Luminous definition3/22/2023 ![]() ![]() Photon efficacy in this book is defined as the Photosynthetic Photon Efficacy (PPE), which is the ratio of photosynthetic photon flux to power with the unit of μmol photons s –1 per watt (μmol s –1/w). For a light composed of multiwavelength, it's efficacy is always smaller than 683 lm/w. In this section of the book, we will use the second as the definition of luminous efficacy so as to express how much of the consumed power can be converted into visible light. The second uses the total power consumed by the source, either electric, chemical, or other forms, as the “power.” This is also called luminous efficacy of a source and the maximum possible value of it is smaller than 683 lm/w. This is also called luminous efficacy of radiation and the maximum possible value of it is 683 lm/w for the monochromatic light at a wavelength of 555 nm. ![]() The first is given in Section 2.1.3.1 in which the power is the total radiation from the source. According to how the power is measured, there are two different definitions for it. It is the ratio of luminous flux to power, measured in lumens per watt (lm/w) in the International System of Units (SI). Luminous efficacy is a measure of how well a light source produces visible light. Yong Xu, in Plant Factory Using Artificial Light, 2019 2.1.6.1 Luminous Efficacy, Photon Efficacy, and Light Efficiency For a T12 fluorescent tube with magnetic ballast, the values are 60 lm W −1 (9%), and for 9–32 W compact fluorescent, the values are 46–75 lm W −1 and 8–11.45%. The luminous efficiencies of their respective light sources are 2%, 7% and 14%. An ideal monochromatic 555 nm source has a luminous efficacy of 683 lm W −1 and a luminous efficiency of 100%.Ī typical tungsten light bulb at 2800 K, an ideal black-body radiator at 4000 K, and an ideal black-body radiator at 7000 K have luminous efficacies of 15, 47.5 and 95 lm W −1 respectively. The distinction between efficacy and efficiency is not always carefully maintained in published sources. A common choice is to choose units such that the maximum possible efficacy, 683 lm W −1, corresponds to an efficiency of 100%. In this case, it is often instead called luminous efficiency and may be expressed as a percentage. The luminous efficacy of radiation is then dimensionless. In some systems of units, luminous flux has the same units as radiant flux. The luminous coefficient is luminous efficiency expressed as a value between zero and one, with one corresponding to an efficacy of 683 lm W −1. The lamp efficacy will be 26 and 73 lm W −1, when the whole light is emitted at 450 and 650 nm respectively. If the lamp emits all radiation at 555 nm (where V λ = 1), the luminous efficacy will be of about 680 lm W −1, the theoretical maximum value. Where, V λ = Photopic luminosity or our eyes’ sensitivity function and λ varies from 380 to 700 nm. Luminous Efficacy, K = Luminous Flux F in Lumens Radiant Flux P in Watts = ∫ P λ V λ d λ ∫ P λ d λ ![]()
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