EEVblog #361 – LED Ceiling Panel Lighting 101Posted on September 28th, 2012 5 comments
How do LED ceiling panel LED lights work?
Everything you need to know about LED ceiling panel lighting, with Doug Ford.
And a bonus tutorial on underwater LED lighting.
Two more parts to this LED lighting installation coming soon…
Blue light in a pool – perhaps it has something to do with Rayleigh Scattering?
I wish there were more focus within the industry on creating better quality artificial light. With all due respects, I don’t find the current generation of LED lighting to be much better than fluorescent bulbs. A few years ago, I replaced all of my incandescent bulbs with daylight-balanced CFLs, and the result was that after a year, I noticed no significant change in my electric bill, and my vision was so messed up that I could no longer read printed books or other documents.
If LED lighting is better than that, than fine, replace all of the fluorescent bulbs! But I’m keeping my neodymium halogen bulbs as long as I can still buy them. The reason is that they are the closest thing to natural sunlight that I can find. My vision is recovering, and I can already read again.
Except for things that live deep in bedrock or the bottom of the ocean, virtually all life on Earth has evolved over the past 3.5 billion years or so to work with with sunlight. It is basically 5500-6000 degree Kelvin black body radiation with absorption bands from every natural element. If we use technology to replace that, we should try to match it, and not just trick ourselves with “daylight-balanced” lighting or similar, which fools the eye but does not provide anything like natural light.
Good engineering practices keep quality as the number one priority, and add low cost and other attractive criteria afterward. This is especially important with basic things such as food and light. It is not easy to create something at a price point, and design in quality later.
While writing this, I have the feeling some tempers may flare at my opinions. Sorry, but I have to say it.
My place is pretty much CFL free now. I’ve replaced most of them with LED bulbs (IKEA and Philips). They’re definitely on par or better and with the high energy costs over here, they will amortise within a year or so.
LED quality is an issue, especially which cheap ebay ones. I’ve seen die discoloration and noticeable shifts in emission wavelength. The somewhat expensive Nichia LEDs I used for another LED lamp haven’t shown any deterioration so far, but they run at much lower current and stay cooler.
I just want to confirm the suggestion of grunto: The blue light is scattered by Rayleigh scattering.
This are the important details (which I expect to be found in Wikipedia as well):
- The Rayleigh scattering goes proportional to the fourth power of the frequency. Therefore there is a big difference between red and blue (blue scatters therefore about 2^4=16 times stronger).
- Rayleigh scattering strength might change slightly with temperature, etc., but as the power 4 dependency is such strong, one does not recognize it as the relation between the scattered colors is staying same.
- The only chance to change the color distribution is to add a different scattering mechanism (e.g. pour milk into the pool ).
- The classic example for Rayleigh scattering is the sky. White light crossed the sky the blue parts are scattered perpendicular to the propagating, and the sky gets blue (without Rayleigh it would be black when there are no clouds). In the evening/morning, when the sun is quite low, it gets red, as all blue parts are scattered away. (Correspondingly the sea scatters blue, while red is passing to the depth.)
Well, I’m not physicist, but electronic engineer in the field of optical communication (or call it a RF engineer at 200 THz).
You’re so right, Jay Ts. I especially hate those cheap white car headlights that shine with a white bluer than daylight!
Daylight (our sun) color temperature is 5500-6000 Kelvin. An incandescent lightbulb has a color temperature of 2700-3300K; a candle flame, 1850K.
Cree’s white XLamp7090-XR-E LEDs come in three different categories–warm white, neutral white, and cool white.
warm white 2600-3700 K
neutral white 3700-5000 K
cool white 5000-10000K
Each of these categories is further divided into six “bins”. So when you design lights to illuminate large areas with white LEDs, you can order LEDs from the same “bin” for color uniformity.
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