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LED Types of 2015

Discussion in 'LEDs and Optoelectronics' started by threetwothree, Jul 23, 2015.

  1. threetwothree

    threetwothree

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    Jul 23, 2015
    Hey guys,

    Does anyone know where I can find a good catalogue, or website, or some sort of online listing of what's avaliable in LEDs as of today?

    I'm starting a new project and want to look at the different range of LEDs I can use to match perfectly with the rest of my circuit, but I don't know where to start looking.

    I went to the local electronics store today (Jaycar in ringwood for those of you playing at home in Melbourne, Australia), and after a while of speakin with the bloke behind the counter (who gave me so much helpful info, absolute legend), I realised there are other types out there as I wanted one brighter than their brightest 5mm LED, and they had a "Luxeon Star LED"

    So basically, I want to know of other types that have a higher Vf or work more efficiently etc., for example like the Luxeo Star, or some crazy SMD's...

    I'm fairly amatuer to all this if you can't tell

    Cheers :)
     
  2. Martaine2005

    Martaine2005

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    May 12, 2015
    Hi,
    If I was you I would just type LED into your favourite search engine and click on IMAGES.

    Then spend hours or days reading all the different site information.

    Martin
     
    davenn likes this.
  3. Colin Mitchell

    Colin Mitchell

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    Aug 31, 2014
    High wattage LEDs simply take more current and you finish up with enormous heatsinking problems with how to get rid of 50 watts of heat.
     
  4. Gryd3

    Gryd3

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    875
    Jun 25, 2014
    Well.. here's where it gets a little complicated.
    High power LEDs... like the 50Watt and 100Watt that you find online are actually just an array of LED dies stuffed onto the same board.
    Typically what happens, is the forward voltage of 3.7v for white LEDs example will increase in multiples as the LED package adds more dies in series up to a point, then they will then begin to put more LED dies in parallel.

    So, for sake of explenation... you can get LEDs in a variety of shapes... round, square, square and flat with a little dome on top. 3mm, 5mm lenses. Varying degrees of brightness.
    Look at those first... and if you want a LOT of brightness, then investigate 'high power' leds.

    Best of luck ;)
    (You may have an easier time if you give us an example project or look at existing projects online)
     
  5. threetwothree

    threetwothree

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    0
    Jul 23, 2015
    I'll give you a criteria of the LEDs characteristics which I want to use, and by the way, i really appreciate the answers guys, every bit of information i get is one step closer to my understanding as a whole and it starts to piece together like a puzzel

    Anyway, this is how I would like it to peform:
    Lumen: >100
    Light output: Beam as concentrated and directional as possible
    Vf: <4V

    Does something like this exist out there?
     
  6. Gryd3

    Gryd3

    4,098
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    Jun 25, 2014

    They certainly do!
    You can get your hands on a 3Watt LED, or go all out and buy a higher power LED array.
    To make them directional, buy a lens, or a reflector. ;)
     
  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,169
    2,685
    Jan 21, 2010
    100 lumens is not a lot, you should be able to get that from a single high power LED.

    To concentrate the beam, you'd be looking at having a lens in front of it (reflectors are pretty useless because the LED doesn't emit much light sideways, and none to speak of backwards.

    asking for <4V indicates to me that you need to read the LED tutorial :) A single white LED will have a Vf around 3.7 to 4.0 volts, but you drive LEDs from a current source, so within reason, the exact value doesn't matter a great deal (as long as it's less than your power supply less losses.
     
  8. threetwothree

    threetwothree

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    Jul 23, 2015
    Yeah I'm thinking a lens is the way I'll have to go, but I've got a size constraint I need to deal with so the directional beam pattern of the LED alone ay have to suffice!

    I'm checking out that video now.


    I've got a small keyring torch here which i've disected and measured with a multimeter and these are the values I obtain.
    [​IMG]
    1. What would be the reason I measure 3.3V across the LED, yet they are very bright, and are white in colour? This is what made me believe there must be other types of more efficient LED's out there which can operate within different parameters

    2. The reason I don't want to go over 4V is I won't be able to charge my battery through solar cells (due to size contraints) if the voltage is >4V

    3. I'm basically trying to replicate this device, with a higher Lumen output, and larger battery capacity.
     

    Attached Files:

  9. Gryd3

    Gryd3

    4,098
    875
    Jun 25, 2014
    :D
    Those devices cheat!
    That LED will drop 3.3V across it which is why you get that reading.
    LEDs usually require a resistor to help limit the current through them. If a resistor was in place, you would most likely see a higher voltage with the switch closed.

    They take advantage of the battery having a high internal resistance... if that was a constant voltage supply, or a battery with a lower internal resistance, it would damage the LED.
     
  10. threetwothree

    threetwothree

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    Jul 23, 2015
    I thought the reason for not needing a resistor is due to having 3 in series, and therefore splitting the current into 1/3 for each LED.

    Are you saying, I'd see a higher Volatge Drop across the LED with the switch Closed if there was a resistor in the circuit? (and where in the crcuit? in series with each LED?)

    So would you describe this is an efficient desing? given they use a battery which has a higher internal resistance (therefore limitting the current flow to the LED's slightly?) and they don't have to use a resistor?

    I know I'm repeating everything but I just want to make sure I understand!

    Cheers by the way:)
     
  11. Gryd3

    Gryd3

    4,098
    875
    Jun 25, 2014
    EEP! The drawing you have shown us is 3 LEDs in 'parallel', not in series... You are right, in that the current will split 3 ways, but this is in no way a limiting factor... The only reason this design works is because the battery chosen is too weak due to it's high internal resistance to do any damage.

    In a parallel circuit, each branch will pull as much current as it needs, and the entire circuit will be sum of these values If you use 4.5V worth of batteries, and each led drops 3.3V (As it appears to be a rough number you discovered during your test) then that leaves 0.8V unused so to speak...
    Now the internal resistance of the batter can be imagined as a resistor in series with the battery. This extra 0.8V will drop across this internal resistance which will limit the current to something around what the LEDs operate at... but if this internal resistance is too small (usually from larger batteries, or simply adding more of those in parallel... even if their voltage is the same!) then more than the desired current will flow through the LEDs causing damage.
    To resolve this problem, you use an external resistor in series with EACH LED, to ensure that too much current will not flow through when provided with an expected voltage.
    There is a bit of a trick here... LEDs are not simply powered by voltage.... they are powered by current. This is usually a bit to understand, but it essentially boils down to the LED dropping a small range of voltage across itself, and the rest of the circuit compensating to keep the current in acceptable levels.
    This resource may help you to better understand : https://www.electronicspoint.com/resources/got-a-question-about-driving-leds.5/
    I encourage you to give this a read and come on back :)
    Please don't base your experiments on that dollar store keychain :(

    Because you have 3 LEDs in parallel, you would actually need to add 3 resistors; one in series with each LED.
    In a circuit, there exists resistance. As current flows across this resistance a voltage difference will form. A voltage difference will also form across LEDs and other components even as the amount of current varies. What you are measuring is actually the voltage difference of the LED, and the voltage difference caused by the resistance of the wires (which is pretty much 0) .
    The rest of the voltage is being dropped internally in the battery... by using a resistor in-line with the LED and using a larger battery, you'll find the voltage will be more stable.

    For this particular design yes.
    For any other design... no, never, not at all.
    If you wanted longer battery life, you can put another battery in parallel which will keep the voltage the same... but the internal resistance of both batteries in parallel will be lower, which will result in more current through the LEDs. This design is only ever viable as a key-chain design. Scaling it up in ANY way will require one of two things:
    - Resistor, for use in low, and medium power LED applications.
    - Constant Current Switch mode power supply for use in high power LED applications.

    Using resistors waste power due to heat, but sizing things properly can keep that to a minimum.
    Using a switch mode supply is more effecient than the resistor approach, but is more complicated unless you buy pre-made modules.

    No worries. Read away and ask away.
    Check the link I provided. Hopefully it will answer a few questions.
     
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