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Author Topic: Use of White Lighting- Particularly LED  (Read 1270 times)
Lin
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« on: January 15, 2012, 08:59:23 AM »

http://www.sciencedaily.com/releases/2011/09/110912092554.htm
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« Reply #1 on: January 15, 2012, 11:46:58 AM »

Yeah, they had 2 rats in the study and placed a billion watts of white light inside their 6 inch long cage for 2 years... rats got sick... maybe from old age... but, hey! those lights had to cause it...
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« Reply #2 on: January 15, 2012, 12:13:42 PM »

I have no doubt of results::  nothing can replace sunlight.  It is hard to get enough sun time in today's work place or home enviorment.  I worked outside all my life.  Now retired I get blues in winter when we get string of cloudy days.  To much sun = skin cancer.     
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Lin
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« Reply #3 on: January 15, 2012, 12:58:36 PM »

Bob,

What you have is called Seasonal Affective Disorder (http://en.wikipedia.org/wiki/Seasonal_affective_disorder).  It is more common than most people realize.  The issue of white light at night may be something different.  I have always felt the white light at night was not natural.  We would have evolved having yellowish light when the sun went down; fires, candles, etc.  Our incandescent bulbs give off a similar tone.  I noticed that you said you used 3000 degrees kelvin color temperature for your ceiling.  Incandescent bulbs are about 2700, so you are getting pretty close.  That is in the range they call "warm white".  I use the compact florescent, but always get them in as low a color temperature as I can find; I think they are commonly available at 2800.  Just for information, I think that candle light is around 1500.
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« Reply #4 on: January 15, 2012, 01:19:29 PM »

Lin: my knowledge is only general. Thanks for more informed answer. The 6000  range seems harsh to me.   Bob
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Iceni John
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« Reply #5 on: January 15, 2012, 01:27:29 PM »

This article raises several questions to me.   Frankly, I'm surprised to see journalism like this from a website that appears to be focused towards science.

1.   OK, let's assume that "pure white" light reduces the body's production of melatonin.   Over a 24-hour period what actual difference does it make?   In other words, does the relatively small amount of artificial light at night have such a great effect, in relation to the presumably melatonin-supporting daylight that is the majority of the light we encounter?

2.   If in fact melatonin production is lower because of "pure white" light, wouldn't it be simple to take melatonin supplements?   They're cheap and (I hope) benign.

3.   It says that white artificial light is actually blue light, at between 450 to 500 nm.   Isn't white light a combination of all colors, so how can artificial white light be otherwise.   Light is light, whether it's natural or man-made.   Am I wrong here?   I'm wondering if this premise that artificial light is inherently more harmful than natural light is correct?   Or is the article talking only about this blue light, not true white light?

4.   The article also talks about light pollution.   This is an entirely different subject, and the exact spectrum of the polluting light is not mentioned, although it mentions street lighting which is a warmer white.   I'm guessing that most of it is not "pure white" light such as from LEDs.   Throwing this subject into the article is a red herring  -  did the writer intend to obfuscate the subject?

This whole subject is definitely interesting, but this article does it a disservice.   In practical terms, I don't think that any bus conversions that use "white" LEDs inside will significantly change the convertee's (sp?) melatonin production enough to make any noticable difference.   If one has SAD (I did when I lived in England, and this is one reason I chose to live in SoCal), maybe the use of LEDs is marginally pertinant, but for those folk without SADness does it make any difference at all?

John
« Last Edit: January 15, 2012, 04:50:50 PM by Iceni John » Logged

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Len Silva
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« Reply #6 on: January 15, 2012, 02:09:22 PM »

White lightning suppresses my melatonin too but it usually takes three or four for total suppression.
« Last Edit: January 15, 2012, 05:34:59 PM by Len Silva » Logged


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« Reply #7 on: January 15, 2012, 03:14:12 PM »

len, u got any for sale?
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« Reply #8 on: January 15, 2012, 07:12:20 PM »

John,
There is actually a lot of weight in what the article has to say regarding the differences between various white light sources, particurlarly LED's vs incandescent and/or sunlight., and their research is very likely accurate and relative.

The piece you probably don't understand is that "white" light as supplied to up by our sun (or an incandescent lamp) is a continuous spectrum of light  comprised of all colors or wavelengths of light..  

These light sources are called "black bodies", which basically describes black things that are so hot that they emits visible (and invisible) light... The ratio of bluish light to reddish light that they emit has to do with how hot they are- that's where the kelvin temperature comes in.  Hotter (higher kelvin temperature) equates to light that is visibly bluer, but in all cases if you put the light from a black body source through a prism, you'll see a continuous rainbow of all colors making up that "white" light.
That's what we as humans have gotten used to over the last few million years, and what our bodies are programmed to react to.



LED's on the other hand, are devices that emit very specific, almost single wavelengths of light.  For example take an incandescent lamp and stick a red gel over it to make red light.
If you put that light through a prism you will see a broad spectrum of light.  But put the light from a red LED that "looks" to be the same color through that prism and you'll see only one narrow band of color.  Take a look at this graph... the yellow line shows the spectrum of a light bulb filtered by a red gel, which is a fairly constant spread of wavelengths between 600 and 750nm.  But the LED which "looks" the same is only a very narrow band of light centered around 635nm or so.

That is what these guys are talking about.

Light that is perceived as white, made with LED's, is actually missing most of the wavelengths that a similar white from the sun would contain.  All you have to do to make a human think light is white is add narrow bands of red, green, and blue together.  Interestingly you can also create a good looking "white" light using only blue and yellow... there are actually quite a few combinations of narrow bands that will look white to a human and still be missing most of what the white light from the sun or an incandescent light contains.

It's kinda like perfumes.  If you have a good smelling rose and you analyze the actual chemical constituents of it, you'll find that there are 5-6 major chemicals that make up roses' scent, along with almost three hundred minor chemicals.
  To make a synthetic rose scent, all you need to do is add those 5-6 major chemicals together in the right ratios, and leave out the hundreds of minor chemicals.  If you smell the two, they both smell like roses but there's something definitely different about that synthetic, and usually not as good. The "finesse" of the scent has been eliminated.

This chart shows the wavelengths of various lights that we're used to seeing, and other than the bar-code laser, most of the others can roughly be perceived by us as white light.
Its interesting to see how very different they are!



As the article states, LED white light is actually VERY blue.  There is no such thing as an actual white LED... what they are is a very intense blue LED with some phosphor painted over it. The blue light excites the phosphor to glow and produce yellowish light, and that plus what blue leaks through adds up in our eyes to look white.  "White LED's" can also be created by sticking a red led chip, a blue led chip and a green led chip into the same package. The result is an led that allows you to create any perceptual color, just like a TV or computer monitor does, by changing the ratios of light coming from those three chips.
 

Here's a couple of good articles on color Led's and light if you're interested... also where I got the graphs...
http://tinyurl.com/775bsuc
http://www.olympusmicro.com/primer/lightandcolor/lightsourcesintro.html
 

The LED industry has all the same problems... how to get these narrow band devices to fake us out and make us think it looks like real white light.

In the end, as the article states, we may get faked out and think what we're seeing is white light, but our melatonin sensors don't.  It's still not pinned down if this is good or bad for us, but it is real, and it probably has repercussions in the long run.

For what it's worth, I have changed most of my house and all of my shop to white LED lighting.  I think it's fantastic... science or not, I get along fine with it!!
« Last Edit: January 15, 2012, 07:26:47 PM by boogiethecat » Logged

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« Reply #9 on: January 15, 2012, 07:34:34 PM »

 I have white LEDs and will buy more, if needed. Presently have 24 or more in use in the bus. Also have been to Q several times recently, sittin 30 miles east of it.
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« Reply #10 on: January 15, 2012, 09:29:53 PM »

  What if the white (blue) led's were indirectly lighting the ceiling or wall that was a softer color, off white??
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Iceni John
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« Reply #11 on: January 15, 2012, 10:14:52 PM »

Thanks, Boogiethecat, now I know!   This forum's amazing  -  there's always someone who can explain the what and why behind the story.   Melatonin or not, I think most of us will still choose LEDs because of their lower power consumption;  maybe they'll also evolve in a few years to more closely mimic natural light.

John
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« Reply #12 on: January 16, 2012, 03:00:50 AM »

As a manufacturer of LED based solar simulators, I can say that white LED's cover the broadband visible spectrum fairly well, check the third graph. There is a low point around 500nM (cyan) and if you use white or warm white there will be a bump in red intensity. While it is fairly easy to match the visible solar spectrum using LED's, anything outside the 400-700 nM range is problematic. Matching solar intensity is another story.
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