# Poll: Color vs Brightness



## OhMyGosh (Jul 12, 2007)

I believe we will soon see flashlights with 'warmer' color that is more like incandescents. They are generally a bit less bright than the 'cool-white' LED's in most current lights.

If the warm light is 25% less bright, which would you prefer?


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## easilyled (Jul 12, 2007)

You have loaded this poll so that a warmer tint is seen as being desirable.

There are many of us who prefer tint to be as neutral as possible.

I would willingly trade a little brightness for *less* yellow tint.

However I can't vote for this since there is no option for this.

With Cree, for instance many would prefer a WC Q4 to a WG Q5 because
the WC is nearer to what the majority of us perceive as pure white whereas
the WG is yellow-green.

If you don't change your poll and the wording to also record those that
prefer the other way round its worthless in my humble opinion.


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## OhMyGosh (Jul 12, 2007)

Well sorry. I had intended for the second choice to be a neutral white but with reduced 'blueness'. You can achieve this by adding filters BTW. I guess I didn't word it very well. I don't think you can edit poll choices once it starts.

Still the point of the poll is in the title. Do you feel that LED flashlights need to be brighter in general? Or have they become bright enough where improving the color quality is more important than increasing the brightness. I just kind of wonder which side of that fence people are leaning toward.


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## easilyled (Jul 12, 2007)

No problem! Its an interesting question. 

It seems to me like you only need two voting options to achieve your intentions. ie.

1) I always prefer brightness, no matter what tint.

2) I am prepared to sacrifice brightness for the tint I prefer the most.


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## 2xTrinity (Jul 12, 2007)

I would like an LED that would be "warmer" than the typical phosphor LED, but _not_ warm like incandescent, which is way too far in the other direction. I prefer neutral white lighting if at all possible. However, color temperature is not the only issue. LEDs could remain as "cool" as they are today, yet still benefit from a more balanced spectrum -- high quality 6500K fluorescent tubes for example render color MUCH better than most phosphor LEDs because their spectrum is more balanced, even at the same color temperature. 

Essentially what I would find ideal would be something right in between incandescent and current LEDs -- about 4200K color temperature, but with high color rendering. This has already been done in prototypes by using a blue die, with separate red and green phosphor emissions, rather than blue + yellow green.

4500K with fairly high color rendering can also be created by selecting LED bins that have a slight yellow-green tint to them, like Cree WH, and augmenting them with separate red emitters (the result of which is a mixture that is to my eyes noticeably warmer than a 5000K fluorescent tube, yet cooler than a 4100K tube, hence my estimate of 4500K) Adding the red though really makes a difference in that it drastically improves color rendering by filling in a gaping hole in the spectrum. Another point worthy of noting is the drop in efficiency by doing this is almost insignificant (one Red LuxIII LED driven at half strength will correct about 5 Cree's at full power), yet the improvement is highly dramatic.

The weak red output in current LEDs though is something that filtering cannot fix. Filtering can be used to soften LEDs that are excessively blue, but there is a limit. While I find I can get most LEDs to match Cree WH bins, any stronger filtering than that causes the output to look green.


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## AndyTiedye (Jul 13, 2007)

Color! Bring on the super-bright RGBs!


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## SemiMan (Jul 14, 2007)

Why would I want super-bright RGB? An RGB light source does not give good color rendering. A good phosphor converted white actually has better color rendering than an RGB source. Accurate color rendering is essentially based around the ability to make things look a similar color as they would under sun light. Sunlight is a very broad spectrum source. 3 very narrow colors can not be expected to behave similarly. You can trick the eye into believing that the light emitted directly from an RGB source is very close to any color of white you wish, however, it is a completely different story when you start reflecting that RGB LED off objects. Some tests have shown that in order to do very good color rendering with monochrome LEDs requires 5 different color of LEDS.

Semiman


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## SemiMan (Jul 14, 2007)

Oh, my vote is for the new Neutral White LEDs which appear to be coming out in almost the same brightness levels as the cool whites..... at least outdoors. Similar to 4K HID, they render the natural reds and greens we see outside better than 6K LEDs. However, if I am doing fine work, I will take the 6K LEDs. They seem to be better for visual acuity.

Semiman


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## Martini (Jul 15, 2007)

The published specs for the Luxeon Rebel indicate that the cool white and neutral white LEDs have the _same output_; i.e., we get warmer tint and lose _nothing_. I have to wonder what the actual spectrum of these neutral whites will be, but they have a CCT of 4100k (according to Luxeon). Sounds perfect to me.


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## 2xTrinity (Jul 15, 2007)

Martini said:


> The published specs for the Luxeon Rebel indicate that the cool white and neutral white LEDs have the _same output_; i.e., we get warmer tint and lose _nothing_. I have to wonder what the actual spectrum of these neutral whites will be, but they have a CCT of 4100k (according to Luxeon). Sounds perfect to me.


There is no reason that neutral color temperature should be dimmer. If anything, it should be brighter because the eye is much more sensitive to yellow/green light emitted by the phosphor than blue light. This is why standard 4100K fluorescents produce more lumens/watt than daylight fluorescent which have a higher ratio of blue phosphor. In the case of LEDs, there's likely a mitigating factor in that converting more blue light into yellow/green using phosphor will require a thicker layer of phosphor, which may impede light extraction. However, if the extraction issue could be overcome, I believe the neutral LEDs would actually be _more_ efficient than the cool LEDs.

As far as doing a neutral white LED with only one phosphor, I expect this result in a spectrum similar to both 4200K HIDs, which for the most part render yellows and greens (such as foliage) quite well, but are slightly deficient at rendering saturated reds and blues. An actual dual phosphor neutral white LED on the other hand could be quite amazing -- no deficiency in spectrum whatsoever, and perfectly neutral color temp. I read an abstract once about a biphosphor LED with CCT of 4000K and CRI exceeding 95, I would totally love to be able to buy accent spotlights with those specifications.


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## lamperich (Jul 16, 2007)

since I held a yellow color filter in front of my 
coolwhite torchs and light up a shrub
it was significant dimmer but as Trinity already wrote
for me it was easy to discern what is green and what is brown.

when i take a look in the cree datasheet..
www.cree.com/products/pdf/XLamp7090XR-E.pdf Page 4
it looks pretty promising.

Therefore am really keen on neutral white LEDs
and the first real life reviews )


P.S. it´s a good feeling iam not alone with this "problem"


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## OhMyGosh (Jul 17, 2007)

Interesting that people seem to be pretty evenly split so far between want more light and wanting a better color - whatever that color may be.

Has anyone done any tests for adding a red LED to cool white? I wonder just how much red you need. My off the cuff guess would be 1 red for 3 white would improve things a lot. This is a major reason I like the Rebel, it's small size lends itself to multiple emitters in a single optic. Also a number of colors are now available.


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