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Light Intensity
Published in Abdul Al-Azzawi, Light and Optics, 2018
The luminous flux F emitted by a light source describes the total amount of visible light that it emits. A small bright source may give off less light than a large diameter source, just as a small hot object may give off less heat than a large warm one. The unit of luminous flux is the lumen lm. Consider a 1-candela light source at the centre of the sphere, as shown in Figure 5.3. Such a light source is referred to as isotropic because it radiates equally in all directions. One lm equals the luminous flux falling on each square metre of a 1 m radius sphere. A lumen of flux is equivalent to about 0.0015 W of yellow–green light of wavelength 555 nm. Since the area of a sphere of radius Ris 4πR2, the above sphere has a total surface area of 4π m2, and the total luminous flux radiated by a 1-cd source is thus 4π lm.
Fibre Optic Lighting
Published in Abdul Al-Azzawi, Photonics, 2017
The study of the measurement of light is called photometry. Two important measurable quantities in photometry are the luminous flux (I), or the light output, and the illumination of a surface (E). Luminous flux measures the brightness of a light source, and it is defined as the total quantity of light emitted per second by a light source. The quantity of light emitted varies with the wavelength, reaching a maximum at the wavelength of 555 nm. The unit for luminous flux (I) is the candle or candela (cd). The early use of certain candles for standards of intensity led to the name of this unit. Currently, a platinum source is used at a specific temperature as the standard for comparison. Another unit, the lumen (lm), is often used to measure the flux of a light source; one candle produces 4π lumens. The lumen is defined as the luminous flux associated with a radiant flux of 1683 W at the wavelength of 555 nm in air. Lumens are equal to the quantity of light emitted by a lamp.
Fibre Optic Lighting
Published in Abdul Al-Azzawi, Fibre Optics, 2017
The study of the measurement of light is called photometry. Two important measurable quantities in photometry are the luminous flux (I), or the light output, and the illumination of a surface (E). Luminous flux measures the brightness of a light source, and it is defined as the total quantity of light emitted per second by a light source. The quantity of light emitted varies with the wavelength, reaching a maximum at the wavelength of 555 nm. The unit for luminous flux (I) is the candle or candela (cd). The early use of certain candles for standards of intensity led to the name of this unit. Currently, a platinum source is used at a specific temperature as the standard for comparison. Another unit, the lumen (lm), is often used to measure the flux of a light source; one candle produces 4π lumens. The lumen is defined as the luminous flux associated with a radiant flux of 1683 W at the wavelength of 555 nm in air. Lumens are equal to the quantity of light emitted by a lamp.
A common type of commercially available LED light source allows for colour discrimination performance at a level comparable to halogen lighting
Published in Ergonomics, 2019
Sara Königs, Susanne Mayr, Axel Buchner
Light sources based on light emitting diodes (LEDs) have become superior to other conventional light sources such as incandescent, halogen, or fluorescent lamps in terms of lifetime and efficiency (Chang et al. 2012). The efficiency of a light source is characterised by its luminous efficacy which is defined as the ratio of the luminous flux to the electrical power consumption (Boyce 2014), measured in lumens per watt (lm/W). Apart from luminous efficacy and lifetime, LED-based light sources differ from other conventional light sources in their spectral power distribution. The spectral power distribution reflects the intensity of emitted radiation at each wavelength (Houser et al. 2016). Radiation in the wavelength range from 380 to 780 nm (the visible spectrum) leads to a response of the human visual system (Boyce 2014) and thus triggers the perception of colour; for normal observers short wavelengths appear as blue light, medium wavelengths as green light, and long wavelengths as red light (Houser et al. 2016).
Understanding multi-domain compact modeling of light-emitting diodes
Published in Cogent Engineering, 2021
Some of the key OET parameters which need to be included in the MCMs are listed in Table 1. Whether a parameter is an input or output depends on the context of measurement or analysis. For example, junction temperature and forward current would determine the forward voltage in electrical model of an LED. Luminous flux is the basic photometric parameter for any light source that measures the amount of emitted radiation perceived by the human eye, hence it needs to be addressed accurately in a multi-domain model of an LED.
A Note on the Use of Uranine Tracer to Visualize Radionuclide Migration Experiments: Some Observations and Problems
Published in Nuclear Technology, 2019
Helen Winberg-Wang, Ivars Neretnieks, Mikko Voutilainen
The temperature in the laboratory was around 20°C, and the light intensity of the light screen behind the slot is around 2000 lm/m2 with daylight color temperature. The entity lm (lumen) is the SI unit of luminous flux. Points on the slot receive around 1500 lm/m2 as some of the light passes outside the slot. The light board was the main source of illumination in the laboratory and the only illumination when the laboratory was not in use.