AAC Book Error - LEDs

Discussion in 'Feedback and Suggestions' started by Wendy, Oct 22, 2008.

  1. Wendy

    Thread Starter Moderator

    Mar 24, 2008
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    This section:

    http://www.allaboutcircuits.com/vol_3/chpt_3/12.html

    This chapter:

    Yellow LEDs were developed about the same time as red and green. They can also be created with red/green bidirectional LEDs, but they are also a stand alone color, a very old one at that.

    The chapter mentions it, but I can't help feeling that some distinction should be made between older models and new LEDs, since the physics between them is slightly different. LEDs are a hard one to keep up with, as the field is currently (still) in a constant state of flux, but the differences between the older, dimmer LEDs are pretty profound (lower voltage drop, differences in physical construction, slightly different physics,among other things). The newer LEDs use internal mirrors (I'm not sure of the exact arrangement) to boost efficiencies.
     
    Last edited: Oct 22, 2008
  2. Dave

    Retired Moderator

    Nov 17, 2003
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    Bill, apologies for the late reply, I have been off-line for a couple of days

    If correct, then I think it is worth removing ambiguity in the fact that this article implies that Yellow is (only) constructed from a combination of Red/Green instead of being a stand alone colour. Do you have a source for this that I can have a look at?

    Also, with regards to distinction with older technology, the question we must ask is how relevant is the older technology to today's technology? We need to draw a line between detail and the potential for saying too much - I would be interested in your insight into the above question. Thanks.

    Dave
     
  3. bertus

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  4. Wendy

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    I was referring to this article in Wikipedia, which is a bit more comprehensive...

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

    I was playing with Yellow LEDs as early as the 70's. They were a bit easier to burn out, but there was no doubt about their color.

    The new LEDs can go well over an amp, quite different from the early models. I learned that the hard way at this site, made a fool of myself I did. The brightnesses are several orders of magnitude, maybe more, and there is a definite difference in voltage drops. I'm weak on this I believe some of the underlying physics is a bit different.
     
    Last edited: Oct 26, 2008
  5. Wendy

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    Here is another source that documents LED colors over time, and clearly states yellow was available during the 70's.

    http://www.marktechopto.com/Engineering-Services/history-of-leds-and-led-technology.cfm

    Rereading the LED article, no mention is made of the new high current devices (700ma-1.5A).

    The question is, will there be an update and who will do it? I'll volunteer my services, such as they are, but I don't want to impose.
     
  6. Dave

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    Thanks for all the links, this one certainly adds context to the original query.

    Please do Bill, we could look at clearing an ambiguities in the AAC article.

    Can I make the following recommendation? This is a sub-section of a wider article so conciseness is paramount, so we need to ensure the text is not substantially more verbose than what is already there. If you can draw up a revision then we can look at where we go from there. I think bringing the article "up to date" should be the key making reference to the newer high-current devices.

    Thanks for your help.

    Dave
     
  7. Wendy

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    First draft:

    Diodes made from a combination of the elements gallium, arsenic, and phosphorus (called gallium-arsenide-phosphide) glow bright red, and are some of the most common LEDs manufactured. By altering the chemical constituency of the PN junction, different colors may be obtained. Some of the currently available colors other than red are green, blue, and infra-red (invisible light at a frequency lower than red). Other colors may be obtained by combining two or more primary-color (red, green, and blue) LEDs together in the same package, sharing the same optical lens. For instance, a yellow LED may be made by merging a red LED with a green LED.

    ---------------------------------------------------

    Diodes made from a combination of the elements gallium, arsenic, and phosphorus (called gallium-arsenide-phosphide) glow bright red, and are some of the most common LEDs manufactured. By altering the chemical constituency of the PN junction, different colors may be obtained. Early generations of LEDs were red, green, yellow, orange, and infra-red, later generations included blue and ultraviolet, with violet being the latest color added to the selection. Other colors may be obtained by combining two or more primary-color LEDs together in the same package, sharing the same optical lens. This allowed for multicolor LEDs, such as tricolor LEDs (commercially available in the 1980’s) using red and green (which can create yellow) and later RGB LEDs (red, green, and blue), which cover the entire color spectrum.

    ----------------------------------------------------
    ----------------------------------------------------

    A white LED is a blue LED exciting a phosphor which emits yellow light. The blue plus yellow approximates white light. The nature of the phosphor determines the characteristics of the light. A red phosphor may be added to improve the quality of the yellow plus blue mixture at the expense of efficiency. Table above compares white illumination LEDs to expected future devices and other conventional lamps. Efficiency is measured in lumens of light output per watt of input power. If the 50 lumens/watt device can be improved to 100 lumens/watt, white LEDs will be comparable to compact fluorescent lamps in efficiency.

    <add on> -------------------------------------------------------

    LEDs in general have been a major subject of R&D since the 1960’s. Because of this it is impractical to cover all geometries, chemistries, and characteristics that have been created over the decades. The early devices were relatively dim and took moderate currents. The efficiencies have been improved in later generations to the point it is hazardous to look closely directly into an illuminated LED, resulting in eye damage, with only a minor increase in dropping voltage (Vf) and current. Modern high intensity devices have reached 1800 lumens using 0.7Amps (820 lumens/watt), and even higher intensity models can use even higher currents with a corresponding increase in brightness. Other developments, such as quantum dots, are the subject of current research, so expect to see new things for these devices in the future.
     
    Last edited: Nov 26, 2008
  8. Dave

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    I think the changes add clarity. I cannot recommend further changes in this part.

    This is "as-is" from the e-book, right?

    Is this addition to go at the end of the LED sub-section?

    Dave
     
  9. Wendy

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    Yep.

    I was thinking it added a certain amount of context. Otherwise, in 5 or so years someone else will be point out the now commercial LEQD LEDs (I made this up, Laser Excited Quantum Dots), or some such. LEDs are probably going to be changing for quite some time.

    The LED musium was interesting reading, it could be argued LEDs were around before incandesent bulbs, but no one saw the potential. It was blue, of all colors.

    BTW, for the book, do we use Queens English or American spelling? I've been assuming American, and we all know what assuming means.
     
    Last edited: Oct 30, 2008
  10. Dave

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    Thanks, just wanted to make sure there wasn't a subtle edit I hadn't picked up.

    The highlighted bit doesn't read right:

    - "closely directly" should at least be "closely and directly".

    - The part with "resulting in eye damage" and "with only a minor increase.." appears to be describing two things without being clear on either. Ok, I know the point it is trying to say, but it needs making clearer with respect to the opening part of the sentence.

    Other than that the rest of this part is fine.

    US English is the standard because that is the spelling-type the original author, Tony Kuphaldt, wrote in.

    Dave
     
  11. Wendy

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    Good enough, it was the first draft, how about...

    LEDs in general have been a major subject of R&D since the 1960’s. Because of this it is impractical to cover all geometries, chemistries, and characteristics that have been created over the decades. The early devices were relatively dim and took moderate currents. The efficiencies have been improved in later generations to the point it is hazardous to look closely and directly into an illuminated LED. This can result in eye damage, and the LEDs only required a minor increase in dropping voltage (Vf) and current. Modern high intensity devices have reached 180 lumens using 0.7Amps (82 lumens/watt, Luxeon Rebel series cool white), and even higher intensity models can use even higher currents with a corresponding increase in brightness. They are expensive, but costs are dropping. Other developments, such as quantum dots, are the subject of current research, so expect to see new things for these devices in the future.

    *********************

    That last part, "They are expensive, but costs are dropping.", might be better left out. Who knows where costs will be in 5 years?
     
    Last edited: Nov 1, 2008
  12. scubasteve_911

    Senior Member

    Dec 27, 2007
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    I believe this is called "extrapolation" and is a legitimate statement. It boils down to a toss-up, do you want to be wrong if the prices do not go down?, or, do you want readers to know LEDs are a good lighting solution that is becoming more and more cost effective?

    Steve
     
  13. Wendy

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    Perhaps, but this is for a educational text book, also a reference. I didn't know LEDs had changed so much, which is why I felt the last paragraph was necessary.

    As I understand it, Dennis is the current editor, with Dave's help. Dave helps filter the slush. I was just telling Dave I wasn't sure if it belonged or not, so he could be the abitrator.

    I'd like to see the AAC book finished, maintaining the high quality it already has. I'm very happy that I can contribute, it's not often people can make a difference. The fact that this is open source (or pretty close) means it can be updated indefinately, so it could be around for a very long time, unlike a lot of reference material.

    I'm not a writer, but I would like to be. This is an opportunity to practice a new skill set.
     
    Last edited: Nov 1, 2008
  14. Wendy

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    I've also touched up the drawing to show the internal cathode. Don't know if Dennis and you like it better or not, but here is the offering...

    Original:

    [​IMG]

    LED, Light Emitting Diode: (a) schematic symbol. (b) Flat side and short lead of device correspond to cathode. (c) Cross section of Led die.

    Modified:
    [​IMG]

    LED, Light Emitting Diode: (a) schematic symbol. (b) Flat side and short lead of device correspond to cathode, as well as the internal arrangement of the cathode. (c) Cross section of Led die.
     
    Last edited: Nov 3, 2008
  15. Dave

    Retired Moderator

    Nov 17, 2003
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    The revision is much clearer Bill. I would say the "broken-down" style is preferential in other work you do on this project.

    Can I ask, is 1800 lumens at 0.7Amps for modern high intensity devices expressed as a typical value? The reason I ask is that the statement "Modern high intensity devices have reached 180 lumens using 0.7Amps (82 lumens/watt, Luxeon Rebel series cool white)" gives the implication that this is not so much a nominal value. If it is a typical value I would recommend the line by tweaked to:

    The subsequent line flows much better as a result.

    I am also of the opinion that the statement of costs decreasing is superfluous to the general premise of the text; therefore that line is best dropped.

    Dave
     
  16. Dave

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    Subtle change is nice Bill, I will leave it to Dennis to approve the change.

    Dave
     
  17. Wendy

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    Original:

    [​IMG]

    LED, Light Emitting Diode: (a) schematic symbol. (b) Flat side and short lead of device correspond to cathode. (c) Cross section of Led die.

    Modified:
    [​IMG]

    LED, Light Emitting Diode: (a) schematic symbol. (b) Flat side and short lead of device correspond to cathode, as well as the internal arrangement of the cathode. (c) Cross section of Led die.

    ---------------------------------------------

    <before>

    Diodes made from a combination of the elements gallium, arsenic, and phosphorus (called gallium-arsenide-phosphide) glow bright red, and are some of the most common LEDs manufactured. By altering the chemical constituency of the PN junction, different colors may be obtained. Some of the currently available colors other than red are green, blue, and infra-red (invisible light at a frequency lower than red). Other colors may be obtained by combining two or more primary-color (red, green, and blue) LEDs together in the same package, sharing the same optical lens. For instance, a yellow LED may be made by merging a red LED with a green LED.


    <after>

    Diodes made from a combination of the elements gallium, arsenic, and phosphorus (called gallium-arsenide-phosphide) glow bright red, and are some of the most common LEDs manufactured. By altering the chemical constituency of the PN junction, different colors may be obtained. Early generations of LEDs were red, green, yellow, orange, and infra-red, later generations included blue and ultraviolet, with violet being the latest color added to the selection. Other colors may be obtained by combining two or more primary-color LEDs together in the same package, sharing the same optical lens. This allowed for multicolor LEDs, such as tricolor LEDs (commercially available in the 1980’s) using red and green (which can create yellow) and later RGB LEDs (red, green, and blue), which cover the entire color spectrum.

    ------------------

    <before>

    A white LED is a blue LED exciting a phosphor which emits yellow light. The blue plus yellow approximates white light. The nature of the phosphor determines the characteristics of the light. A red phosphor may be added to improve the quality of the yellow plus blue mixture at the expense of efficiency. Table above compares white illumination LEDs to expected future devices and other conventional lamps. Efficiency is measured in lumens of light output per watt of input power. If the 50 lumens/watt device can be improved to 100 lumens/watt, white LEDs will be comparable to compact fluorescent lamps in efficiency.

    <after>

    A white LED is a blue LED exciting a phosphor which emits yellow light. The blue plus yellow approximates white light. The nature of the phosphor determines the characteristics of the light. A red phosphor may be added to improve the quality of the yellow plus blue mixture at the expense of efficiency. Table above compares white illumination LEDs to expected future devices and other conventional lamps. Efficiency is measured in lumens of light output per watt of input power. If the 50 lumens/watt device can be improved to 100 lumens/watt, white LEDs will be comparable to compact fluorescent lamps in efficiency.

    LEDs in general have been a major subject of R&D since the 1960’s. Because of this it is impractical to cover all geometries, chemistries, and characteristics that have been created over the decades. The early devices were relatively dim and took moderate currents. The efficiencies have been improved in later generations to the point it is hazardous to look closely and directly into an illuminated LED. This can result in eye damage, and the LEDs only required a minor increase in dropping voltage (Vf) and current. Modern high intensity devices have reached 180 lumens using 0.7Amps (82 lumens/watt, Luxeon Rebel series cool white), and even higher intensity models can use even higher currents with a corresponding increase in brightness. Other developments, such as quantum dots, are the subject of current research, so expect to see new things for these devices in the future
     
    Last edited: Dec 12, 2008
  18. Wendy

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    I decided to leave the "have typically" off because I don't think these LEDs are typical, not at $30 a pop. They have some really strange cut dies looking at the website, and these are among the top of the line components. I think these specs are transitory, there will be better in the near future, but for now it's the best money can buy.

    Any further changes (I hope it is finished) I will modify the above post for simplicity.
     
  19. Dcrunkilton

    E-book Co-ordinator

    Jul 31, 2004
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    Thanks all,

    Thanks for the changes, which have been entered at ibiblio.

    Dennis
     
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