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Discussion Starter · #1 ·
Just a quick question about the relation between CCT and CRI.

I understand what both are on their own, but I don't understand how or if they relate to one another.
Question is this. If i have a light that has a CCT of 11000 this would suggest a blue color if i am not mistaken. Now if that same light has a CRI of 96 would that not suggest that the color reproduction under that light would be very accurate? so if the light is blue...would I notice since the CRI is so high?
 

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Just a quick question about the relation between CCT and CRI.

I understand what both are on their own, but I don't understand how or if they relate to one another.
Question is this. If i have a light that has a CCT of 11000 this would suggest a blue color if i am not mistaken. Now if that same light has a CRI of 96 would that not suggest that the color reproduction under that light would be very accurate? so if the light is blue...would I notice since the CRI is so high?
Neither matters or is very important to plants or fish.. There got that out of the way..

I've come to the "personal" conclusion CRI is rather meaningless (esp in regards to LED's)s.. It is the color "accuracy" of 8 patches (or 10) calibrated under a specific light.. As such a high CRI can appear "wrong".. while a low CRI can appear correct to your eyesight. As to what color right or wrong it is well...???
As specified in CIE (1995), the original test color samples (TCS) are taken from an early edition of the Munsell Atlas. The first eight samples, a subset of the eighteen proposed in Nickerson (1960), are relatively low saturated colors and are evenly distributed over the complete range of hues.[17] These eight samples are employed to calculate the general color rendering index R_a.
See wiki for details...
CT well that is it's "color" so to speak..(CCT is a bit different.. but hey..)
The CRI of a light source does not indicate the apparent color of the light source; that information is under the rubric of the correlated color temperature (CCT)
http://lowel.com/edu/color_temperature_and_rendering_demystified.html

As a side note, from what I read, they are "working on" changing how they determine CRI specifically because LED's are "different"
As to my understanding white LED's usually "score" low on a CRI scale yet are visually perceived as accurate or pleasing on a personal level.. thus the problem..It has to do w/ the fact that they are realy blue LED's w/ yellow phosphors..
http://en.wikipedia.org/wiki/Color_rendering_index
CIE (2007) "reviews the applicability of the CIE color rendering index to white LED light sources based on the results of visual experiments." Chaired by Davis, CIE TC 1-69(C) is currently investigating "new methods for assessing the color rendition properties of white-light sources used for illumination, including solid-state light sources, with the goal of recommending new assessment procedures ... by March, 2010."[27]
A bit of clarity on CCT..
Light sources that are not incandescent radiators have what is referred to as a "Correlated Color Temperature" (CCT). It's connotations to any part of the color temperature chart are strictly visually based. Lights with a correlated color temperature do not have an equal radiation at all wavelengths in their spectrum. As a result, they can have disproportionate levels (both high & low) when rendering certain colors.
Point is if it has a CCT of 6000 it "looks" like a 6000k black body radiation pattern but it may be composed of say. 50% 9000k and 50% 3000K emission bands.
 

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Discussion Starter · #3 ·
So what you are saying is that neither CCT nor CRI mean anything and are not important when it comes to led's?
All i am looking to do really is to put together my BML light and have reached the point that i am ready to order but have received comments such as "well i hope you like blue because the main color in your spectrum is blue". which confused me as my CRI in said spectrum is 96. not sure how with a 96 CRI that things would look blue. I'm just confused.
 

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So what you are saying is that neither CCT nor CRI mean anything and are not important when it comes to led's?
All i am looking to do really is to put together my BML light and have reached the point that i am ready to order but have received comments such as "well i hope you like blue because the main color in your spectrum is blue". which confused me as my CRI in said spectrum is 96. not sure how with a 96 CRI that things would look blue. I'm just confused.
Lets go a bit in the opposite direction I could also design a light w/ high CRI that looked yellow..


Your better judge of color tone is where it lies on the CIE diagram..
As I found out CRI is a bit problematic w/ LED's
I remember getting high scores on the LED calc at BML but not sure if it got that high..(opps guess I did)
EXAMPLE your CCT 10639K.. a bluewhite.. ;) but plenty of other color tones to compensate.. Yes it could apper slightly blue but not bad at all.. Once the plants fill in you won't even notice it.. White objects might seem a bit "cool" looking..


CRI 96 but 2 totally different "tones" CCT 6035K


I guess it is best to think of it this way:
Color rendering index (CRI) is how a bulb performs while the correlation color temperature (CCT) had been created to place the bulbs in the right position on this scale. In other words, CRI measure the quality of light while CCT is different color of the light
http://ledspots.org/color-rendering-index/

Think of the 4% deviation being at certain colors..
Or this:
In the previous post we looked at the color temperature, or color of the light. That actually has little to do with color rendering, which is the color of the objects under the light. See the difference? Either a warm source like incandescent or a cool source like daylight can render the color of objects nearly perfectly
http://www.envisionlightingdesign.c...s-the-difference-between-a-cct-and-a-cri.html
 

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So then while neither are apparently completely accurate when it comes to led's, it would seem that the CCT does in fact not matter to much as long as the CRI is high enough.
I tend to look at it completely opposite.. CRI is meaningless while CCT tells me the "look" i.e blueish, yellowish ect..
The accuracy of "skin tones" or pastels is not that crucial..
But neither on their own nor paired is what is important to plants..

I'm pretty sure I could have an LED that has a high CRI but looks "off" to me..
Same w/ a say 6500k CCT light..

However, CRI is a poor indicator of the perception of light produced by LEDs, and scores as low as 25 can produce vivid-appearing white light, while high-scoring sources can still be very poor at rendering reds, including skin tones.
The top CREE on this page has a CRI of 90 @ a CCT of 2700.. Below is a "cooler" tank at 3000-3500K......NOT EXACTLY fair since the CREE is definitly "special" in some regards and would give a better showing.. I'd have to see them in action so to speak..




http://en.wikipedia.org/wiki/High_CRI_LED_Lighting

2700 K is equivalent to a standard incandescent light. Sunlight's color temperature is 5,780 K, but indoor lights with a color temperature this high will tend to look unnaturally blue to some. Generally any color temperature other than 2700K will look unnatural in a home setting until people become used to the higher color temperatures.[citation needed]
Another way to look at it throw a bunch of incandescent "light bulbs" (CRI = 100) over your tank. See what you think..
 

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So what you are saying is that neither CCT nor CRI mean anything and are not important when it comes to led's?
All i am looking to do really is to put together my BML light and have reached the point that i am ready to order but have received comments such as "well i hope you like blue because the main color in your spectrum is blue". which confused me as my CRI in said spectrum is 96. not sure how with a 96 CRI that things would look blue. I'm just confused.
First keep this always in mind. Sunlight always has a CRI of 100. It has that value before sunrise, at sunrise- sunset... It's easier to match sunlight by artificial means at either end of the day and create a light source that has a high CRI like you achieved. It is more challenging to create a high CRI at noon time. But with leds outputing many different wavelenghts of light it is possible to create a light source that matches noon time sunlight. How I approach it is by looking at the CRI vs the Color temperature. When I get a CRI of 98 yet still have a color temp of around but not above 6000K or below 5500k I am happy.

The best information indicate at the color temp of midday tropical sunlight to be 5740K. Most plants are from the tropics and those that are from temperate zones will grow just at well.

Color temp chart http://phys.org/news166945490.html
 
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