Energy Efficient House Plan - White LEDs
Energy Efficient House Plan
White LED brought the real revolution in the lighting industry and was made possible with the creation of blue and UV LEDs. By nature of semiconductors, there is no unique band gap that can emit white light. In order to generate white light from LEDs two main processes are used in inorganic LEDs: wavelength mixing and wavelength conversion. White LEDs made from wavelength mixing are based on three colors; Red, Green and Blue are mixed. This technique presents the advantage of offering the control of the tone of the white light by changing the proportion of the different colors.
In the phosphor-based white LEDs the process is based on wavelength conversion due to the photoluminescent properties of phosphor. In general white light is made from blue or near-ultraviolet LED whose radiation is absorbed by a phosphor-coated surface before being reemitted in a white color similar to fluorescent lights. The phosphor can be deposited on the LED die directly or on the plastic housing.
Generally, commercially available white LEDs are based on InGaN blue LEDs coated with a cerium (Ce) doped yttrium aluminum garnet (YAG) phosphor, YAG:Ce. In order to use LEDs for general lighting and make them good replacements for incandescent and fluorescent lamps, the most important requirement that LEDs should fulfill besides efficiency and life span, is a good color rendering. Good color rendering of LEDs should be combined with their good power efficiency. In the very first white LED, a 5 mm package, the phosphor was dispersed within an epoxy resin that surrounded the blue LED die.
The main difference between a blue and a similar white LED is the phosphor dispersed within the epoxy surrounding the die or over the die itself. The color of LED lamps is completely controlled by the selection of the appropriate phosphors, giving the required control over the lamp color for many general illumination applications. However, achieving this goal will require optimization of all aspects of white LED lamps including the phosphor efficiency.
The efficacy of solid-state lighting based upon InGaN LEDs has improved by more than ten times over the last decade: the efficacy of cool white LEDs can surpass those of linear fluorescent lamps (more than 100 lm/W) and warm white LED 1 W LEDs surpass compact fluorescent lamp efficacies (more than 50–80 lm/W). For 2015, the US department of Energy plans the efficacy of warm white packages to reach 138 lm/W; this will be a significant technical achievement that would lead to a greater market penetration of solid-state lighting. As may be expected, the inclusion of a small amount of red phosphor with YAG:Ce improved the CRI to acceptable range (a color rendering index higher than 80) and increased the light conversion. The phosphors and phosphor blends of interest have excitation frequencies in the desired range of near-UV and blue (380–450 nm) and emit in bands across the visible spectrum.
Temperature Deterioration and Aging of LEDs
The reliability of a lighting system is in the lumen power maintenance and color variation minimization. As the market of white high brightness LEDs is continuously growing, LEDs with several watts of input electric power are available. This makes them ideal candidates to replace classic lighting systems. The self-heating of these devices is also increasing with the power input.
In contrast to incandescent and fluorescent lights the heat generated in an LED is not radiated as part of the its monochromatic spectrum. One of the weak points of LEDs is the necessity of heat management. Overheat of an LED will result in junction deterioration, the epoxy color changing and deterioration leading to transmittance reduction and refractive index variation of the phosphor. The consequences are a lower lumen output and the modification of spectral properties (color); in other words lower brightness and color variation. A microscopic analysis shows that the effects of temperature stress on the LED packaging is the carbonization of the plastic package of the device.
To maintain the high light output of an LED and ensure a long life span, it is necessary to efficiently evacuate the heat. Incandescent light bulbs convert about 8% of the input electric power into visible light, and the rest is radiated in the form of heat. For fluorescent lights the ratio is about 21% of the input electric power that is converted into light and the rest into heat. For LEDs, 15–25% of the input electric power is turned into light, the rest heats up the device itself and needs to be effectively evacuated.
LED Lamps
LED chips can be made with light efficacy reaching 100 lm/W, equivalent of fluorescent lamps and their efficiency 80% better than incandescent light bulbs. LED chips can be associated in different forms to make lamps in order to replace different household lamps with different type of bases as halogen lamps, incandescent lights, compact fluorescent light bulbs and fluorescent light tubes. Lamps made from LEDs are equipped with electronic circuitry in order to turn the AC voltage to DC. Also, there is a heat evacuation system to avoid high heat that would destroy the lamp. LED lamps are generally made in different levels of color correlated temperature from cool white 6,400 K to warm white 2,700 K. If you find this post useful, please share it with your friends. To find out more, you can check out Energy Efficient House Plan.
White LED brought the real revolution in the lighting industry and was made possible with the creation of blue and UV LEDs. By nature of semiconductors, there is no unique band gap that can emit white light. In order to generate white light from LEDs two main processes are used in inorganic LEDs: wavelength mixing and wavelength conversion. White LEDs made from wavelength mixing are based on three colors; Red, Green and Blue are mixed. This technique presents the advantage of offering the control of the tone of the white light by changing the proportion of the different colors.
In the phosphor-based white LEDs the process is based on wavelength conversion due to the photoluminescent properties of phosphor. In general white light is made from blue or near-ultraviolet LED whose radiation is absorbed by a phosphor-coated surface before being reemitted in a white color similar to fluorescent lights. The phosphor can be deposited on the LED die directly or on the plastic housing.
Generally, commercially available white LEDs are based on InGaN blue LEDs coated with a cerium (Ce) doped yttrium aluminum garnet (YAG) phosphor, YAG:Ce. In order to use LEDs for general lighting and make them good replacements for incandescent and fluorescent lamps, the most important requirement that LEDs should fulfill besides efficiency and life span, is a good color rendering. Good color rendering of LEDs should be combined with their good power efficiency. In the very first white LED, a 5 mm package, the phosphor was dispersed within an epoxy resin that surrounded the blue LED die.
The main difference between a blue and a similar white LED is the phosphor dispersed within the epoxy surrounding the die or over the die itself. The color of LED lamps is completely controlled by the selection of the appropriate phosphors, giving the required control over the lamp color for many general illumination applications. However, achieving this goal will require optimization of all aspects of white LED lamps including the phosphor efficiency.
The efficacy of solid-state lighting based upon InGaN LEDs has improved by more than ten times over the last decade: the efficacy of cool white LEDs can surpass those of linear fluorescent lamps (more than 100 lm/W) and warm white LED 1 W LEDs surpass compact fluorescent lamp efficacies (more than 50–80 lm/W). For 2015, the US department of Energy plans the efficacy of warm white packages to reach 138 lm/W; this will be a significant technical achievement that would lead to a greater market penetration of solid-state lighting. As may be expected, the inclusion of a small amount of red phosphor with YAG:Ce improved the CRI to acceptable range (a color rendering index higher than 80) and increased the light conversion. The phosphors and phosphor blends of interest have excitation frequencies in the desired range of near-UV and blue (380–450 nm) and emit in bands across the visible spectrum.
Temperature Deterioration and Aging of LEDs
The reliability of a lighting system is in the lumen power maintenance and color variation minimization. As the market of white high brightness LEDs is continuously growing, LEDs with several watts of input electric power are available. This makes them ideal candidates to replace classic lighting systems. The self-heating of these devices is also increasing with the power input.
In contrast to incandescent and fluorescent lights the heat generated in an LED is not radiated as part of the its monochromatic spectrum. One of the weak points of LEDs is the necessity of heat management. Overheat of an LED will result in junction deterioration, the epoxy color changing and deterioration leading to transmittance reduction and refractive index variation of the phosphor. The consequences are a lower lumen output and the modification of spectral properties (color); in other words lower brightness and color variation. A microscopic analysis shows that the effects of temperature stress on the LED packaging is the carbonization of the plastic package of the device.
To maintain the high light output of an LED and ensure a long life span, it is necessary to efficiently evacuate the heat. Incandescent light bulbs convert about 8% of the input electric power into visible light, and the rest is radiated in the form of heat. For fluorescent lights the ratio is about 21% of the input electric power that is converted into light and the rest into heat. For LEDs, 15–25% of the input electric power is turned into light, the rest heats up the device itself and needs to be effectively evacuated.
LED Lamps
LED chips can be made with light efficacy reaching 100 lm/W, equivalent of fluorescent lamps and their efficiency 80% better than incandescent light bulbs. LED chips can be associated in different forms to make lamps in order to replace different household lamps with different type of bases as halogen lamps, incandescent lights, compact fluorescent light bulbs and fluorescent light tubes. Lamps made from LEDs are equipped with electronic circuitry in order to turn the AC voltage to DC. Also, there is a heat evacuation system to avoid high heat that would destroy the lamp. LED lamps are generally made in different levels of color correlated temperature from cool white 6,400 K to warm white 2,700 K. If you find this post useful, please share it with your friends. To find out more, you can check out Energy Efficient House Plan.
Source...