> Quick answer: A 6500K LED uses a blue pump light with YAG:Ce phosphor, converting it into white light through Stokes shift, emitting yellow-to-red wavelengths. The CCT is tuned by adjusting the phosphor blend [3][18]. Thermodynamic efficiency remains unspecified but involves significant energy losses.
A 6500K LED solar lamp operates on a fascinating principle: blue pump light excites phosphors to emit white light, but how does this conversion happen? This article breaks down the physics and thermodynamics behind it.
How Blue Pump Light Converts to White Light
The process begins with a blue LED chip emitting light in the 440–470 nm range [18][21]. This blue light serves as the pump source, exciting a phosphor layer—typically cerium-doped yttrium aluminum garnet (YAG:Ce)—which fluoresces via Stokes shift. The Stokes shift involves converting absorbed higher-energy photons into lower-energy photons, primarily in the yellow-to-red region [3][13]. This emitted light mixes with unabsorbed blue light to produce a white appearance due to spectral mixing [7][17].
For 6500K LEDs, which provide a „cool white” or „daylight” color temperature, the phosphor composition is tuned to emit less yellow and more green-to-red components. This adjustment ensures that the spectrum aligns with higher CCT values by balancing the light output towards blues [7][13]. The chromaticity coordinates for 6500K typically fall around (0.3, 0.3) on the CIE 1931 diagram [18][21].
Thermodynamic Efficiency of Stokes Shift
The thermodynamic efficiency of the Stokes shift process in 6500K LEDs is not explicitly quantified but can be inferred from various energy losses. Approximately 20% of the incident energy is lost as heat during phosphor conversion, while internal optical losses contribute another 10–30% [1][2]. These losses occur due to re-absorption in the LED chip and packaging.
The efficiency of a white LED is further reduced by the fact that blue LEDs are only about 30–45% efficient. Despite these losses, the final white light output can be 3 to 5 times higher than that of the original blue LED due to human eye sensitivity [1]. However, this measure pertains to photopic efficiency rather than thermodynamic efficiency.
Spectral Mixing and Phosphor Tuning
The resulting white light is a result of spectral mixing between unabsorbed blue light and phosphor-emitted yellow-to-red light. This process is analogous to fluorescent lamps but uses visible blue light as the pump source instead of UV [12].
To achieve a balanced spectrum, manufacturers use phosphor blends that include red-emitting components like manganese(IV)-doped potassium fluorosilicate (PFS) [20]. These blends help mitigate spectral deficiencies in standard YAG-based LEDs and ensure better color rendering.
| Phosphor Type | Emission Wavelength Range | Efficiency |
|–––––|–––––––––|––––|
| YAG:Ce | Yellow-to-red | 90%+ |
| PFS | Red | 85-90% |
Trade-offs in LED Design
The most efficient white LEDs are not those with the most continuous spectra. While a continuous spectrum is desirable for high color rendering, the blue pump with YAG:Ce phosphor produces a more efficient output due to photopic response [1][7].
Advanced designs use remote phosphors or hybrid systems to improve color quality, even though they may be less efficient than single-phosphor LEDs [9][20]. The CCT of 6500K is determined by the precise phosphor composition, balancing blue and red emissions for a cool white appearance.
Key Takeaways
- A 6500K LED converts blue light to white through spectral mixing with YAG:Ce phosphors.
- Thermodynamic efficiency is not quantified but involves significant energy losses due to Stokes shift and optical re-absorption.
- Spectral tuning uses phosphor blends, including red-emitting components for better color rendering.
References
- [1] Light-emitting_diode_-_Wikipedia__ba8713f3 — wikipedia
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Stokes shift and other phosphor-related issues. Their luminous efficacies compared to normal LEDs depend on the spectral distribution of the resultant light output and the original wavelength of the LED itself. For example, the luminous efficacy of a typical YAG yellow phosphor based white LED ranges from 3 to 5 times the luminous efficacy of the original blue LED because of the human eye's greater sensitivity to yellow than to blue (as modeled in the luminosity function). Due to the simplicity of manufacturing, the phosphor method is still the most popular method for making high-intensity white LEDs. The design and production of a light source or light fixture using a monochrome emitter with phosphor conversion is simpler and cheaper than a complex RGB system, and the majority of high-intensity white LEDs presently on the market are manufactured using phosphor light conversion.[39] Among the challenges being faced to improve the efficiency of LED-based white light sources is the development of more efficient phosphors. As of 2010, the most efficient yellow phosphor is still the YAG phosphor, with less than 10% Stokes shift loss. Losses attributable to internal optical losses due to re-absorption in the LED chip and in the LED packaging itself typically account for another 10% to 30% loss. Currently, in the area of phosphor LED development, much effort is being spent on optimizing these devices to higher light output and higher operation temperatures. For instance, the effici
- [2] US7618157B1_-_Tubular_blue_LED_lamp_with_remote_-_Google_Patents__c4fff340 — patent
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LEDs can be selected so that the emitted light has a particular color, such as blue, green, amber, or red. White LEDs often include a blue LED coated with a YAG:Ce phosphor. High power (one watt or more) blue LEDs are about 30-45% efficient, with about 550-700 mW going into heating the device for each watt applied. In addition, the phosphor conversion of blue light into yellow light in a white LED accounts for about 20% of the incident energy, which goes into heating the phosphor. LED technical specifications indicate that blue LEDs have a blue light power depreciation of about 7% (temperature 25-125° C.) while white LEDs have a power depreciation of about 20% at the same temperature. Thus, high power white LEDs impose significant thermal and lumen maintenance constraints. Tubular lamps that use white LEDs are known. However, the LEDs appear as point sources along the length of the tubular cover so the light is not uniform. Some lamps use a refractive cover to the diffuse the light to achieve a more uniform illumination. It is also known to series-connect plural blue LEDs on a PCB board. Various solutions are proposed in U.S. Pat. Nos. 5,463,280; 5,688,042; 5,949,347; 6,036,336; 6,283,612; 6,583,550; 6,634,779; 7,114,830; 7,249,865; 6,762,562; 6,796,680; and 6,940,101. An object of the present invention is to provide a novel lamp that avoids the problems of the prior art. A further object of the present invention is to provide a novel lamp that uses LEDs in a tubular arrangem
- [3] US20110204805A1_-_Color_temperature_tunable_white_light__ec82e505 — patent
source passage
phosphor materials, that is a photo luminescent material, which absorbs a portion of the radiation emitted by the LED and re-emits radiation of a different color (wavelength). Typically, the LED die or chip generates blue light in the visible part of the spectrum and the phosphor re-emits yellow or a combination of green and red light, green and yellow or yellow and red light. The portion of the visible blue light generated by the LED which is not absorbed by the phosphor mixes with the yellow light emitted to provide light which appears to the eye as being white in color. The CCT of a white LED is determined by the phosphor composition incorporated in the LED. – It is predicted that white LEDs could potentially replace incandescent, fluorescent and neon light sources due to their long operating lifetimes, potentially many 100,000 of hours, and their high efficiency in terms of low power consumption. Recently high brightness white LEDs have been used to replace conventional white fluorescent, mercury vapor lamps and neon lights. Like other lighting sources the CCT of a white LED is fixed and is determined by the phosphor composition used to fabricate the LED. – U.S. Pat. No. 7,014,336 disclose systems and methods of generating high-quality white light, that is white light having a substantially continuous spectrum within the photopic response (spectral transfer function) of the human eye. Since the eye's photopic response gives a measure of the limits of what the eye can see
- [7] LED_lamp_-_WikipediaLight-emitting_diode_-_WikipediaLED_circuit_-_Wiki__b8e2933f — wikipedia
source passage
LEDs in conjunction with a phosphor to produce complementary colors from a single LED. Some of the light from the LED is absorbed by the molecules of the phosphor, causing them to fluoresce, emitting light of another color via the Stokes shift. The most common method is to combine a blue LED emitter with a yellow phosphor, producing a narrow range of blue wavelengths and a broad band of "yellow" wavelengths actually covering the spectrum from green to red. The CRI value can range from less than 70 to over 90, although a wide range of commercial LEDs of this type have a color rendering index around 82.[51] Following successive increases in efficacy, which had reached 210 lm/W on a production basis as of 2021, this type has surpassed the performance of trichromatic LEDs. The phosphors used in white light LEDs can give correlated color temperatures in the range of 2,200 K (dimmed incandescent) up to 7,000 K or more.[52] Tunable lighting systems employ banks of colored LEDs that can be individually controlled, either using separate banks of each color, or multi-chip LEDs with the colors combined and controlled at the chip level.[53] LED chips require controlled direct current (DC) electrical power and an appropriate circuit as an LED driver is required to convert the alternating current from the power supply to the regulated voltage direct current used by the LEDs. LED drivers are essential components of LED lamps to ensure acceptable lifetime and performance of the lamp. A drive
- [9] Light-emitting_diode_-_Wikipedia__ba8713f3 — wikipedia
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a mixture of high-efficiency europium-based phosphors that emit red and blue, plus copper and aluminium-doped zinc sulfide (ZnS:Cu, Al) that emits green. This is a method analogous to the way fluorescent lamps work. This method is less efficient than blue LEDs with YAG:Ce phosphor, as the Stokes shift is larger, but it yields light with better spectral characteristics, which render color better. Due to the higher radiative output of the ultraviolet LEDs than of the blue ones, both methods offer comparable brightness. A concern is that UV light may leak from a malfunctioning light source and cause harm to human eyes or skin.[41] A new style of wafers composed of gallium-nitride-on-silicon (GaN-on-Si) is being used to produce white LEDs using 200-mm silicon wafers. This avoids the typical costly sapphire substrate for relatively small 100- or 150-mm wafer sizes.[42] The sapphire apparatus must be coupled with a mirror-like collector to reflect light that would otherwise be wasted. It was predicted that in 2020, 40% of all GaN LEDs are made with GaN-on-Si.[43][needs update] There are RGBW LEDs that combine RGB units with a phosphor white LED on the market. Doing so retains the extremely tunable color of RGB LEDs, but allows color rendering and efficiency to be optimized when a color close to white is selected.[44] Some phosphor white LED units are "tunable white", blending two extremes of color temperatures (commonly 2700K and 6500K) to produce intermediate values. This feature
- [12] LED_Lighting_in_Museums_and_Art_Galleries_Technical_-_Canadaca__7f9b6307 — authority
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the quality of LED lighting. The first LEDs were red, only capable of very low light levels and used as indicator lamps. The development of practical white lighting based on LEDs required more colours (green, then blue) as well as much higher light outputs—problems that were not solved until the 1990s. Different ways to make white LEDs Strictly speaking, there is no such thing as a “white” LED, but the term is used informally to mean a device that produces white light using LEDs. There are three methods of making white light from coloured LEDs: – Phosphor-based: A single LED, either blue or violet, shines its light on a layer of phosphors which fluoresce in the green to red region. The LED is called the “pump” because it pumps energy into the phosphors. The principle is identical to that of fluorescent lamps, which use ultraviolet (UV) radiation from excited mercury vapour to pump the phosphors. The phosphor layer in an LED lamp is designed to allow some of the blue or violet light to escape, so that the final mix of light from the LED pump and the phosphors is white (that is, all the colours of the rainbow). Some manufacturers mix warm and cool white LEDs together to produce a neutral white colour. In Figure 1, the small yellow patches in each lamp are the phosphor layers on top of blue LEDs. – Additive LEDs: These use no phosphors, but only a mix of red, green and blue (RGB) LEDs, which match more or less the three colour receptors of our eyes. This is the same RGB principl
- [13] US8773337B2_-_Color_temperature_tunable_white_light_source__cc1d6185 — patent
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photo luminescent material, which absorbs a portion of the radiation emitted by the LED and re-emits radiation of a different color (wavelength). Typically, the LED die or chip generates blue light in the visible part of the spectrum and the phosphor re-emits yellow or a combination of green and red light, green and yellow or yellow and red light. The portion of the visible blue light generated by the LED which is not absorbed by the phosphor mixes with the yellow light emitted to provide light which appears to the eye as being white in color. The CCT of a white LED is determined by the phosphor composition incorporated in the LED. It is predicted that white LEDs could potentially replace incandescent, fluorescent and neon light sources due to their long operating lifetimes, potentially many 100,000 of hours, and their high efficiency in terms of low power consumption. Recently high brightness white LEDs have been used to replace conventional white fluorescent, mercury vapor lamps and neon lights. Like other lighting sources the CCT of a white LED is fixed and is determined by the phosphor composition used to fabricate the LED. U.S. Pat. No. 7,014,336 disclose systems and methods of generating high-quality white light, that is white light having a substantially continuous spectrum within the photopic response (spectral transfer function) of the human eye. Since the eye's photopic response gives a measure of the limits of what the eye can see this sets the boundaries on high-q
- [17] Technologies_for_Engineering_an_LED_Light_Closest_to_Sunlight__068b3e15 — authority
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# Technologies for Engineering an LED Light Closest to Sunlight Source: Blog/Web URL: https://www.led-professional.com/resources-1/articles/technologies-for-engineering-an-led-light-closest-to-sunlight Author: Date: 2016-09-05 White LED lighting sources were introduced into our social life over ten years ago and have become essential light devices. In comparison to classical lighting devices such as incandescent bulbs and fluorescent lamps, white LED lighting sources have all-round appealing powers; namely they have high energy efficiency, excellent life characteristic and low environmental burden to reduce running costs. And what is more, they can have unrestricted sizes, shapes and output powers to increase the freedom in design of the lighting devices. This is the reason why white LED lighting sources became popular in both facility and home lighting systems. At present, in commercially available white LED lighting devices, blue lights emitted from LED chips are used as exciting light sources to make white light. In concrete terms, a part of blue light from an LED chip is used to be converted into yellow and red lights via appropriate phosphors. Then yellow and red lights are mixed up together with the remaining blue light to turn the mixture into a white light. On this occasion, because the blue light from an LED chip is higher in intensity than the yellow or red lights converted by phosphors, the white light produced by this method, in principle, tends to have a prominen
- [18] US20080252197A1_-_Color_temperature_tunable_white_light__014d4a4c — patent
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each generate white light of differing color temperatures. – the phosphor emits green or yellow light and the second LED arrangement emits red light. – the first LED used to excite the phosphor is operable to emit light in a wavelength range 440 to 470 nm, that is blue light. – light emitted by the first LED arrangement comprises warm white (WW) light with a color temperature in a range 2500K to 4000K and light emitted by the second LED arrangement comprises cold white (CW) light with a color temperature in a range 6000K to 10,000K. – WW warm white – CW cold white – the WW light has chromaticity coordinates CIE (x, y) of (0.44, 0.44) and the CW light has chromaticity coordinates CIE (x, y) of (0.3, 0.3). – the first phosphor emits green light with chromaticity coordinates CIE (x, y) of (0.22, 0.275) and the second phosphor emits orange light with chromaticity coordinates CIE (x, y) of (0.54, 0.46). – the LED used to excite the phosphors is operable to emit light in a wavelength range 440 to 470 nm. – the phosphors share a common excitation source such that the second LED arrangement comprises a respective phosphor provided remote to the first LED and wherein the first LED is operable to generate excitation energy for the two phosphors and the source further comprises a respective light controller associated with each phosphor and the control means is operable to select the color temperature by controlling the light controller to control relative irradiation of the phosphors.
- [20] Light-emitting_diode_-_Wikipedia__ba8713f3 — wikipedia
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like manganese(IV)-doped potassium fluorosilicate (PFS) or other engineered phosphors. PFS assists in red light generation, and is used in conjunction with a conventional Ce:YAG phosphor. In LEDs with PFS phosphor, some blue light passes through the phosphors, the Ce:YAG phosphor converts blue light to green and red (yellow) light, and the PFS phosphor converts blue light to red light. The color emission spectrum or color temperature of white phosphor-converted and other phosphor-converted LEDs can be controlled by changing the concentration of several phosphors that form a phosphor blend used in an LED package.[25][26][27][28] The 'whiteness' of the light produced is engineered to suit the human eye. Because of metamerism, it is possible to have quite different spectra that appear white. The appearance of objects illuminated by that light may vary as the spectrum varies. This is the issue of color rendition, quite separate from color temperature. An orange or cyan object could appear with the wrong color and much darker as the LED or phosphor does not emit the wavelength it reflects. The best color rendition LEDs use a mix of phosphors, resulting in less efficiency and better color rendering.[citation needed] The first white light-emitting diodes (LEDs) were offered for sale in the autumn of 1996.[29] Nichia made some of the first white LEDs which were based on blue LEDs with Ce:YAG phosphor.[30] Ce:YAG is often grown using the Czochralski method.[31] Mixing red, green, and
- [21] US8773337B2_-_Color_temperature_tunable_white_light_source__cc1d6185 — patent
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power supply which is operable to generate a PWM drive current whose duty cycle is used to select a desired color temperature. – PWM pulse width modulated – the light emitting diodes are driven on opposite phases of the PWM drive current. – the first and second LED arrangements emit different colors of light which when combined these appear white in color. – An advantage of such an arrangement to generate white light is an improved performance, in particular lower absorption, as compared to an arrangement in which the LED arrangements each generate white light of differing color temperatures. – the phosphor emits green or yellow light and the second LED arrangement emits red light. – the first LED used to excite the phosphor is operable to emit light in a wavelength range 440 to 470 nm, that is blue light. – light emitted by the first LED arrangement comprises warm white (WW) light with a color temperature in a range 2500K to 4000K and light emitted by the second LED arrangement comprises cold white (CW) light with a color temperature in a range 6000K to 10,000K. – WW warm white – CW cold white – the WW light has chromaticity coordinates CIE (x, y) of (0.44, 0.44) and the CW light has chromaticity coordinates CIE (x, y) of (0.3, 0.3). – the first phosphor emits green light with chromaticity coordinates CIE (x, y) of (0.22, 0.275) and the second phosphor emits orange light with chromaticity coordinates CIE (x, y) of (0.54, 0.46). – the LED used to excite the phosphors is opera
Stokes shift and other phosphor-related issues. Their luminous efficacies compared to normal LEDs depend on the spectral distribution of the resultant light output and the original wavelength of the LED itself. For example, the luminous efficacy of a typical YAG yellow phosphor based white LED ranges from 3 to 5 times the luminous efficacy of the original blue LED because of the human eye's greater sensitivity to yellow than to blue (as modeled in the luminosity function). Due to the simplicity of manufacturing, the phosphor method is still the most popular method for making high-intensity white LEDs. The design and production of a light source or light fixture using a monochrome emitter with phosphor conversion is simpler and cheaper than a complex RGB system, and the majority of high-intensity white LEDs presently on the market are manufactured using phosphor light conversion.[39] Among the challenges being faced to improve the efficiency of LED-based white light sources is the development of more efficient phosphors. As of 2010, the most efficient yellow phosphor is still the YAG phosphor, with less than 10% Stokes shift loss. Losses attributable to internal optical losses due to re-absorption in the LED chip and in the LED packaging itself typically account for another 10% to 30% loss. Currently, in the area of phosphor LED development, much effort is being spent on optimizing these devices to higher light output and higher operation temperatures. For instance, the effici
LEDs can be selected so that the emitted light has a particular color, such as blue, green, amber, or red. White LEDs often include a blue LED coated with a YAG:Ce phosphor. High power (one watt or more) blue LEDs are about 30-45% efficient, with about 550-700 mW going into heating the device for each watt applied. In addition, the phosphor conversion of blue light into yellow light in a white LED accounts for about 20% of the incident energy, which goes into heating the phosphor. LED technical specifications indicate that blue LEDs have a blue light power depreciation of about 7% (temperature 25-125° C.) while white LEDs have a power depreciation of about 20% at the same temperature. Thus, high power white LEDs impose significant thermal and lumen maintenance constraints. Tubular lamps that use white LEDs are known. However, the LEDs appear as point sources along the length of the tubular cover so the light is not uniform. Some lamps use a refractive cover to the diffuse the light to achieve a more uniform illumination. It is also known to series-connect plural blue LEDs on a PCB board. Various solutions are proposed in U.S. Pat. Nos. 5,463,280; 5,688,042; 5,949,347; 6,036,336; 6,283,612; 6,583,550; 6,634,779; 7,114,830; 7,249,865; 6,762,562; 6,796,680; and 6,940,101. An object of the present invention is to provide a novel lamp that avoids the problems of the prior art. A further object of the present invention is to provide a novel lamp that uses LEDs in a tubular arrangem
phosphor materials, that is a photo luminescent material, which absorbs a portion of the radiation emitted by the LED and re-emits radiation of a different color (wavelength). Typically, the LED die or chip generates blue light in the visible part of the spectrum and the phosphor re-emits yellow or a combination of green and red light, green and yellow or yellow and red light. The portion of the visible blue light generated by the LED which is not absorbed by the phosphor mixes with the yellow light emitted to provide light which appears to the eye as being white in color. The CCT of a white LED is determined by the phosphor composition incorporated in the LED. – It is predicted that white LEDs could potentially replace incandescent, fluorescent and neon light sources due to their long operating lifetimes, potentially many 100,000 of hours, and their high efficiency in terms of low power consumption. Recently high brightness white LEDs have been used to replace conventional white fluorescent, mercury vapor lamps and neon lights. Like other lighting sources the CCT of a white LED is fixed and is determined by the phosphor composition used to fabricate the LED. – U.S. Pat. No. 7,014,336 disclose systems and methods of generating high-quality white light, that is white light having a substantially continuous spectrum within the photopic response (spectral transfer function) of the human eye. Since the eye's photopic response gives a measure of the limits of what the eye can see
LEDs in conjunction with a phosphor to produce complementary colors from a single LED. Some of the light from the LED is absorbed by the molecules of the phosphor, causing them to fluoresce, emitting light of another color via the Stokes shift. The most common method is to combine a blue LED emitter with a yellow phosphor, producing a narrow range of blue wavelengths and a broad band of "yellow" wavelengths actually covering the spectrum from green to red. The CRI value can range from less than 70 to over 90, although a wide range of commercial LEDs of this type have a color rendering index around 82.[51] Following successive increases in efficacy, which had reached 210 lm/W on a production basis as of 2021, this type has surpassed the performance of trichromatic LEDs. The phosphors used in white light LEDs can give correlated color temperatures in the range of 2,200 K (dimmed incandescent) up to 7,000 K or more.[52] Tunable lighting systems employ banks of colored LEDs that can be individually controlled, either using separate banks of each color, or multi-chip LEDs with the colors combined and controlled at the chip level.[53] LED chips require controlled direct current (DC) electrical power and an appropriate circuit as an LED driver is required to convert the alternating current from the power supply to the regulated voltage direct current used by the LEDs. LED drivers are essential components of LED lamps to ensure acceptable lifetime and performance of the lamp. A drive
a mixture of high-efficiency europium-based phosphors that emit red and blue, plus copper and aluminium-doped zinc sulfide (ZnS:Cu, Al) that emits green. This is a method analogous to the way fluorescent lamps work. This method is less efficient than blue LEDs with YAG:Ce phosphor, as the Stokes shift is larger, but it yields light with better spectral characteristics, which render color better. Due to the higher radiative output of the ultraviolet LEDs than of the blue ones, both methods offer comparable brightness. A concern is that UV light may leak from a malfunctioning light source and cause harm to human eyes or skin.[41] A new style of wafers composed of gallium-nitride-on-silicon (GaN-on-Si) is being used to produce white LEDs using 200-mm silicon wafers. This avoids the typical costly sapphire substrate for relatively small 100- or 150-mm wafer sizes.[42] The sapphire apparatus must be coupled with a mirror-like collector to reflect light that would otherwise be wasted. It was predicted that in 2020, 40% of all GaN LEDs are made with GaN-on-Si.[43][needs update] There are RGBW LEDs that combine RGB units with a phosphor white LED on the market. Doing so retains the extremely tunable color of RGB LEDs, but allows color rendering and efficiency to be optimized when a color close to white is selected.[44] Some phosphor white LED units are "tunable white", blending two extremes of color temperatures (commonly 2700K and 6500K) to produce intermediate values. This feature
the quality of LED lighting. The first LEDs were red, only capable of very low light levels and used as indicator lamps. The development of practical white lighting based on LEDs required more colours (green, then blue) as well as much higher light outputs—problems that were not solved until the 1990s. Different ways to make white LEDs Strictly speaking, there is no such thing as a “white” LED, but the term is used informally to mean a device that produces white light using LEDs. There are three methods of making white light from coloured LEDs: – Phosphor-based: A single LED, either blue or violet, shines its light on a layer of phosphors which fluoresce in the green to red region. The LED is called the “pump” because it pumps energy into the phosphors. The principle is identical to that of fluorescent lamps, which use ultraviolet (UV) radiation from excited mercury vapour to pump the phosphors. The phosphor layer in an LED lamp is designed to allow some of the blue or violet light to escape, so that the final mix of light from the LED pump and the phosphors is white (that is, all the colours of the rainbow). Some manufacturers mix warm and cool white LEDs together to produce a neutral white colour. In Figure 1, the small yellow patches in each lamp are the phosphor layers on top of blue LEDs. – Additive LEDs: These use no phosphors, but only a mix of red, green and blue (RGB) LEDs, which match more or less the three colour receptors of our eyes. This is the same RGB principl
photo luminescent material, which absorbs a portion of the radiation emitted by the LED and re-emits radiation of a different color (wavelength). Typically, the LED die or chip generates blue light in the visible part of the spectrum and the phosphor re-emits yellow or a combination of green and red light, green and yellow or yellow and red light. The portion of the visible blue light generated by the LED which is not absorbed by the phosphor mixes with the yellow light emitted to provide light which appears to the eye as being white in color. The CCT of a white LED is determined by the phosphor composition incorporated in the LED. It is predicted that white LEDs could potentially replace incandescent, fluorescent and neon light sources due to their long operating lifetimes, potentially many 100,000 of hours, and their high efficiency in terms of low power consumption. Recently high brightness white LEDs have been used to replace conventional white fluorescent, mercury vapor lamps and neon lights. Like other lighting sources the CCT of a white LED is fixed and is determined by the phosphor composition used to fabricate the LED. U.S. Pat. No. 7,014,336 disclose systems and methods of generating high-quality white light, that is white light having a substantially continuous spectrum within the photopic response (spectral transfer function) of the human eye. Since the eye's photopic response gives a measure of the limits of what the eye can see this sets the boundaries on high-q
# Technologies for Engineering an LED Light Closest to Sunlight Source: Blog/Web URL: https://www.led-professional.com/resources-1/articles/technologies-for-engineering-an-led-light-closest-to-sunlight Author: Date: 2016-09-05 White LED lighting sources were introduced into our social life over ten years ago and have become essential light devices. In comparison to classical lighting devices such as incandescent bulbs and fluorescent lamps, white LED lighting sources have all-round appealing powers; namely they have high energy efficiency, excellent life characteristic and low environmental burden to reduce running costs. And what is more, they can have unrestricted sizes, shapes and output powers to increase the freedom in design of the lighting devices. This is the reason why white LED lighting sources became popular in both facility and home lighting systems. At present, in commercially available white LED lighting devices, blue lights emitted from LED chips are used as exciting light sources to make white light. In concrete terms, a part of blue light from an LED chip is used to be converted into yellow and red lights via appropriate phosphors. Then yellow and red lights are mixed up together with the remaining blue light to turn the mixture into a white light. On this occasion, because the blue light from an LED chip is higher in intensity than the yellow or red lights converted by phosphors, the white light produced by this method, in principle, tends to have a prominen
each generate white light of differing color temperatures. – the phosphor emits green or yellow light and the second LED arrangement emits red light. – the first LED used to excite the phosphor is operable to emit light in a wavelength range 440 to 470 nm, that is blue light. – light emitted by the first LED arrangement comprises warm white (WW) light with a color temperature in a range 2500K to 4000K and light emitted by the second LED arrangement comprises cold white (CW) light with a color temperature in a range 6000K to 10,000K. – WW warm white – CW cold white – the WW light has chromaticity coordinates CIE (x, y) of (0.44, 0.44) and the CW light has chromaticity coordinates CIE (x, y) of (0.3, 0.3). – the first phosphor emits green light with chromaticity coordinates CIE (x, y) of (0.22, 0.275) and the second phosphor emits orange light with chromaticity coordinates CIE (x, y) of (0.54, 0.46). – the LED used to excite the phosphors is operable to emit light in a wavelength range 440 to 470 nm. – the phosphors share a common excitation source such that the second LED arrangement comprises a respective phosphor provided remote to the first LED and wherein the first LED is operable to generate excitation energy for the two phosphors and the source further comprises a respective light controller associated with each phosphor and the control means is operable to select the color temperature by controlling the light controller to control relative irradiation of the phosphors.
like manganese(IV)-doped potassium fluorosilicate (PFS) or other engineered phosphors. PFS assists in red light generation, and is used in conjunction with a conventional Ce:YAG phosphor. In LEDs with PFS phosphor, some blue light passes through the phosphors, the Ce:YAG phosphor converts blue light to green and red (yellow) light, and the PFS phosphor converts blue light to red light. The color emission spectrum or color temperature of white phosphor-converted and other phosphor-converted LEDs can be controlled by changing the concentration of several phosphors that form a phosphor blend used in an LED package.[25][26][27][28] The 'whiteness' of the light produced is engineered to suit the human eye. Because of metamerism, it is possible to have quite different spectra that appear white. The appearance of objects illuminated by that light may vary as the spectrum varies. This is the issue of color rendition, quite separate from color temperature. An orange or cyan object could appear with the wrong color and much darker as the LED or phosphor does not emit the wavelength it reflects. The best color rendition LEDs use a mix of phosphors, resulting in less efficiency and better color rendering.[citation needed] The first white light-emitting diodes (LEDs) were offered for sale in the autumn of 1996.[29] Nichia made some of the first white LEDs which were based on blue LEDs with Ce:YAG phosphor.[30] Ce:YAG is often grown using the Czochralski method.[31] Mixing red, green, and
power supply which is operable to generate a PWM drive current whose duty cycle is used to select a desired color temperature. – PWM pulse width modulated – the light emitting diodes are driven on opposite phases of the PWM drive current. – the first and second LED arrangements emit different colors of light which when combined these appear white in color. – An advantage of such an arrangement to generate white light is an improved performance, in particular lower absorption, as compared to an arrangement in which the LED arrangements each generate white light of differing color temperatures. – the phosphor emits green or yellow light and the second LED arrangement emits red light. – the first LED used to excite the phosphor is operable to emit light in a wavelength range 440 to 470 nm, that is blue light. – light emitted by the first LED arrangement comprises warm white (WW) light with a color temperature in a range 2500K to 4000K and light emitted by the second LED arrangement comprises cold white (CW) light with a color temperature in a range 6000K to 10,000K. – WW warm white – CW cold white – the WW light has chromaticity coordinates CIE (x, y) of (0.44, 0.44) and the CW light has chromaticity coordinates CIE (x, y) of (0.3, 0.3). – the first phosphor emits green light with chromaticity coordinates CIE (x, y) of (0.22, 0.275) and the second phosphor emits orange light with chromaticity coordinates CIE (x, y) of (0.54, 0.46). – the LED used to excite the phosphors is opera