Instrument to Measure Wavelength: Handheld Spectroradiometer for On-Site Testing

Abstract:

For a long time, rapid inspection of on-site lighting and light source quality relies on traditional illuminance meters and color temperature meters. These devices can only output macroscopic values of illuminance and color temperature, and cannot restore the spectral power distribution. Thus, they cannot support the evaluation of refined indicators such as color rendering index, peak wavelength and color tolerance. Taking the LISUN LMS-6000 handheld spectroradiometer as the core, this paper systematically elaborates the working principle, key parameters and serialized expansion capability of this type of instrument to measure wavelength. Adopting a long-focus crossed asymmetric CT spectroscopic system, the instrument covers a wavelength range of 380–780 nm with wavelength accuracy of ±0.5 nm. It can acquire full-spectrum data within 380–780 nm in one measurement with an integration time ranging from 0.1 ms to 5 s. Based on the spectrum, dozens of photometric and colorimetric parameters including illuminance, correlated color temperature (CCT), color rendering index (CRI), TM-30 (Rg/Rf), peak wavelength and dominant wavelength can be calculated. It complies with test requirements of CIE-13.3, CIE-177 and GB/T 24826, serving as an ideal portable tool for laboratory quality control and on-site inspection.

1. Introduction

Quality control of light source products, acceptance of lamp energy efficiency and light environment evaluation are ultimately based on spectrum, the fundamental physical quantity. The spectral power distribution (SPD) determines the chromaticity, color rendering, color temperature and peak characteristics of a light source, which acts as an objective basis for judging light source performance. Traditional filter-type illuminance meters only provide weighted illuminance readings without identifying spectral profiles. Although bench-top spectrometers with spectroscopic design deliver high accuracy, they are bulky and require computers and darkrooms, making them difficult to carry for field work. Therefore, the instrument to measure wavelength with both high precision and portability, namely the handheld spectroradiometer, has become an essential tool for quality inspection departments, lighting manufacturers and third-party testing organizations for on-site operations. LISUN LMS-6000 is a handheld CCD spectroradiometer developed to meet such demands. Combined with its structural principle and measured parameters, this paper discusses its application value in portable on-site spectral testing.

2. Overall Structure and Working Principle

LMS-6000 adopts a long-focus crossed asymmetric Czerny-Turner (CT) spectroscopic system. Incident light passes through the slit for collimation, gets dispersed by the grating, and then the CCD array receives full-spectrum signals at one time. Compared with scanning monochromators that measure point by point, this “one exposure, full-spectrum imaging” method shortens the test time to millisecond level, which is especially suitable for on-line inspection and batch sampling.

The instrument is equipped with a 5-inch high-definition IPS capacitive touch screen (480×854 resolution). The spectral curve, CIE chromaticity diagram, color tolerance diagram and various parameters can be displayed in real time, so measurement can be completed independently without connecting to a computer. Meanwhile, it supports communication with computers. Under Windows 7/8/10/11 systems, professional software can be used for data export, report generation and secondary analysis. The whole unit weighs about 0.3 kg with dimensions of 135 mm × 80 mm × 23 mm. It is equipped with a 4000 mAh rechargeable lithium battery, supporting up to 20 hours of continuous operation to satisfy long-time outdoor work.

3. Key Performance Parameters of the Instrument to Measure Wavelength

As a kind of instrument to measure wavelength, the core advantages of LMS-6000 lie in wavelength accuracy, dynamic range and stray light suppression, as shown in Table 1.

Table 1 Core Spectral and Photometric Performance Parameters of LMS-6000

As shown in Table 1, its illuminance dynamic range covers six orders of magnitude, enabling direct measurement from dim environment of 0.1 lx to high-brightness light sources up to 500,000 lx. The wavelength accuracy of ±0.5 nm can reliably locate peak wavelength and dominant wavelength. Chromaticity precision of ±0.005 meets acceptance judgment requirements for lamp chromaticity coordinates, while stray light as low as 0.015% ensures authentic restoration of spectra in dark response regions.

LMS-6000 Portable CCD Spectroradiometer

4. Serial Version Expansion

To cater to demands from different industries, the LMS-6000 series covers ultraviolet, visible and near-infrared bands. Users can select models according to the wavelength range of test objects and additional indicators, as shown in Table 2.

Table 2 LMS-6000 Series Models and Wavelength Coverage

It can be seen from Table 2 that the UV variant extends the detection lower limit of this instrument to measure wavelength to the ultraviolet region of 200 nm, and the horticulture lighting version expands the upper boundary to near-infrared band at 950 nm. Equipped with optional functional modules, one single device can support field tests in multiple scenarios such as UV curing, plant supplementary lighting, film lighting and photobiological safety screening.

5. Application Scenarios and Standard Compliance

LMS-6000 is widely used in R&D sampling inspection of LED light sources, factory quality inspection of lamps, acceptance of road and venue lighting, white balance calibration of display screens, light formula verification for horticulture lighting and photobiological safety screening. The test results comply with CIE-13.3 Method of measuring and specifying colour rendering properties of light sources, CIE-177 Colour rendering of white LED light sources, IEEE 1789 recommended practice for modulating current in high-brightness LEDs, and support the measurement of indicators specified in GB/T 24826-2016 national standard. It can be adopted for internal quality judgment of enterprises. For official reports with third-party validity, detailed test data shall be submitted to ILAC-MRA accredited laboratories for verification.

6. Conclusion

The core of portable on-site spectral testing lies in whether an instrument to measure wavelength can stably restore spectral distribution and output reliable photometric and colorimetric parameters without laboratory conditions. With CT spectroscopic architecture and CCD array detector, LISUN LMS-6000 realizes full-spectrum acquisition in one exposure. It achieves ±0.5 nm wavelength accuracy and six-order illuminance dynamic range within 380–780 nm. Through 11 serialized variants, its detectable wavelength band is extended to 200–950 nm. Practical tests and engineering applications prove that its precision and portability satisfy both laboratory quality control and on-site inspection requirements. It is a cost-effective solution replacing traditional illuminance meters and upgrading field detection to spectral-level measurement.