http://ledsreview.com en http://backend.userland.com/rss2 Thu, 29 Jul 2010 04:16:57 -0700 More...]]> http://ledsreview.com/blogs/editors/25.php http://ledsreview.com/blogs/editors/25.php Wed, 01 Dec 2010 21:14:53 -0800
Kevin writes in his blog:

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I will be developing a few wall and pendant products as the inspiration leads me. Of course in the course of one week, engineering documentation will be only what I need to execute the prototype, using Rhino CAD to lay out 3D models before making chips, and there will be no UL listing. However, every design will be completed by me including design, engineering, machining, fab, and finishing - which is a lot of fun.
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The first weeks design is already complete and posted with details here.

Specifications
24"L x 20"H x 6"W. Utilizes Lynk Labs 12VAC Tesla LEDs on 12" 12W SnapBrite strip with SnapDriver power supply. The reflector/heat sink extrusion was also provided by Lynk Labs. Custom on-off switch. Black wrinkle body, tumbled aluminum with clear coat, and matte white finishes. All finishes are powder coat.



All of the designs will be made available for sale to fund future work on the project through the Lumenique Product Center for anyone interested.

Nice New Year Resolution, Kevin. Good luck!
More...]]> http://ledsreview.com/blogs/editors/24.php http://ledsreview.com/blogs/editors/24.php Tue, 01 Jun 2010 19:30:48 -0700 Aixtron reported delivery of their CRIUS® MOCVD system in a 7x4 inch configuration to SemiLEDs. It will be the first 4-inch LED chip line at SemiLEDs' production facility in Taiwan.

Do you know other companies already using 4-inch wafers for HB LED chips?
More...]]> http://ledsreview.com/blogs/editors/23.php http://ledsreview.com/blogs/editors/23.php Wed, 12 May 2010 09:11:04 -0700 Philips, Osram recently announced commercial availability of its ORBEOS CDW-031 OLED panel .




Diameter of the light output area is 79.00 mm (approx. 3"), the luminous efficacy at 186 mA is typically 23 lm/W. At 186 mA, the time to half luminance (L50) is 5,000hrs. Lifetime is strongly dependent on operating current: at 93 mA the L50 is 10,000 hours, and at 47 mA, 15,000 hrs. The tile is a little over 3 in. in diameter (80mm). Data sheet.

With significantly lower efficacy than HB LEDs and exorbitant prices I liked someones note on the subject:

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Is OSRAM planning for these OLEDs to be sold in the organics aisle of grocery stores?
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More...]]> http://ledsreview.com/blogs/editors/22.php http://ledsreview.com/blogs/editors/22.php Fri, 12 Mar 2010 18:42:45 -0800 new labels for light bulbs based on light output rather than energy consumption.

The Lighting Facts label would provide information about brightness, energy cost, the bulb's expected life, color temperature (for example, whether the bulb provides "warm" or "cool" light), as well as wattage. The label also would require disclosures for bulbs containing mercury. The bulb's output in lumens—and a mercury disclosure for bulbs that contain mercury—would also have to be placed on the bulb itself.


The Notice of Proposed Rulemaking was published Nov. 10, and comments on the change are being accepted through Dec. 28.

I'd love to hear your thoughts on the proposed changes. Do you think it will make it easier for consumers to pick out energy-efficient bulbs or will it just confuse them more?
More...]]> http://ledsreview.com/blogs/editors/21.php http://ledsreview.com/blogs/editors/21.php Fri, 12 Feb 2010 22:37:27 -0800
1 - intensity profile

It's simply the graph showing the light intensity vs. the angle. It can be displayed either in Cartesian or in polar coordinates. This graph usually appears in all reliable LED's specifications.


2 - intensity profile of LEDs dice

The emitted light fr om the die itself (without any optics) is usually very close to a Lambertian emission. Nice word, but what does it mean?
A Lambertian emission (http://en.wikipedia.org/wiki/Lambert%27s_cosine_law) refers to a source emitting the same quantity of light in all directions. When you look at this source, the quantity of light (intensity) you will see is proportional to the seen surface. And this seen surface is equal to S.cos(teta) where S is the total surface of the source, and teta the viewing angle.

Now we know why the intensity profile of a die without optics is a cosine curve, as simple as that!

Another interesting equation to know is the power emitted by a Lambertian source within a given cone:



Where P0 is the total power emitted by the LED and phi the half-angle of the cone.


Finally, let’s calculate the intensity of a die for small angle cones, normal to the surface:




3 – adding optics to the die…

The optics integrated in the encapsulated LEDs is usually intended to collimate the light (send all the rays towards a parallel direction). Light that should have gone to the sides is now redirected to the center. The intensity graph is therefore changed so that the intensity is stronger at the center (teta=0), but at the price of a reduced intensity on the sides (the integrals of both curves, before and after the lens, are of course equal).

Let’s calculate now the intensity of the system LED + optics, wh ere the optics collimates 50% of the energy within a +/-3deg cone:




And for a system collimating 30% of the light within +/-1deg cone:



which is 1000 times (!) stronger than the original intensity without lens!

Thus, a significantly weak LED can exhibit a much higher intensity value than real power LEDs, only with the use of a simple lens. It sometimes seems to be a method to artificially enhance the power (and the sales to those who are not “skilled in the art”) of old and low-power LEDs.


Conclusion: NEVER USE THE INTENSITY VALUE (CANDELA) TO COMPARE THE TOTAL POWER EMITTED BY LEDS.


More...]]> http://ledsreview.com/blogs/Elie/20.php http://ledsreview.com/blogs/Elie/20.php Fri, 11 Mar 2011 10:10:10 -0800

Luxeon I emitters are obsolete now. LED lighting pioneers either have to redesign their products or they can turn to Avago which offers cross-reference parts.



Luxeon I emitters were the top technology few years ago. But I think it's time to move on.


More...]]> http://ledsreview.com/blogs/editors/19.php http://ledsreview.com/blogs/editors/19.php Fri, 11 Jun 2010 09:19:31 -0700 candela.

We have first to remember an old story from school: the solid angle. Roughly, it can be compared to “3D angle”; Wikipedia (http://en.wikipedia.org/wiki/Solid_angle) describes it as a “measure of how large an object appears to an observer”. And in the same way that “2D angles” do not have physical units but are still measured in degrees or radians, the solid angle has no physical unit and is measured in steradian (abbreviation: sr). The most useful equation to remember is, by far, the solid angle of a cone:



And the 2 values to remember are:
- the solid angle of an entire sphere:

- the solid angle of a half-sphere:



And now, back to our candela: the “light intensity” is the quantity of photons passing through a given solid angle. The units are W/sr in radiometric system, and lumen/sr in photometric system. The latter is also called candela.

In a LED’s specification, this value is intended to tell you how much light is directed in the LED-axis direction.

Seems easy, isn’t it? Next time, we will speak about optics and intensity diagram, and you will understand why this parameter is so much misleading if you don’t use it properly…



More...]]> http://ledsreview.com/blogs/Elie/18.php http://ledsreview.com/blogs/Elie/18.php Sun, 11 Apr 2010 23:40:32 -0700 important item in a LED specification is also the most obscure one: this is the “Optical Power”. It seems that the LEDs’ manufacturers do it on purpose to confuse their customers! How can you compare the emitted energy when it’s called sometimes “Watt”, other times “Lumen” or “Candela”??? Isn’t it like searching the most beautiful woman with deforming glasses???

Let’s put all this in order, and let’s remember:

1 – there are 2 scales for optical power measurement:

a) radiometric scale (units: WATT): this is the absolute and objective scale (my preferred one!). It’s simply proportional to the number of photons and their energy!

b) photometric scale (units: LUMEN): this is the physiological and subjective scale, the sensitivity of your eyes. In other words, how strong YOU will see the light.



2 - The sensitivity of the eyes does not depend on their color, but on the wavelength of the light reaching them. As you may know, the eyes are the most sensitive to green, less sensitive to blue and red, and blind to UV and IR.
So, how can I compare radiometric and photometric scales? The following graph is the conversion from Lumen to Watt. Let’s take the red dot as an example: 350 lumen at 610 nm are equal to 1 watt. Easy, isn’t it?



3 – Quiz
question 1: how does it make sense that the UV that burns your skin and your eyes is as strong as 0.0 lumen?
question 2: Take a blue LED that emits 1 lumen. Cover it with phosphor. This LED emits now 10 lumen. Did we discover the optical perpetuum mobile (source of perpetual energy)???


More...]]> http://ledsreview.com/blogs/Elie/17.php http://ledsreview.com/blogs/Elie/17.php Wed, 11 Mar 2009 08:23:29 -0700 http://ledsreview.com/articles/256/ Since then, specifications got better, especially efficacy and CRI. I like these modules for simplicity and build quality. Read full review later this month.


Transcend RM2


Transcend PM3
More...]]> http://ledsreview.com/blogs/editors/16.php http://ledsreview.com/blogs/editors/16.php Wed, 11 Feb 2009 09:46:17 -0800