LED Value!!!!

Discussion in 'General Electronics Chat' started by redlight000, Apr 2, 2010.

  1. redlight000

    Thread Starter Member

    Feb 26, 2010
    66
    2

    Hi all,
    I've got a Superbright LED, and I do mean bright.. now Im not new to series resistors to leds... but a tad unsure of this one, I rang the supplier of the LED.. ok and "What I thought of the answer was not right well not in my eyes.. a complete idiot who ever worked in the Technical dept of the Store in question...

    I want to put 9Volts into the led with the series resistor, otherwise the battery will kill the LED as "you all know that" Now what I've worked out from the specs of the LED in question.. & worked out that between 100-400 ohms would be ok...

    Here's the Specs of the LED

    Power dissipation 130mw
    Peak forward current = 100ma
    Continuous forward current :50ma
    Derating factor: 0.4ma
    Reverse voltage 5V
    ======================================================

    forward voltage min 2.3v Max 2.6v
    Luminous Intensity lv min 2500 max 7200mcd
    Dominant Wavelength 625nm
    Spectrum Radiation Bandwidth 20nm
    Reverse current lr 10ua
    Viewing angle 30degrees
    -----------------------------------------------------------------------

    So thats the Specs, in case you asked...
    So am I right with my resisitor Value..
    thanks for reading this.. !!

    PS: The Tech bloke!! said 470K :rolleyes:
    cheers all
     
  2. Jony130

    AAC Fanatic!

    Feb 17, 2009
    3,957
    1,097
    Hmm, Ohms law
    R=U/I = (9V- 2.6V) / 10mA...30mA =
    So we pick from 220Ω to 680Ω.
    I would chose 680Ω
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Well, the most relevant points are the Vf (forward voltage) min of 2.3v and max of 2.6v, and the specified max continuous current of 50mA.

    Realize that 9v batteries are pretty wimpy. If you run the LED at full power, the battery won't last very long.

    Anyway, the generalized formula for LED current limiting resistors is:
    Rlimit >= (Vsupply - VfLED)/DesiredCurrent
    So, let's err on the safe side and assume your LED's Vf is 2.3 @50mA.
    Rlimit >= (9v-2.3v)/50mA
    Rlimit >= 6.7/0.05
    Rlimit >= 134 Ohms.
    The closest standard resistance value >= 134 Ohms is 150 Ohms.
    Table: http://www.logwell.com/tech/components/resistor_values.html
    (bookmark that page, use the green E24 columns)
    Now if you don't mind using combinations of resistors in series or parallel to get closer to the resistance you need, here's a calculator:
    http://www.qsl.net/in3otd/parallr.html
     
  4. Bychon

    Member

    Mar 12, 2010
    469
    41
    Wookie got the math right.
     
  5. cjdelphi

    New Member

    Mar 26, 2009
    272
    2
    What LED is it? is it a Nicha? 5mm?

    BTW, 100ma is not very strong these days for an LED :p (Cree's XPG R5 can handle 1amp@3.6v and give off more or less the intensity of a 60watt incan bulb with good heatsinking)
     
  6. redlight000

    Thread Starter Member

    Feb 26, 2010
    66
    2
    Hi all,

    firstly thanks for a great answers to this, an sgt.wookie... spot on maths well done by saying that I mean I did do all that but my input to the calculator must of got a bit wrong.. I was a bit out..!!!

    Yes with sgt.wookie and the rest of you its really good to know that you do all know what your talking about, I knew 470k was stupid..!!! and thats a engineer from a well know store in Essex!!!

    much thanks to you all
    regards
    redlight000
    :D
     
  7. redlight000

    Thread Starter Member

    Feb 26, 2010
    66
    2
    Hi Bychon,

    No the LED is made by Agilight.. god knows who they are, Yes I know there's Brighter LED's out there... like the one you mentioned, but I done a test on a 100 ohm Resistor, and stupid as I was I was peering into the LED ie looking at the Brightness.. and that was for about 5seconds... and after I switched the power off, I saw all red dots and my brain if this makes sence, went all disorentated.. any long that 5secsonds, and it would make one ill, I mean a bit like a Strobe... which if set right is in sync with your brain wave Frequecny..!!! horrible I HAVE NOT done that again..

    nuff said thanks all.
    redlight000
     
  8. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    I've said this many times on the board, but it needs to be repeated.

    The old style LEDs you used to get 20 years ago were low current (10mA-15mA), low intensity, and diffused. These were quite safe for use as indicators.

    The new super-bright LEDs can cause permanent loss of vision if you stare at them. The damage starts to occur in just seconds. The light is intense, but it's a "cold" light, so you don't feel the damage occurring. Cheap LEDs from auction sites are focused very narrowly, so the light is concentrated in a very narrow viewing angle.

    If I'm working with super-bright LEDs, I'll use a sheet of white paper between my eyes and the LEDs to diffuse the light. Other light diffusers that work well are the white plastic containers that dairy items are packaged in, like sour cream and cottage cheese.

    You only get one pair of eyes. Protect them.
     
    redlight000 likes this.
  9. redlight000

    Thread Starter Member

    Feb 26, 2010
    66
    2
    Hi there,

    cheers for the reply, Just wondering where do you obtain those LEDs then Please, Just asking..
    thanks
    :D
     
  10. redlight000

    Thread Starter Member

    Feb 26, 2010
    66
    2
    Hi SGt.

    Yes thanks for that, I began to feel really weird.. with this bright red Led, Ive worked with the White.. Led's and I did not feel ill!!! but your absoloutly right on this flipping dangerous... imagine 4 of those in a line, protruding out of your project box... and have a push button to momnentaraly power on.. I would hate to think what effect that would cause.. sgtwookie.. do you agree? & also slightly changing the subject.. Ive read.. or seen on a write up on specific frequencies.. that Just 20hz signal can be dangerous.. can you throw a bit of info on that please ? reason asking "How can 20hz be dangerous"????

    many thanks and I will use that paper.. for sure.. to be honest Ive not gone near it since!!! :-(
    cheers
    redlight000
     
  11. bertus

    Administrator

    Apr 5, 2008
    15,638
    2,344
    Hello,

    There are some people who get epileptic reaction on the 20 Hz light.
    The 20 Hz will trigger this epileptic reactions.

    Bertus
     
  12. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Actually, I have quite a collection that I've acquired over the last 30 years or so. I have purchased some of the cheap LEDs from auction sites just for experimenting with.

    I'm in the States, so my suppliers are different from those you use.

    Farnell UK, RS Components and Maplin are some popular UK sites I've heard about. Farnell UK's counterpart in the States is Newark.

    You really need to read the manufacturer's datasheet for the LEDs to determine what you are buying. Wide-angle LEDs with diffused lenses are much less likely to cause harm than those that are narrowly focused.

    You can also operate these newer super-bright LEDs on reduced current to produce a good bit less light.

    I have been known to re-focus the lenses of some really narrow LEDs using a cloth polishing wheel mounted on a grinder and a bit of emery or rouge. The difficult part is to keep them from vanishing under the workbench at high speed if the wheel catches them. :eek:
     
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  13. SgtWookie

    Expert

    Jul 17, 2007
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    Like Bertus said, some people have a bad reaction when light is flashed at a low frequency. The frequency varies depending on the individual. Most people aren't bothered very much by this effect.
     
    redlight000 likes this.
  14. retched

    AAC Fanatic!

    Dec 5, 2009
    5,201
    312
    If you felt nauseous, you may be interested in a "less-than-lethal" product that is in production. It is called the "Dazzler". It is a group of LEDs that flash in a pattern and rate than induces dizziness and nausea even confusion in the people subjected to its output.
     
  15. iulian28ti

    Member

    Dec 4, 2009
    42
    0
    What exactly is the Vmax ? The max read voltage at maximum current and temperature ?
     
  16. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    That is the maximum Vf at the specified current. You usually do not want to use that when calculating a current limiting resistor, because if the Vf of your LED in question is on the low end, it will receive too much current.
     
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  17. redlight000

    Thread Starter Member

    Feb 26, 2010
    66
    2
    Hi Reched,
    hmmm "YES" I've come across the dazzler... I watched a video link, on it.. and the person pointed it to the Volenteer.. <maybe spelt wrong) and the guy.. sort of swerved to one side.. Back to this horrid LED as put in my first post.. no I did not feel sick.. but saw loads of red dots...its called after image (I think), and could not hardly see my Breadboard that I do my Prototype work on..!!! Im really not kidding here..

    And Felt really disorentated for a good part of the Next day :-( stupid as I was to peer in the thing but.. I did not realise the outcome.. huh I do now ... wont stare at that led ever like that again.. and it was not even Flashing of which I normally do with a basic astable osc) < dont go over 11hz cos the eye dont see it as flashing because its to quick for the eye to register... Phew..

    Im defo not into hurting peeps eyes but if I was to make this up (a circuit for of them in a straight line..and use a push button to activate it for a about say 10seconds I dread to think what/ how the person would react.. horrible... get one.. and try BUT dont stare into it... there not state of the art Led's but very good brightness for £1.69!!!! thats each!!!

    If you want the source of how to get them & the code of the Item ..email.. Im not putting it here..incase newbie electronics peeps, use them wrongly..

    cheers all
    and for the safety factor...
    oh dear what have I done again.. normally I deafen myself with sound.. but my ears are imune now well I think so :-;
    once again really good answers and help from you all.
    thx
    redlight000
    :D
     
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