Fundamentals: LED color chart article gives a brief review on color temperature and how it affects white LED light.
Despite the fact that LEDs produce light by a process other than heating, we still use correlated color temperature (CCT) when describing the appearance of the LED as it relates to the appearance of a black body radiator. Color Temperature is a standard method of describing white color for use in a range of situations and with different equipment, but note that the term degrees kelvin is not technically correct.
Most white LED lamps fall under three basic categorical descriptions: “warm white,” “pure white,” and “cool white.” When the glow of the white LED light is slightly yellow, it’s typically around 3000° Kelvin (K), referred to as “warm white.” “pure white” LED light measures at around 4500°K. “cool blue” white light displays a reading of 6500°K or more. Standard for White Color LED Lighting Fixtures document outlines a proposed definition of standard for white color LED lighting fixtures defined within C.I.E. 1931 chromaticity diagram (degrees Kelvin only as a reference measurement).
Warm light is best used in living spaces as it tends to be more flattering to clothing and skin tones. Cool light, on the other hand, is preferred for visual tasks, as it produces excellent contrast. Fundamentals: LED color chart has a table on the end of the article that shows easy-to-remember basics for best application practices for different applications. Which Color Temperature Do You Prefer?
For more LED information read also Notes on LEDs article.
20 Comments
Dong says:
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Tomi Engdahl says:
LED light: Overall lousy color rendering – What can be done to fix this?
http://www2.electronicproducts.com/TechXchange_Forum.aspx?mode=thread&id=3061#3795
One thing I have noticed about “white” LEDs is although they simulate white light across the color temperature range, they are actually “peaky” from a spectrum point of view, most with a strong blue peak and another strong yellow to yellow-orange peak. That is going to have a drastic effect on color rendition.
How to improve the color “filling” of LED based lamps for reading with smooth and uniform color mixing at competitive cost?
Some recent lamps have very high color rendering capability. See for example
Bright LED modules give high color rendition
http://www2.electronicproducts.com/Bright_LED_modules_give_high_color_rendition-article-oprc05_nov2011-html.aspx
Intended for lighting applications in which rendition of color is paramount, the XSM Artist 1000 series LED module delivers up to 1,000 lm with an average CRI (Ra) greater than or equal to 95.
Intematix Phosphor Blend Accomplishes Near Perfect Light Quality for LEDs
http://www2.electronicproducts.com/Intematix_Phosphor_Blend_Accomplishes_Near_Perfect_Light_Quality_for_LEDs-article-newsrc01_13_oct2011-html.aspx
98 CRI milestone for light quality drives LED adoption in retail, hospitality, residential and museum applications
Intematix Corporation, a leading innovator of patented phosphor materials and components for high-quality LED lighting, today announced that it has demonstrated a phosphor blend that provides a near perfect color rendering index (CRI) of 98 and R9 value of 99 when applied to a reference LED package.
“Reaching 98 CRI is huge it means that by adding Intematix phosphor, an LED package can render true color,”
Tomi Engdahl says:
Understand the science behind color mixing
http://www.eetimes.com/design/analog-design/4236909/Understand-the-science-behind-color-mixing?Ecosystem=analog-design&cid=NL_UBM+Electronics
High-brightness (HB) LEDs continue to increase in popularity due to the numerous advantages they offer when compared to the conventional lighting solutions. One of the advantages of HB LEDs is their ability to generate different colors, opening a new dimension to the world of decorative lighting.
Color mixing is essentially a process where a secondary color is generated by mixing the appropriate proportion of base primary colors. This article will explain the science behind color mixing, including the mathematical equations involved and how to implement them efficiently.
Tomi Engdahl says:
Exposure to ‘White’ Light LEDs Appears to Suppress Body’s Production of Melatonin More Than Certain Other Lights, Research Suggests
http://www.sciencedaily.com/releases/2011/09/110912092554.htm
Exposure to the light of white LED bulbs, it turns out, suppresses melatonin 5 times more than exposure to the light of high pressure sodium bulbs that give off an orange-yellow light. “Just as there are regulations and standards for ‘classic’ pollutants, there should also be regulations and rules for the pollution stemming from artificial light at night,” says Prof. Abraham Haim of the University of Haifa.
The fact that “white” artificial light (which is actually blue light on the spectrum, emitted at wavelengths of between 440-500 nanometers) suppresses the production of melatonin in the brain’s pineal gland is already known. Also known is the fact that suppressing the production of melatonin, which is responsible, among other things, for the regulation of our biological clock, causes behavior disruptions and health problems.
Thanh Hossler says:
Hey, Nicely written blog. Never seen indoor plants take growth like this. These might just be the lowest cost to own light units for cultivating dank out there.
Tomi Engdahl says:
Accurately Plot Colors from Power Spectrum Data
http://www.edn.com/design/led/4375668/Accurately-Plot-Colors-from-Power-Spectrum-Data?cid=EDNToday
Accurate color mixing of light from LEDs requires precise knowledge of the primary colors used for mixing. While some manufacturers provide bin data for color LEDs, many do not. What is almost always provided is a power spectrum diagram of the LED.
CIE1931 standard observer functions (Figure 1a, b and c) are available directly from CIE. Recreate the LED spectrum power in Microsoft Excel by tracing a screen capture from the LED datasheet.
Calculating coordinates for red, green, and blue light sources is the first step towards accurately mixing RGB primaries to obtain a desired color. When the desired output is white light, an understanding of the Planckian black body model is also required.
Tomi Engdahl says:
Add LED Intelligence–Improve light quality, efficiency and cost
http://www.edn.com/design/led/4392263/Add-LED-Intelligence-Improve-light-quality–efficiency-and-cost?cid=EDNToday
As the lighting industry continues to make the transition to LED technology, there is an increasing need for more intelligent controllers and drivers. The rising price of electricity presents a major operating cost to consumers and businesses; however, efficient operation of LEDs can result in substantial savings. Many applications need to produce consistent light quality while supporting advanced control functionality such as dimming, balancing, and accurate color mixing. Remote connectivity is also becoming a regular requirement in applications where high-maintenance expenses can be reduced through self-diagnostics that allow technicians to make a service call only when there is an actual reason to visit a site.
Bringing intelligence into many LED lighting applications may require moving from fixed function LED drivers to microcontroller-based, or programmable architectures.
Tomi Engdahl says:
Space Farmers: LEDs As Key To NASA’s Permanent Lunar Life Support
http://www.forbes.com/sites/brucedorminey/2012/08/31/space-farmers-leds-as-key-to-nasas-permanent-lunar-life-support/
future off-worlders will need bio-regenerative systems in order to prosper.
Here on earth, researchers still debate how best to make those possible, but nuclear-powered state of the art LED (Light-emitting Diode) technology is arguably what will drive photosynthesis so necessary to provide both food and oxygen for future lunar colonists.
the most practical solution is simply to use some sort of Radioisotope Thermoelectric Generator (RTG), not unlike the one powering the current Mars Science lab, to power the LEDs that will spur photosynthesis in lunar greenhouses.
Cary Mitchell, a plant biologist at Purdue University, says that as lunar light sources, LEDs would be cool, solid state and robust; lasting 50,000 hours at least, or some five times longer than conventional horticultural light sources.
LEDs also allow growers to tailor their light spectrum to manipulate and maximize certain plant attributes, thereby increasing a plant’s given nutraceutical content.
Tomi says:
Bin Coding: Color, Flux and Vf Charts and Links for Popular White LEDs
http://www.candlepowerforums.com/vb/showthread.php?156772-Bin-Coding-Color-Flux-and-Vf-Charts-and-Links-for-Popular-White-LEDs
gymnastikmatte says:
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Tomi Engdahl says:
What testing is needed for an LED?
http://www.edn.com/design/test-and-measurement/4401983/What-testing-is-needed-for-an-LED?cid=EDNToday
The recent ban on the incandescent light bulb, government incentives, and the ingenuity of industry experts have all played a role in LEDs becoming the predominant new product in the North American lighting market today. As this technology continues to rapidly evolve, lighting manufacturers and others involved in the industry are finding it increasingly challenging to validate product claims and keep up with industry standards and testing requirements.
In an attempt to offset the price, lighting manufacturers highlight the performance of their products, some claiming 10-year lifespans compared to the typical one-to-two-year lifespan of traditional lighting products. Since these marketing claims are difficult to prove, new criteria has recently been developed for LEDs to help manufacturers avoid customer backlash and negative publicity and provide verification for their products.
Tomi Engdahl says:
Correction Technique Adds ‘Warmth’ to Dimmable LED Light
http://www.designnews.com/author.asp?section_id=1395&doc_id=257274&cid=NL_Newsletters+-+DN+Daily
Engineers at NXP Semiconductors say they’ve found a way to take the “coldness” out of dimmable white light-emitting diode (LED) light.
Using a combination of new technologies that earned the company 15 patents, the company’s engineers can reportedly remove the harshness from white LEDs and replace it with the “warmer” combination of yellow and white that’s familiar to consumers
“LED lights have always had this cold white — a hospital white,” Radu Sudeanu, senior scientist for NXP, told Design News. “But now we know how to correct it to get the right color.”
With its new technology, NXP hopes to make LEDs acceptable to a broader swath of consumers. In the past, some retailers have reportedly received dimmable white LEDs back from unhappy customers, some of whom say the light is too much like that of a fluorescent bulb. “Many people don’t like it,” Surdeanu told us. “They want the same yellowish light that we’ve all grown accustomed to for a hundred years with the Edison bulb, and for a thousand years before that with fire.”
NXP engineers remove “coldness” from LED light with a three-pronged solution. By combining the black body radiation curve (which relates light wavelength to light intensity) of an incandescent bulb with a logarithmically-based dimming technique, and then correcting for temperature variation, they say they can produce a color that lies between amber and white.
Tomi says:
Horticulture LED Technology
LEDs Create a Virtual Spring!
http://www.electronicproducts.com/Optoelectronics/Horticulture_LED_Technology.aspx
For those of us here in the U.S. and across the northern hemisphere, spring is on the way—growing season for farmers, gardeners, and enthusiasts. But with new technology they no longer have to rely on the sun to grow their favorite plants. The latest horticulture LEDs are providing new options to grow year round, even in places which couldn’t support regular farming—such as urban factories and multistory warehouses.
Research has shown that particular wavelengths of light play different roles in how plants grow. Plants respond better to wavelengths specifically in the 400 to 500nm (blue) and 600 to 700nm (red) spectra.
Growth is strongly influenced by the number of photons absorbed in the photosynthetically active radiation (PAR) region, which covers only 45 percent of the total light spectrum.
Scientists are currently studying how to cook up lighting “recipes” for specific horticultural uses.
In horticultural applications, using Lux or lumens as a measure of light output is deemed inappropriate, as they imply a heavily biased human perception of light. Photosynthetic photon flux density (PPFD) is a more appropriate measure for the light energy that reaches the surface of plants
Tomi Engdahl says:
LED for Covert Surveillance
http://showcase.designnews.com/content/led-covert-surveillance?cid=NL_Newsletters+-+DN+Daily
The infrared Oslon black SFH 4725S LED from Osram Opto Semiconductors has a wavelength of 940 nanometers, making it nearly invisible to the human eye, and its black package reflects virtually no ambient light. Together with its high optical output power of almost one watt, this infrared LED is the ideal light source for covert surveillance applications.
Concealed security systems – such as those installed in banks, on machinery and at border crossings –need to be designed so they are unobtrusive. This is a major challenge for infrared illumination in such applications because the 850 nanometer (nm) LEDs that are typically used here appear as weak dots of red light, especially in dark environments, giving away the cover of security cameras. The solution is to switch to a wavelength of 940 nm, which the human eye is 130 times less likely to notice. Camera sensors, however, can easily detect this invisible radiation.
This compact infrared LED provides 940 nm light with a high optical output of 980 milliwatts from an operating current of 1 Amp.
Tomi Engdahl says:
RGBW LED emitters boast 30% more output
http://www.edn.com/electronics-products/other/4412126/RGBW-LED-emitters-boast-30–more-output
The LZ4 flat lens family of compact, 4-die RGBW emitters from LED Engin is designed for wash lamps and follow spots in stage lighting applications. Two varieties are available. The LZ4 can be driven to 1A and LZ4-Plus to 1.5A per die, with 550 and 725 lumens output respectively. This represents 30% more than competitive products, according to the company.
The emitters individually address each die in conjunction with in-source color mixing, without attaching color filters to lamps.
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Lyon Vaise says:
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