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Home » Energy saving

LED colour quality, CRI and binning.

Submitted by on Saturday, 29 August 2009 Loading Add to favourites  14 Comments
What is white light?

What is white light?

One main criticism of LEDs used for room and space lighting is that the colour or hue of the light appears cold and harsh. Some LEDs appear as tiny, brilliant lights that are too bright to look at, but seem to give very little illumination. There is a quantitative measure of the ability of a light source to reproduce the colors of various objects faithfully in comparison with an ideal or natural light source called Colour rendering index, or  CRI. We are used to a much warmer light from conventional incandescent lights because filament bulbs have a broader spectrum of light that is biased towards the warm red frequency.

White light

White light is made up of all colours, which is why we see colours of objects evenly when lit by a balanced white light. If we reduce the output of any colour in a white light source, we reduce the reflective strength of that colour in objects. For example if we look at a ripe tomato under a blue light, we don’t see its red colour, because there is no red light available to reflect off it and onto our eyes. The ability to render colours fully and accurately is one major drawback with LED lighting that has not been desiged correctly.

Colour temperature

Color “Temperature” is a measure of the relative amounts of red or blue light being emitted.  It is not a measure of temperature at all. Most commercially available LEDs aim to provide the highest luminous efficacy, meaning the brightest light output in Lumens for a standard of one watt of electricity used. These high powered LEDs use InGaN, GaN (gallium nitride) in the emitter and tend to produce the highest light output. The problem is there is a dominance of blue in the light, peaking at about 465nm and less of the red light that gives the impression of warmth. In order to correct this, the favoured method is to coat the InGaN emitter with phosphor of different colors, the phosphor absorbs the light energy and emits a more balanced output with a wider spectrum to produce white light.  A fraction of the blue light undergoes the stokes fluorescence being transformed from shorter wavelengths to longer (500–700 nm.). Depending on the colour of the original LED, phosphors of different colours can be used. If several phosphor layers of distinct colors are applied, the emitted spectrum is broadened, effectively increasing the color rendering index (CRI) value of a given LED.  These LEDs are called phosphor based white LEDs.

The warmer the Light, the lower the lumens/watt

Image shows GaN LED and Phosphor coated LED comparing intensity and spectrum output.

Image shows GaN LED and Phosphor coated LED comparing intensity and spectrum output.

Unfortunately, the warmer light output of phosphor based LEDs is considerably lower in lumens than the uncorrected versions and  this is an area of development still requiring more research. This means Warm white LEDs produce lower lumens (light brightness) than daylight or natural white LEDs

See
http://en.wikipedia.org/wiki/Light-emitting_diode for an indepth article on this and better image.

Mixing colours to make the right white

Another method  to improve white light quality is to use LEDs with 3 distinct RGB emitters that can be individually tuned to output the desired mix of light giving a broad spectrum of colours and hues. Using the principle that all visible colours are made up of a balance of Red, Green and Blue primary colours. These LEDs require a control circuit to adjust the different mix of outputs and are less practical as direct replacement of conventional lighting. However, there are some RGB LEDs that come with a remote control pad that allows you to select any colour you want, rotate sequences and produce white of any hue, warm, neutral, daylight, or very intense.

Binning and labelling

Guide tocolout tints in LED lighting

For the DIY LED enthusiast, there is another definitive guide that helps greatly in deciding the colour quality of the LED. Quality manufacturers such as SMD, Cree, Seol, Philips and Nichia provide detailed specification data sheet for their LED emitters. Along with technical details of forward voltage and current requirements, these manufacturers will also show a codes relating to a particular LED range and its colour output based on the CRI or colour rendering index, as discussed earlier. Put simply, this labelling follows a prescribed measurement of what sort of white the output is, taking into account, the dominant wavelength and scope of the total output. This means you can buy a LED emitter and choose a binning code that gives you cold white, daylight white, natural white, warm white, or some other description. What is important for the user is to understand the actual colour temperature in Kelvin according to the table below. When a white LED is described in this way what it means is that it will have a dominant tint or hue to the light ranging from red to the blue end of the spectrum. This gives the subjective feeling of warmth or coolness.

For a more detailed insight to Binning and labeling, please see a typical data sheet from Cree here

Putting it together

LED technology is improving all the time. Efficient production methods, higher light output and better colour quality is emerging making LED lighting more attractive for manufacturers, home users and lighting contractors.  There is a technology lag between what is available from the cutting edge of development and what we can buy in the high streets. Most commercially available LED lights are either Just about bright enough to replace a halogen, but too blue, or hardly better than a flashlight if it has a broader and warmer colour spectrum.
Rule of thumb for white light: The warmer the white, the lower the light output, in terms of lumens per watt
A 500 lumen warm LED light will need to be more powerful, in terms of watts that a cold light version.
There is no doubt that LEDs will lead the green lighting revolution, but right now, there are too few commercially available lights to really impress the skeptics or ordinary consumer. Some manufacturers and retailers are releasing a new breed of LEDs that give both high light output and good colour quality The DIY hobbyist, however, has access to build LED light units that really fulfill all the criteria of brightness, colour quality, energy efficiency and cost.

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14 Comments »

  • F-entremish says:

    That’s very interesting Mr Green. I bought an LED spotlight a while ago and I was very disappointed in the quality of light. Not only was it a very blueish light, but it was not as powerful as I expected. Far too expensive also.. from B&Q in Milton Keynes.

    Done some internet browsing and I have found some other LEds available. How do I know they will be better? Any pointers?
    Thanks Fred.

  • Mr Green says:

    Hello Fred. Ultimately, you have to “see” what the LED is like. We are a long way from a standard that guarantees a consitency of light quality. So many factors, such as the housing the LED emitter is built into … the reflector, diffuser, lens, angle of light dispersion. It goes on. Some retailers do provide a demonstration booth, or have lights on display.I think you need to go and see the light and get a feel for it.

    Some things to look out for

    1- If you want a soft light from a LED, go for a “warm light”
    2- Ask if the LED is for a spot light, room lighting with a wide angle of dispersion
    3- Make sure you get a LED with at least 3 watt power. Anything less is no better than a candle
    4- If you want to light a whol room with an LED, you need a light output of at least 1000 lumens (this is just under the equivelent of an ordinary 100 watt light bulb.

    I’ll have some more specific details coming up soon…

  • SarahG says:

    I really think this is all too complicated. It’s like I have to become conversant in CRI/ Lumens/ Binning and labelling before I can really an informed choice about LEDs. Isn’t there a more straight forward version? I DO see the importance of the green idea here, but I need some basic help

  • Mr Green says:

    @SarahG: You’re absolutely right SarahG. And I have left out lots of other small details to try and keep it simple!

    As I said to Fred in my last comment, we are missing a recognised standard for LED light quality. We take the old light bulb so much for granted, because we are used to what it will look like, how it will perform and all those details that are important.

    LED lighting is so different and comes with a whole new set of characteristics and problems. In many ways to compare an old incandescent light with an LED is like comparing apples and pears.

    Until we have more commonality we really must “see” to experience what an LED is like.

    This prompts me to do something to help: I’m going to make some video of all the LED projects I’ve done in our home and office and show some real life examples of how good LED lighting can be. Also point out it’s problems with light quality. I’ll do this in HD quality, so you can really see what’s happening.

    Thanks for your comment Sarah.

  • Mrs Green says:

    @F-entremish: Hi Fred, welcome to the site. As a consumer, you pose the exact same questions and disappointments I had myself when first ever looking into LED lighting. Let’s hope things change quickly so that the range of products is better and cheaper.

    @SarahG: Sarah – hi; another great point. Many people do not have time to learn all about colour, lumens and all of that. I only know the words because of Mr G’s work, but as a consumer I don’t have much of a clue. We have all become so used to knowing what a 40,60 or 100w incandescent light bulb looks like and we haven’t needed to know anything else.
    You’ll be amazed at the quality of the lighting Mr G has been working on here and I hope similar products hit the high streets soon.

  • Jeff Chan says:

    Great article Mr. Green for both DIY’s as well as people just shopping around for LED bulbs. It’s all about making people more informed. Where with incandescent bulbs, an incandescent is an incandescent and they’ve become a commodity. With LED bulbs the range in both pricing and quality from one bulb to another is huge. We’ve tested a bunch of them.
    @F-entremish: You should look for atleast a 2 Year Warranty on products. Lumens, CRI and “light replacement equivalent” are often mis-stated – unless they’ve been tested by a third party lab I’d take these ratings with a grain of salt. Also look for side-by-side picture comparisons – this is what we’ve found to be a great way to show both the color output and light quality of our products.

  • […] guys over at littlegreenblog.com have written a GREAT article on exactly what CRI and Color Temperature are and how to get the exact LEDs you need if you plan to build your own LED lights. It’s a […]

  • Layla says:

    Great to see a blog post on LEDs too!!

    I’m hugely interested in whether they are recyclable and recyclED – any info on that front yet? :)

    And yes, it’s all greatly confusing for me too!
    I have a ‘decor-LED’ it’s sort of like a candle or less and very relaxing for times when my eyes were very stressed!!

    Some people said quite strong LED reflectors exist already, haven’t tried or seen ‘in action’ any of those yet..

  • Layla says:

    Oh, and Mr Green *built DIY LEDs*?!! /faints/

    Now I adore him even more!! Mrs Green you are soo lucky!! :)

  • Mrs Green says:

    @Layla: Hi Layla, well I won’t argue with you; I am a very lucky woman ;) He is a genius and so creative; it still amazes me, even after all this time.

  • Mr Green says:

    Hi @Layla: Hi Leyla. The recycling question is still not really addressed, but as I said in the otjer comment, we should not need to recycle LEDs for a long time yet. You may be interested to know that the lifecycle of a LED is NOT measured from “start to finish”, but from “start untill the light quality begins to deteriate are grow dim” They do not ‘blow’ or ‘pop’ but ever so slowly produce less light.

    In fact we can get LEDs that cover every sort of light, from brilliant white to every colour available in the spectrum. From my experience in using and building them, I can say that careful design and use of a shade or light diffuser is very important to modify the light to make it soft and pleasant in the home.

  • A good article for consumers trying to get information when replacing incandescent bulbs. Here in British Columbia, Canada as of Jan 1st 2011 incandescent bulbs are no longer legally sold. The article remains timely.

  • Mrs Green says:

    @Michael Rupkalvis: Michael, welcome to the site; we never knew that Canada had banned the incandescent bulb so thank you for updating us :)

  • The ban will be nation wide in Canada next year due to federal legislation. British Columbia acted unilaterally in banning them this year. I am not sure if any other provinces have done the same but I do not think so.