Human eye sensitivity and photometric quantities

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Human eye sensitivity and photometric quantities ( human-eye-sensitivity-and-photometric-quantities )

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16 Human eye sensitivity and photometric quantities Table 16.5. Colors and associated typical LED peak wavelength ranges Color Ultraviolet Violet Blue Cyan Green Wavelength < 390 nm 390–455 nm 455–490 nm 490–515 nm 515–570 nm Color Yellow Amber Orange Red Infrared Wavelength 570–600 nm 590–600 nm 600–625 nm 625–720 nm > 720 nm . 16.5 Luminous efficacy and luminous efficiency The luminous flux, Φlum, is obtained from the radiometric light power using the equation Φlum = 683 lm ∫λ V (λ) P(λ) dλ (16.1) W where P(λ) is the power spectral density, i.e. the light power emitted per unit wavelength, and the prefactor 683 lm/W is a normalization factor. The optical power emitted by a light source is then given by P = ∫λ P(λ) dλ . (16.2) High-performance single-chip visible-spectrum LEDs can have a luminous flux of about 10– 100 lm at an injection current of 100–1 000 mA. The luminous efficacy of optical radiation (also called the luminosity function), measured in units of lumens per watt of optical power, is the conversion efficiency from optical power to luminous flux. The luminous efficacy is defined as Φlum⎡lm ⎤⎡⎤ Luminous efficacy = P = ⎢⎣683 W ∫λ V (λ) P(λ) dλ⎥⎦ ⎢⎣∫λ P(λ) dλ⎥⎦ . (16.3) For strictly monochromatic light sources (Δλ → 0), the luminous efficacy is equal to the eye sensitivity function V(λ) multiplied by 683 lm/W. However, for multicolor light sources and especially for white light sources, the luminous efficacy needs to be calculated by integration over all wavelengths. The luminous efficacy is shown on the right-hand ordinate of Fig. 16.4. The luminous efficiency of a light source, also measured in units of lm/W, is the luminous 284

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