The Basics of Light Measurement: Radiometry vs Photometry, Units and Conversion

In short Radiometry measures all the radiation – UV, visible and IR – in physical units: watts, W/sr, W/m². Photometry measures light as the eye sees it (about 380–780 nm). It weights the spectrum with the eye’s sensitivity curve V(λ) and reports lumens, candela, lux and cd/m². One factor links them: 683 lm per watt […]
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