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The Optics of LifeA Biologist's Guide to Light in Nature$
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Sönke Johnsen

Print publication date: 2011

Print ISBN-13: 9780691139906

Published to Princeton Scholarship Online: October 2017

DOI: 10.23943/princeton/9780691139906.001.0001

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Units and Geometry

Units and Geometry

(p.8) Chapter Two Units and Geometry
The Optics of Life

Sönke Johnsen

Princeton University Press

This chapter explores units and geometry in light measurement. For biologists not working on humans, it comes down to a few simple rules: use photons not watts; use wavelength not frequency, but be extremely careful when comparing the peaks of light spectra to sensitivity curves; stick to measuring radiance and irradiance, but be a pioneer and add scalar irradiance measurements to your papers; irradiance sometimes obeys the inverse-square law; radiance rarely does; do not use photometric units, except possibly for lux. However, the underlying principle of weighted integrals is useful for modeling animal vision and other wavelength-dependent processes.

Keywords:   units, geometry, light measurement, photons, wavelength, radiance, irradiance, lux, animal vision

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