LED Lighting System Project

Discussion in 'General Electronics Chat' started by Exodus00FF, Mar 19, 2009.

  1. Exodus00FF

    Thread Starter New Member

    Mar 19, 2009
    9
    0
    Hello Everyone, I'm a first time poster here. I've been googling in regards to creating an Aquarium Controller. Most of the time I often found myself being directed here for answers to my conundrums.

    What I am looking to do is to create a Series of large LED Arrays to light my aquarium. To do this I'm going to use quite a few .5 Watt Leds (Probably about 100 or so), and modify the light from those white LEDs (B/C they're not really that white and have more of a blue tint to them), with Red and Green LEDs, possibly Amber as well.

    To control these I've purchased an Arduino Microcontroller.

    But I still have questions about LEDs that I am hoping can be answered here.

    But before I ask I'd like to give a little background about myself. I am a Computer Programmer by trade, and I find Electricity & circuits to be intriguing. I only have a base level of knowledge about circuits & Electricity, but I would like to learn more.

    Now... Question Time!

    I've noticed that often when I see schematics of LEDs they often have Resistors attached to the front of them. But my understanding of Diodes is very basic and I do not understand why. As far as I know, Diodes are basically one way streets, except when you apply to much voltage to the wrong end in which it becomes reversed biased.

    • Why is there a need for resistors?

    Also what can anyone tell me about LED Drivers. The term seems to vary from place to place, but from what I've pieced together an LED Driver is basically a power source for the LEDS. Some are constant current and others are not.

    • Is my assumption of LED Drivers correct?

    • What seperates a Constant Current LED Driver from a non-Constant Current LED Driver?

    • If you use a Constant Current LED Driver, do you still need resistors?

    Now I am assuming that a Constant Current LED Driver is prefered over a regular one. Can anyone recommend an LED Driver IC that I can supply power via a regulated power supply, and also has the ability to Pulse Width Modulate 4 or 5 different channels?
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,647
    2,346
    Hello,

    The resistors used in series with the leds are for current limiting.

    Most LED drivers are constant current sources, some even with boost converters,
    so more leds can be placed in series using a lower input voltage.

    Like I said most are constant current, non-constant current are "normal" power supplies,
    so you will need resistors to limit the current.

    No, Take care the current is fitting the used leds.


    Here is more information on leds and circuits with leds.
    http://www.educypedia.be/electronics/composemiconductorsled.htm
    http://www.educypedia.be/electronics/circuitsled.htm

    Greetings,
    Bertus
     
  3. flat5

    Active Member

    Nov 13, 2008
    403
    17
    Do the fish care how bright their environment is?
    Are they stressed if it is too bright?
     
  4. markosillypig

    Active Member

    Jul 21, 2008
    184
    0
  5. Exodus00FF

    Thread Starter New Member

    Mar 19, 2009
    9
    0
    To answer your question, yes some fish do care, others don't. Depends on your fish. Clown Loaches for example do not like bright light. Gouramis don't really care.

    The objective of what I am attempting to do with the microcontroller is adjust the lighting of my white LEDS with Green Amber and Red, which I can adjust to create Dawn, Daylight (5500k I believe), Afternoon Light (6700K), Dusk, and finally moonlighting.

    Which of course is the reason why I need an appriopriate LED Driver :)
     
  6. Exodus00FF

    Thread Starter New Member

    Mar 19, 2009
    9
    0

    So Bertus, you said that they are current limiting which I'm assuming by current you actually mean current (Amps.) How can I determine the maximum safe allowable current that an LED can handle. Would it be the Peak Forward Current?


    Here are the specs that I have available for my LEDs

    Forward Voltage: (ConditionIf=20mA) Min3.2 Max3.4V
    Reverse Current:
    (ConditionVR=5V) Max10uA
    Luminous Intensity:
    (ConditionIF=20mA) 25,000mcd
    50% Power Angle:
    (ConditionIF=20mA) 140degrees

    Absolute Maximum Ratings (Ta = 25°C)
    Power Dissipation PD:
    100 mW
    Forward Current (DC):
    IF 30 mA
    Peak Forward Current:
    100 mA
    Reverse Voltage:
    5V

     
  7. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    The absolute maximum would be 30mA @ 3.3v, which translates to 100mW.
    You wouldn't want to run them at that power continuously.
    The Peak Forward Current would be for a very low duty cycle. That should be specified somewhere in the datasheet for the LED.

    Your typical Vf (Forward Voltage) would run about 3.3v @ 20mA.
     
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