Measurements and units

Measurement of ecological light pollution often involves determination of illumination at a given place. Illumination is the amount of light incident per unit area - not the only measurement relevant to ecological light pol? lution, but the most common. Light varies intensity (the number of photons per unit area) and spectral content (expressed wavelength). Ideally, ecologists should mea? sure illumination in photons per square meter per second with associated measurements the wavelengths of light present. More often, illumination is measured in lux (or footcan- dles, the non-SI unit), which expresses the eye. The lux measurement places more emphasis wavelengths of light that the human eye detects best less on those that humans perceive poorly. Because organisms perceive light differently - including wave? lengths not visible to humans - future research on ecolog? ical light pollution should identify these responses measure light accordingly. For example, Gal et al. calculated the response curve of mysid shrimp to and reported illumination in lux adjusted for the spectral sensitivity of the species.