An In-Depth Analysis of the Working Principles and Measurement Logic of Light Power Meters

In research on photocatalytic hydrogen (H₂) production, carbon dioxide (CO₂) reduction, and solar cells, the accurate measurement of light radiation intensity is a key prerequisite for calculating quantum efficiency and energy conversion efficiency. As the “second pair of eyes” for researchers, light power meters can capture invisible photon energy and convert it into quantifiable electrical signals. To ensure the accuracy and reproducibility of experimental data, understanding the underlying detection principles and physical mechanisms is crucial for proper instrument selection.

From a physical perspective, light power meters are mainly based on two core detection principles: the photoelectric effect and the photothermal effect.

The first is the photoelectric detection principle based on semiconductor materials, which primarily utilizes the photovoltaic effect to directly convert photons into electrical current. When light of a specific wavelength irradiates the semiconductor PN junction of a detector, if the photon energy exceeds the bandgap of the material, electron–hole pairs are generated and, under the action of the internal electric field, form a photocurrent. This detection method features extremely fast response and high sensitivity. For example, the FZ-A domestic irradiance meter is a typical application of this principle. It adopts a high-precision, low-power digital chip, and its detector undergoes rigorous spectral and angular response calibration. Due to the selective spectral response of semiconductor materials, the FZ-A is specifically calibrated for the visible light range from 400 nm to 1000 nm, making it particularly suitable for measuring light source intensity close to the AM 1.5G standard solar spectrum.

The second is the photothermal detection principle based on a thermopile. The photosensitive surface of the detector is typically coated with a black layer possessing extremely high absorptivity. When light irradiates the surface, optical energy is converted into thermal energy, leading to a temperature rise on the detector surface. This temperature increase is then converted into a voltage signal via the thermoelectric electromotive force generated by a series of thermocouples (thermopile). The greatest advantage of thermal detectors lies in their exceptionally flat spectral response, which can cover a broad range from ultraviolet to far-infrared. The PL-MW2000 high-power light power meter is a professional device designed based on this principle. It covers a spectral range from 200 nm to 11000 nm, with a maximum measurement range of up to 20 W. To cope with the enormous energy impact generated by high-power light sources (such as a 300 W xenon lamp), this device is also equipped with a unique detachable optical attenuator: when the optical power exceeds 5 W, physical attenuation is achieved by installing the attenuator, thereby protecting the detection core and ensuring accurate readings under high-power conditions.

In addition to detection principles, a scientific measurement procedure is equally critical for obtaining accurate data.

In practical research scenarios, the power density distribution of light spots produced by xenon lamp sources is often non-uniform, with the central region typically exhibiting higher intensity than the edges. Measuring only the central point can therefore lead to overestimated conversion efficiencies. As a result, researchers usually employ the PLS-FTC five-point method light power density measurement assembly for multi-point sampling. Through its sliding-slot design, this assembly enables rapid positioning of the center and four symmetric edge points of the light spot, followed by calculation of the average irradiance using a specific formula. This rigorous measurement protocol effectively avoids errors caused by non-uniform light fields, ensuring that the obtained data truly reflect the energy input on the illuminated surface of the catalytic reactor.

In essence, the working principles of light power meters represent an engineering realization of photoelectric and photothermal energy conversion. By appropriately selecting semiconductor-based detectors (such as the FZ-A) or thermopile-based detectors (such as the PL-MW2000), and combining them with standardized multi-point measurement methods, researchers can establish a solid logical link between microscopic chemical reactions and macroscopic optical energy input, thereby driving continuous breakthroughs in new energy technologies.