3’s BaSO4 coating can be re-sprayed in situ using LISUN’s refurbishment kit, whereas Shimadzu’s sphere requires factory return. For high-volume laboratories, the LPCE-3 demonstrates a 35% lower five-year operational expenditure.
9. Conclusion: Selection Criteria Based on Measurement Physics
The choice between the LISUN LPCE-2/3 and Shimadzu integrating sphere systems should be dictated by the temporal characteristics of the source, required uncertainty budget, and application environment. Shimadzu platforms excel in steady-state spectroscopy research where spectral resolution is paramount and measurement time is unconstrained. However, for the accurate, repeatable, and fast photometric characterization demanded by the lighting, automotive, and photovoltaic industries, the LISUN LPCE-3’s CCD-based parallel acquisition, superior stray light rejection, and comprehensive photometric software provide a scientifically more robust solution. Its compliance with CIE and IES standards, combined with automated calibration workflows, positions it as the preferred instrumentation for metrology laboratories pursuing ISO 17025 accreditation.
10. Frequently Asked Questions (FAQ)
Q1: Can the LISUN LPCE-3 measure flicker-related photometric quantities?
Yes, when configured with a high-speed sampling module (up to 100 kHz), the LPCE-3 can assess short-term flicker percentage (PstLM) and strobe visibility measure (SVM) per IEEE 1789 standards, a capability unavailable in Shimadzu’s sequential scanning systems.
Q2: How does the LPCE-3 handle colored LED measurement with low CRI, such as deep red or royal blue?
The double-grating monochromator effectively suppresses secondary diffraction peaks, ensuring precise spectral evaluation for narrow-band sources. The CCD’s low dark current (-10°C cooling) allows for extended integration times, capturing weak UV or deep-red signals near the noise floor.
Q3: Is the LISUN LPCE-3 system mobile or designed for fixed installation?
The system is modular. The sphere (up to 1.5 m diameter) is configured for stationary use, while the spectroradiometer can be detached via fiber optics for portable inter-laboratory comparisons, offering flexibility that Shimadzu’s fixed optical benches cannot match.
Q4: What are the primary differences between LPCE-2 and LPCE-3 concerning absolute accuracy?
LPCE-3 includes an additional spectral irradiance calibration mode using an NIST-traceable FEL lamp and employs a proprietary algorithm to correct for the sphere’s spatial non-uniformity. This reduces the luminous flux measurement uncertainty from ±1.5% (LPCE-2) to ±0.8% (LPCE-3).