How to improve the color "filling" of LED based lamps for reading with smooth and uniform color mixing at competitive cost?
Pierre, what do you want to use the LED based lamp for? Some recent lamps have very high color rendering capability. See for example www.electronicproducts.com/B-article-oprc05_nov2011-html.aspx
The lamp is planned to be a tabletop reading lamp. Currently we use 4 MX-3S warm white LED, a cost effective solution.
Thank you for the link, yes this remote phosphor variation appears to be a quantum leap forward for color rendering vs what we use currently but it would be a new lamp.
You may want to talk with a company called Intematix (http://www2.electronicproducts.com/Intematix_Phosphor_Blend_Accomplishes_Near_Perfect_Light_Quality_for_LEDs-article-newsrc01_13_oct2011-html.aspx). They can supply phosphors for correcting any LED to match your color preference.
I understand, we picked the wrong LED for the application, should have picked a : 90< CRI for reading lamp.
Thank you very much Richard for sharing this information.
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.
All LEDs are not created equal! There is a selection process called "binning" which segments LEDs into different categories. One can bin on color temperature, forward voltage, luminous flux, proximity to the Plankian locus and CRI. So you can get LEDs which render colors very well. You just have to ask for them and pay the price for binning. There is an ANSI standard for binning on color, but many manufacturers offer tighter bins, We have found that some manufacturers do a better job than others in this department, so check out samples before committing yourself to purchases.
True to a certain extent but I don't think most manuracturers bin on CRI. A few do. The major issue is the width of the secondary curve for the phosphors (ignoring RGB LEDs for the moment). The broader the phosphor curve the better (in general) the color rendition. So warm white LEDs generally have the best color rendition. Cool or cold LEDs tend to be very peaky (especially in the blue region) and therefore have poor color rendition unless you are illuminating a picture of the sky and the sea. As to RGB LEDs, they have three individual & narrow peaks - red, green & blue and thus tend to have poor CRI.
For those who are not familiar with this, the subject is how LEDs illuminate objects that are colored (e.g., a McBeth or Kodak color checker), not how the LED approximates white light itself.
I was using binning in the broad sense of the word :). You can buy high CRI LEDs from various manufacturers. We have found that performance varies widely. I am known as "Mr Colorchart" to a few manufacturers because I carry a chart with me when I attend shows as I have learned to "trust my eyes" rather than believe everyone's specs. We produce a high CRI luminaire for the photographic, jewelry, art, machine vision, printing, scanning and fashion industries. It has a Ra of above 94 with R1-R14 all above 90, So We know what is possible with good selection and design. We have also developed our own software which takes the output of a spectroradiometer/integrating sphere and produces a single page document which gives you a picture of performance. It includes a spectral power diagram, CRI graph from R1-R14/15 and location within the 1931 color space including proximity to the Planckian locus together with a listing of other key parameters. I am happy to discuss this further either in this forum or privately as it is very technical!
It would be great for us and anyone who stumbles across this forum to find a technical discussion on CRI and relevant paramaters. I know I would appreciate it.
Noor, have you seen this article: http://www.digikey.com/us/en/techzone/lighting/resources/articles/color-rendering-of-light-sources.html?