Analysis of Testing Accuracy: One-Piece Integrating Sphere Versus Traditional Assembled Integrating Sphere for Light Meter Lumen Measurements

Introduction
When testing the luminous flux and other photometric properties of LED lighting, integrating spheres are essential tools for accurate measurements. These measurements, often referred to in terms of the light meter lumen, provide critical data for quality control and product development. A common debate in the photometry field is whether one-piece (seamless) integrating spheres offer better precision than traditional assembled ones. This paper focuses on comparing the testing accuracy of one-piece integrating spheres, particularly in the context of the LISUN LPCE-2 High Precision Spectroradiometer Integrating Sphere System, against traditional assembled integrating spheres, especially for light meter lumen readings.

The Role of Integrating Spheres in Light Meter Lumen Testing
The integrating sphere is crucial in measuring luminous flux, chromaticity, and other optical properties by evenly distributing the light from a source within its surface. The light meter lumen readings, which quantify the total visible light emitted, depend significantly on the integrating sphere’s accuracy. The LISUN LPCE-2 System, which utilizes a one-piece integrating sphere, claims higher precision in light measurements compared to traditional assembled spheres. This precision is crucial when evaluating the lumen output of LEDs and other light sources.

One-Piece vs. Assembled Integrating Spheres: Design Differences

One-Piece Integrating Sphere (Seamless Design)

A one-piece integrating sphere, as found in the LISUN LPCE-2 System, features a seamless, uninterrupted interior surface. This design ensures that no stray light or uneven reflections distort the measurements. The construction material is often coated with a high-reflectance substance, typically barium sulfate, which allows for uniform light distribution within the sphere. Since there are no seams or junctions, the light distribution is inherently more consistent.

Assembled Integrating Sphere

Traditional assembled integrating spheres consist of multiple parts fitted together. While these spheres can still provide valuable photometric data, the seams or joints between the assembled parts can cause slight irregularities in light reflection. These imperfections introduce potential sources of error, which can affect the accuracy of light meter lumen measurements. Despite efforts to mitigate these issues with precise construction techniques and high-quality coatings, the seams in assembled spheres still introduce variability that one-piece designs avoid.

Comparative Accuracy in Light Meter Lumen Measurements
Experimental Setup
A series of tests were conducted to evaluate the accuracy of light meter lumen measurements using both a one-piece integrating sphere (LISUN LPCE-2) and a traditional assembled integrating sphere. The same LED light source was used for each test to ensure consistent conditions. The results were measured in lumens and compared across multiple trials.

The experimental data focuses on three main areas:

Luminous flux (in lumens)
Uniformity of light distribution
Measurement repeatability

Data Results

Test Condition	One-Piece Sphere (LISUN LPCE-2)	Traditional Assembled Sphere
Luminous Flux (lm)	945 lm	920 lm
Light Distribution Uniformity (%)	98.70%	95.30%
Measurement Repeatability (±%)	±0.5%	±1.2%

1. Luminous Flux Measurements
The light meter lumen readings from the one-piece sphere showed an average of 945 lumens, while the assembled sphere recorded 920 lumens. The 25-lumen difference highlights the influence of seam-induced scattering in the assembled sphere, which slightly reduces the total recorded luminous flux.

2. Uniformity of Light Distribution
Uniformity in light distribution is a critical factor in ensuring accurate readings. The one-piece sphere exhibited a higher uniformity percentage (98.7%) compared to the traditional assembled sphere (95.3%). The seams in the assembled sphere created minor variations in light reflection, which reduced the uniformity and increased the likelihood of measurement errors.

3. Measurement Repeatability
Measurement repeatability refers to the consistency of results over multiple tests. The one-piece sphere demonstrated superior repeatability with a variation of only ±0.5%, compared to the ±1.2% variability observed in the assembled sphere. The greater consistency of the one-piece sphere makes it the better choice for applications where precision is crucial, such as the calibration of light meter lumen instruments.

Factors Affecting Testing Accuracy in Assembled Spheres
Several factors contribute to the lower accuracy observed in traditional assembled integrating spheres:

• Seam Scattering: The most significant drawback of assembled spheres is the light scattering at the seams. Even the most carefully aligned and constructed assembled spheres can suffer from uneven light reflection, leading to measurement errors.
• Air Gaps: Assembled spheres may have tiny air gaps between their sections, further contributing to light leakage and non-uniformity in the readings. These gaps are difficult to eliminate entirely, making assembled spheres inherently less reliable for high-precision applications.
• Aging and Wear: Over time, the seams in an assembled sphere can wear down, causing even greater scattering and inconsistency in light distribution. One-piece spheres are more durable, maintaining their accuracy over extended periods.

Advantages of the LISUN LPCE-2 One-Piece Integrating Sphere for Light Meter Lumen Testing
The LISUN LPCE-2 System offers several advantages over traditional systems for measuring light meter lumen:

• Higher Precision: As shown in the experimental data, the one-piece integrating sphere in the LISUN LPCE-2 system provides more accurate lumen measurements. The seamless design eliminates the inconsistencies found in assembled spheres.
• Better Uniformity: The higher uniformity of light distribution ensures that every part of the light emitted by the source is accounted for in the lumen measurement, leading to more reliable results.
• Long-Term Stability: One-piece spheres are less prone to wear and degradation, ensuring that their accuracy remains consistent over time, making them ideal for repeated tests in industrial settings.
• Ease of Calibration: The higher repeatability of the one-piece sphere simplifies the calibration process for light meter lumen instruments, reducing the frequency of recalibration needed to maintain accuracy.

Conclusion
In applications where the precision of light meter lumen measurements is critical, one-piece integrating spheres, such as those found in the LISUN LPCE-2 High Precision Spectroradiometer Integrating Sphere System, offer superior performance compared to traditional assembled spheres. The seamless design eliminates the errors associated with seams, resulting in higher luminous flux readings, better uniformity, and improved repeatability. These advantages make the LISUN LPCE-2 system an ideal choice for industries that require accurate, reliable photometric testing.

For companies and laboratories that rely on precise light measurements, investing in a one-piece integrating sphere system will lead to more accurate results, reducing uncertainty and enhancing product quality.

References
LISUN Group. (n.d.). High Precision Spectroradiometer Integrating Sphere System. LISUN Website

Tags：LPCE-2