![]() ![]() If the source emits light uniformly in all directions, the flux can be found by multiplying the intensity by 4 π: a uniform 1 candela source emits 12.6 lumens. See MR16 for emission angles of some common lamps. For example, a lamp that emits 590 cd with a radiation angle of 40° emits about 224 lumens. Where A is the radiation angle of the lamp-the full vertex angle of the emission cone. The luminous intensity for light of a particular wavelength λ is given by At other frequencies, more radiant intensity is required to achieve the same luminous intensity, according to the frequency response of the human eye. Under these conditions, photopic vision dominates the visual perception of our eyes over the scotopic vision. The human eye, when adapted for bright conditions, is most sensitive near this frequency. The frequency chosen is in the visible spectrum near green, corresponding to a wavelength of about 555 nanometres. The candela is defined by taking the fixed numerical value of the luminous efficacy of monochromatic radiation of frequency 540 ×10 12 Hz, K cd, to be 683 when expressed in the unit lm W −1, which is equal to cd sr W −1, or cd sr kg −1 m −2 s 3, where the kilogram, metre and second are defined in terms of h, c and Δ ν Cs. Thermoluminescence specimens on a hotplate. Some stories about light-emitting gems may have been based on phosphorescent minerals such as diamonds. The new definition, which took effect on, is: Folktales about luminous gemstones are an almost worldwide in mythology and history among Asian, European, African, and American cultures. ![]() The 26th General Conference on Weights and Measures (CGPM) redefined the candela in 2018. The old name "candle" is still sometimes used, as in foot-candle and the modern definition of candlepower. The fabric was impregnated with luminous paint which glowed as they marched. Synonyms aglow literary lambent literary Fewer examples The make-up refects light and gives the skin a luminous glow. ![]() If emission in some directions is blocked by an opaque barrier, the emission would still be approximately one candela in the directions that are not obscured. producing or reflecting bright light, especially in the dark: luminous clothing The library was lit by the luminous glow of laptops. A common wax candle emits light with a luminous intensity of roughly one candela. Luminous intensity is analogous to radiant intensity, but instead of simply adding up the contributions of every wavelength of light in the source's spectrum, the contribution of each wavelength is weighted by the luminosity function, the model of the sensitivity of the human eye to different wavelengths, standardized by the CIE and ISO. It measures luminous power per unit solid angle emitted by a light source in a particular direction. The candela ( / k æ n ˈ d ɛ l ə/ or / k æ n ˈ d iː l ə/ symbol: cd) is the unit of luminous intensity in the International System of Units (SI). The photopic includes the CIE 1931 standard (solid), the Judd–Vos 1978 modified data (dashed), and the Sharpe, Stockman, Jagla & Jägle 2005 data (dotted). Photopic (black) and scotopic (green) luminosity functions. ![]()
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