Best LED for the job

Discussion in 'General Electronics Chat' started by André Ferrato, May 27, 2015.

  1. André Ferrato

    Thread Starter Member

    Apr 5, 2015
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    Hello guys, I 'm going on my winter vacation and i intend to make a desk lamp to my girlfriend , it's an exercise to improve my skills in electronics and learn more about the incredible lights of our simple world. Then I mounted a circuit in which she will be able to control the intensity of light through PWM , and also have an intensity indicator ( bargraph ) . I came here to ask the gentlemen who certainly have more experience than me in this matter, the idea is to use LEDs to achieve this, but when I go to pick one, I get very confused by the available data, such as the angle of each LED , or those lumens ( mcd ).

    - What is the best pick for this job ? I mean CFL or LED ? I thought about LED, because they're small and cheap.

    I believe i was not clear in my explanation, but what i am trying to ask or start talking about, is what difficulties lie ahead to me, like... i never tried to make a light source, so i don't know about how large the spot will be by using this or that.. got what i meant ? Like, a 21000mcd seens to be a violent value, but maybe for me that never worked with this. Or the lens job at this project.

    That feeling of not being clear enough. :(
     
  2. Sensacell

    Well-Known Member

    Jun 19, 2012
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    Use an LED.
    The hardest part of your project will be the thermal management of the LED.
    You must mount the LED on a substantial heat sink.
     
  3. cornishlad

    Member

    Jul 31, 2013
    196
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    After the QI bulb holder burnt up in my desk lamp I bought oneof these : http://www.ebay.co.uk/itm/48-LED-12...418?pt=LH_DefaultDomain_3&hash=item35c2351cfa. to replace the QIbulb (12 volt DC)
    They give about the right of light (for me anyway) and are simple to install. PWM modules are also listed on eBay but can't think why you would want a dimmer. The bargraph will be the most complicated part of the scheme.
    sensacell posted while I wrote !
     
  4. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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  5. wayneh

    Expert

    Sep 9, 2010
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    One additional thing to consider is optics. Desk lamps typically use parabolic reflectors to direct most of the light downward, and position the lighting element so that stray light is shaded. In other words, you need to consider the angle of the beam. That 21000mcd LED you mentioned is almost certainly in a plastic package with a lens to greatly narrow the beam, raising the mcd value. In a desk lamp it might produce just a 4" diameter bright spot on your work surface.
     
  6. André Ferrato

    Thread Starter Member

    Apr 5, 2015
    206
    1
    Sorry for the delay to answer. The mechanical aspect of the lamp will be like this one i think, at least that is the model i am using:
    993180465_181460.jpg

    As you may see, it's a very simple desk lamp, this model uses a CFL. My project uses basically a PWM for the LED intensity, also using a LED DRIVER IC and a bargraph with the BARGRAPH DRIVER IC( Simple voltage divider with op-amps, not so simple actually) for the indicator of the intensity. As wayneh stated, i worry about the diameter of the light spot on the desk, because like you said the LED already has it's lens. So how could we go around this ? Is the 48 automotive LED that cornishlad showed a solution ? My main concern is this actually, how to make the light spot large enough and how to make the light not so bright.

    The following leds doesn't have directing lens right ? Mcgyvr sent that.
    http://www.ebay.com/itm/1pcs-3W-5W-...t=LH_DefaultDomain_0&var=&hash=item51c691dc8b
     
  7. cornishlad

    Member

    Jul 31, 2013
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    The ones I linked to are so cheap why not buy one and see if it suits. They give a very widespread light, need no cooling or lenses. I have been using mine at my computer desk for a year and am quite happy with it. The actual one I got was warm white but the link I gave just says "white". LED white can be a bit too bluey for some.
     
  8. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    The one I linked to probably has a 120 deg viewing angle.. Which IMO is probably just fine for a desk lamp.. no lens needed.
    In general, LED lenses will "decrease" the LEDs normal viewing angle for applications where you may need more light to penetrate further.

    Beware staring directly into LED lights CAN cause eye damage.. I'd actually recommend a diffuser.
     
  9. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Sorry to ask something obvious but doesn't the lamp itself "display" it's own intensity?

    Why a bargraph full of redundant information?

    Why would I look at the graph when I'm just going to see how much light the lamp is giving off?
     
  10. André Ferrato

    Thread Starter Member

    Apr 5, 2015
    206
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    Oh the bargraph is just to make it fancy, it's for my girl and she liked the idea. A diffuser ?
     
  11. wayneh

    Expert

    Sep 9, 2010
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    Look into the LM3914 for your bargraph.
     
  12. André Ferrato

    Thread Starter Member

    Apr 5, 2015
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    Yes, this is the one i am going to use and i didn't knew that LED could be harmful if looked directly. Anyway, i'll try these options you all gave me, but there is a problem that came to me yesterday... I thought about making it in a way that both a battery and the power supply from the house could be used, so a 110 AC and if she wanted to move around, a battery... is this hard to achieve ? I thought of some ways, none of them was simple.
     
  13. wayneh

    Expert

    Sep 9, 2010
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    No battery you want to carry around is going to have enough juice to run the desk lamp. 4 D cells or the equivalent of a laptop's battery pack might give a practical amount of power, but that takes room and adds weight.

    I suppose you could have a "low power" mode that uses less LEDs when running on a battery.
     
  14. André Ferrato

    Thread Starter Member

    Apr 5, 2015
    206
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    Yeah i was thinking about the discharge issue.. i would need a very large battery to make it good.. forget about that, i will just use the plugged mode rsrs
     
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