Читать книгу Patty's Industrial Hygiene, Physical and Biological Agents - Группа авторов - Страница 100

A number of specialized terms and units are used to describe temporal and spatial aspects of energy transfer in the form of optical radiation (8). Radiometric units are based on the measures of energy or power without predefined spectral weighting. The Système Internationale (SI) unit of energy is joule (J). Power is the temporal rate of energy transfer. The SI unit of power is watt (W) (1 W = 1 J s⁻¹). Photometric units are measures of visible radiation in which the power at each wavelength is weighted by the photopic luminous efficiency at that wavelength. The photopic luminous efficiency is a standard spectral response function defined by the CIE in 1924 to represent the relative response of the light‐adapted human eye to different wavelengths of visible light. The photopic luminous efficiency curve is illustrated in Figure 2. The photometric equivalent of the radiant power is the luminous flux, measured in SI units of lumens (lms). For monochromatic radiation at 555 nm, which is the maximum of the photopic response function, 1 W of radiant power is equivalent to 683 lm of luminous flux. At other wavelengths, 1 W is equivalent to 683 lm multiplied by the photopic luminous efficiency at that wavelength.

FIGURE 2 Photopic luminous efficiency function, representing the relative sensitivity of the human eye to different wavelengths of light.