Broadly both measure optical energy, but by convention: a light power meter leans toward measuring the source's output power (often in mW), while an irradiance meter / radiometer leans toward measuring the irradiance received per unit area (often mW/cm² or W/m²). In a photochemical experiment, what actually drives the reaction is "the optical power received per square meter / per square centimeter at the sample surface"—that is, irradiance.
The "center irradiance" rated by the source is often not what the sample actually receives. After reflection, absorption, homogenization, and light guiding, the irradiance at the sample position changes. Citing only the rated value is like using "lamp-mouth brightness" instead of "reaction-site brightness"—the data cannot be reproduced. The correct approach is to place the light power meter probe at the catalyst / electrode's true position.
Perfectlight's PL-MW2000 light power meter is the supporting instrument designed for exactly this kind of sample-position measurement.
Record the probe model, measurement position (center / grid points), unit (mW/cm²), and whether dark current was subtracted; for large-area experiments report non-uniformity. Writing these into the methods section significantly reduces reviewer questions.
Contact Perfectlight: Always asked "how did you calibrate the light intensity?" Tell us your experimental configuration, and Perfectlight will recommend a suitable light power / irradiance meter and calibration plan.
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The power meter leans toward source output power; the irradiance meter/radiometer leans toward received power per unit area (mW/cm²). What actually drives the reaction is the latter.
After reflection, absorption, homogenization, and guiding, sample-position irradiance differs from the lamp-mouth rating; using only the rating substitutes lamp-mouth brightness for reaction-site brightness.
The denominator of AQY, the driving term of rate constants, and cross-lab comparability all depend on sample-position irradiance.
This article does not constitute a performance commitment; specific technical parameters are subject to the actual product documentation and mutual confirmation.
