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Thread: desk lamp conversion questions

  1. #1

    Default desk lamp conversion questions

    Hello all,
    First I would like to say I am new here. I have recently purchased an old work lamp that I plan to refinish. It is currently set up as a fluorescent lamp but long story short I can not find any of those parts to fix it. So I decided I want to make the switch to LED lights. I have been looking around and have come up with a basic understanding on how to do this but I want to bounce it off some people with experience first.

    First some general info on the lamp. I would like to reuse the power cord as it is in great shape. The lamp shade is about 12-14" long, 4-5" wide and 3" deep and is of metal construction.

    Second heres my general thought I will run the existing power cord into the lamp then connect that to a 120v to 12v step down transformer (located in the lamp shade area) then to a switch of some sort(I was thinking a simple toggle) then run that to two stripes of led lights wired in series. here are links to the products I was looking at using.


    http://www.hottubworks.com/part-1-TF...p=1-TF-120V12V
    http://www.elementalled.com/high-den...rip-light.html

    please tell what you think I could post pictures of the lamp if needed.

  2. #2
    Flashaholic* JamisonM's Avatar
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    Default Re: desk lamp conversion questions

    If you don't mind me asking, what kind of work lamp is this? Do you mind posting pictures?
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  3. #3

    Default Re: desk lamp conversion questions

    ok i must be a complete idiot when it comes to posting pics but I didnt understand the instructions. so i hope this link will work.

    https://picasaweb.google.com/107915347672438124095

    please let me know if it worked. I took four pictures of the lamp. the first two are of the housing, the second two are of the white insert i had to take out that use to hold the fluorescent bulbs. I would really like to reuse most of the stuff but if it would be better to get another cord where should I start.

  4. #4
    Flashaholic* AnAppleSnail's Avatar
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    Default Re: desk lamp conversion questions

    I think the parts you have might work, but in my desk-lamp conversion I used an existing wall-wart plug. Note: You should use a fuse on the high-voltage part! Nobody wants to start a fire on their desk when they move their lamp. I crimped the ends of my plug to the prongs of a 5VDC cell phone power supply hidden in the base, running an LM317 CC driver. Your application will be similar, with the 12v transformer instead. Those are meant to go in plastic project enclosures, so be careful not to ground it by accident.

    Anytime you build something working on line voltage, check the local laws about fire liability. It'd be a bummer to have a lot of paperwork after a tragedy.
    My biggest light-hog is my camera.

  5. #5
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    Default Re: desk lamp conversion questions

    THe power supply the OP listed is just a stepdown transformer, it puts out 12v AC the strips need DC voltage. Also a transformer like that isn't doesn't have a stable voltage output, IE under no to light load it might put out more than 12volts. I would go with a meanwell type constant voltage power supply. If you are still want to use those premade led strips then I would pack as many as I could fit in the lamp you have. I would advise to always put the on/off switch on the Mains "120VAC" side of the circuit.

  6. #6

    Default Re: desk lamp conversion questions

    so it sounds like i should look at a different set up then. With wall warts or laptop power supply units how do I determine the correct match for the led strips? I will be using this lamp as a work light for my work bench and some bright light would be great. I have a limited knowledge in this area so some pointers wouldn't hurt.

  7. #7
    Flashaholic* AnAppleSnail's Avatar
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    Default Re: desk lamp conversion questions

    Get a "12v DC" power supply. You'll want a decent power rating; most LED strips are about 3 or 4 watts per meter of strip (And about 80 lumens per watt). If I arrange 6 15-cm strips of the stuff I have, I'll have a block of LED about 5cmx15cm that wants about 4W of power (250 mA at 12V). Most DC power supplies have adequate self-damping if you aren't running your LED strips too hard. The voltage may creep over time, so look for a 300 mA 12V supply (Or get more LED strips, more brightness, and more power). Consider heat on your power supply. I have a 1A 12V supply that I would not enclose, as it gets warm exposed to room air.
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  8. #8
    Flashaholic* JamisonM's Avatar
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    Default Re: desk lamp conversion questions

    jakesG23, how bright do you want to make this desk lamp? How much are you willing to put into it? What's the maximum you'd like to spend?
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  9. #9

    Default Re: desk lamp conversion questions

    Hi!

    Your project looks similar to mine:

    http://www.candlepowerforums.com/vb/...ome-brightness


    For your lamp, get an aluminium sheet to cover the open side.
    Also get a cheap 12V/5A laptop power supply from ebay.
    Buy both "white" and "warm white" high density led strips from this vendor:

    http://www.ebay.de/itm/190648195210?...84.m1439.l2649

    Stick them to your aluminium sheet, using one warm white strip for every 2 whites, like I did.
    Connect all in parallel to the 12V power supply.

    Enjoy!

    Cheers,

    Julian
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  10. #10
    Flashaholic* JamisonM's Avatar
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    Default Re: desk lamp conversion questions

    It seems a post has gone missing. jakesG23, that power supply should work, but driving the LED strip you linked above with 150mA won't produce much light. Those LED strips are rated at 12v and 242mA. According to that site, a foot of neutral white will put out 156lm and will cost you $16. A single R5 XP-G will just about equal that at half the price. Would four in a series produce enough light for you? You can also use cheaper LEDs from that site and expect them to be putting out around 400lm.

    Check out your local thrift stores and see if you can't find a higher rated 12v power supply. Try to find one rated for 350mA-500mA. I think the hardest and most expensive part of this conversion will be figuring out how to keep the LEDs cool. I'm thinking a piece of plate aluminum cut to fit snugly. You could take a couple of short wooden blocks on each side and drill some holes in the side of the lamp and aluminum plate. This would keep the plate in place and fixed to the lamp.

    As for wiring, you can use your current power cord. Take a switch and mount it in the lamp, cutting a hole if you have to. Mount it wherever it feels most comfortable. Cut your main power cord and depending on the switch, you'll have to solder or screw the wires to it. From there, you can take a short length cut from your current power cord and solder it to the power supply prongs. Female plugs for the end of power cords that have been damaged can also be purchased so you can plug the power supply in.
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  11. #11

    Default Re: desk lamp conversion questions

    Just a suggestion, but skip the premade LED strips, and start from fresh. Cut some alumium C-channel or 2.5" bar to size, and mount some XP-G's, Rebel ES's etc. to that instead. Mount the C-channel or aluminum bar inside the light, and run the lamp cord to a dedicated driver. Unless you plan on bouncing the LED's off the inside of the light use more LED's at 350mA to give you a more distributed light source -vs higher powered ones. Or, cut a sheet of acrylic diffuser and fold it inside the light. Bare LED's in the 100+ lumen range can be obnoxious to work under unless diffused.

    I've nothing against using LED strips that run off 12volt, but most of them are junk, are low powered, have nasty color, or all of the above. If you can get good strips using Osram's, Crees etc., and they aren't too pricey then go for it. Otherwise, good luck finding decent budget strips with unknown LED's. Not something you'll like working under for very long.

  12. #12

    Default Re: desk lamp conversion questions

    Well, I always use the cheapest LED strips I can find, and never had problems. I run some of them as a test continiusly since the beginning of this year, and see no degradation yet when compared to unused samples. This translates to several years worth of normal use, i.e. a couple of hours a day.
    The color can be nicely tuned by mixing cold and warm white strips at a rate preferred by the user, I like 1 warm for 2 cold ones for example.
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  13. #13

    Default Re: desk lamp conversion questions

    The reason you're having to mix colors is the color is so bad with generic Chinese LEDs in the first place. Personally it seems like less hassle to use neutrals, but as I said, good luck finding a true 'neutral' LED in a generic light strip. Good luck.

  14. #14

    Default Re: desk lamp conversion questions

    "Bad" is a rather subjective description. A cool tint is not neccessarily bad, and neither is a warm one.
    It is just that I find both not quite perfect for a desk lamp. For a living room, the warm ones would work very well. They also work very well for the lantern I built:
    http://www.candlepowerforums.com/vb/...=1#post3827793

    For a desk lamp, neutral would be a little too warm for me, so the 2:1 mix turns out to be quite perfect.
    With just cool and warm strips, one can achieve any tint one likes, without having to buy new LEDs for every variation one wants to try. Additionally, one has no hassle with heatsinking.
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  15. #15

    Default Re: desk lamp conversion questions

    sorry for dropping off the edge of the world for a bit but I had alot going on lately. I haven't had time to look for old power supplies yet but I will take a look around. As for how much i am willing to spend well I was thinking around $30-40. After reading all those posts I think my revised plan is to use a laptop supply wired into a toggle switch thats mounted on the lamp housing. then I will reuse the sheet metal surround/reflector surface to mount the leds to. Now as for the leds I am completely lost whats a XP-G? well I guess i'll google that.

    Ok googling done. Yeah I think with my skill level it would best to use a premade strip. is there a better brand then what I previously posted?
    Last edited by jakesG23; 07-24-2012 at 10:22 AM.

  16. #16

    Default Re: desk lamp conversion questions

    Yes, a 12V laptop power supply and LED strips are great for starting, it would be hard to do anything wrong.

    For the strips, please check the ebay link I posted above. These are the cheapest strips I could find, and they perform really great.
    In fact, I have never had any problems with any strips I bought.
    This message was morsed into the open end of a fiber-optic cable with a flashlight.

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