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New Project: Little Big Lamp

Build a bright, energy-efficient lamp with LEDs and PVC.

New Project: Little Big Lamp

The most popular item I ever built for MAKE just happened to be the simplest: an LED desk lamp. This was in Volume 08, in 2006, when white LEDs were a hot new product. The most powerful ones I could find were 1cm in diameter, rated to deliver 100,000mcd (millicandle). The light wasn’t exactly white — it had a freaky purplish hue. But I liked the weird color, because it showed we were early adopters of cutting-edge illumination!

Recently I started wondering if I could downsize and upgrade the original lamp. So I took a fresh look at those traditional, through-hole, single-component LED “indicators” (as they are properly known).

The 5mm ones are now a lot more powerful than the 1cm type I used in the past. Some of them, known as “5-chip,” have 5 light-emitting elements squeezed into one 5mm package, sucking down 100mA of forward current at around 3.3V DC.

They’re still rated at 100,000mcd, but 6 years ago, the ones I used were rated for only 20° of beam spread. Today’s 5-chip LEDs claim a spread of 60°. Does that mean they’re 3 times as bright? No, they should be 9 times as bright, because the light is delivered over a two-dimensional area!

Since I used 72 of the big old ones, and the new ones should be 9 times as bright, I would only need 8 to get the same illumination. But why not go for greater output?

Here we’ll use the traditional-style 5mm LEDs. RadioShack, for instance, offers them as part #276-017. Since they use exactly the same 3.3V DC as the 5-chip variety, you can substitute either in this project without changing the circuit.

Fabrication Choices

I opted for a 12V DC power supply, to make the lamp function in motor homes, where LEDs are ideal to conserve power. For use with 115V AC, you need an adapter that delivers 12V DC at 1 amp. Here we’ll use RadioShack part #273-358.

Instead of adding a series resistor with each LED, the most efficient way to power them from 12V DC is by series-wiring them in threes. This means you need 10V DC for each set. How to get 10V from 12V power? Pulse-width modulation is the way to go. You send a stream of pulses, too rapid for the eye to see, and vary the gaps between them to limit the average current. If you add a potentiometer, this can act as a dimmer. Only a few electronic parts are needed, and they’re listed in the materials and specified in Step 5.

Note that if you use old-style low-power LEDs, your AC adapter can be down-rated to 300mA, which should cost less.

How to build the actual lamp? I decided to use PVC plumbing supplies. For the additional pieces that would hold everything together, I chose 1/8″ white ABS plastic, but you can use plywood if you prefer.

Charles Platt

Charles Platt

Charles Platt is the author of Make: Electronics, an introductory guide for all ages. He is completing a sequel, Make: More Electronics, and is the author of Volume One of the Encyclopedia of Electronic Components. Volumes Two and Three are in preparation. makershed.com/platt


18 Responses to New Project: Little Big Lamp

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  1. Goli Mohammadi on said:

    Hi sandrorahn,

    The equivalent is the ULN2003 Darlington array. Can you find that one in Brazil?

    • hello, I construct the circuit in the breadboard using the ULN2003 darlignton array as a substitute to NTE2013 but it didn’t work. is there any changes to the circuit? please help. thaks

  2. I would use an old computer battery, or camcorder battery, and charge it with a wall wart trickle charger. Or from a cig,ligher plug but watch the current. The weight of the battery would stabilize the lamp base

  3. Ian Caister on said:

    In short: the darlingtons allow the control circuit to switch much higher currents than it would be able to without them.

    The darlington array effectively operates as a digital switch.

    This design uses a technique called ‘PWM’ or pulse width modulation. Effectively the 555 produces an output that is switching on and off faster than you can see. By varying the potentiometer you change the relative amount of time the output is ‘on’ for and hence adjust the apparent brightness of the LEDs.

    The issue is the 555 can only sink a few miliamps of current, much less than what is needed to drive all those LEDs, so instead the 555 drives the darlingtons which take very little current to operate but can sink many times more than the 555. The darlington is basically like a relay.

  4. billy builder on said:

    Why are all the links for radioshack? The prices there are like literally 10 times ordering from any other online electronics distributor. Why not jameco or mauser? $2.50 for 2 LEDs? Good grief.

  5. instead of a potentiometer, can the circuit accept PWM from arduino to dim the lamp. if so how can i configure the circuit? thanks

  6. Camilo on said:

    maybe i’m blind but i can’t find the template to make the holes

  7. pravin vairar on said:

    Is any substitution possible for NTE2013 Darlington array?

  8. You can you a Brace or a large hand crank drill to use the hole saw safely with much less expense than a drill press. Properly set up hand powered tools can be very efficient and cost effective to their tialed brethern. Hand tools are very modern they are all cordless. ;) Like all trades it helps to have a good mentor. Sawmill CreeK and Wood Central are good peopl to help you on the hand tool path.

  9. czy można polaczyc 2 NTE2013 by zasilić 36/3 diod

  10. You can connect 2 NTE 2013 to power 36/3 LEDs

  11. Mark Twain on said:

    wow what a waste of time. just make an incandescent or florescent lamp dude in a fifth the time.

  12. Is there anything to watch out for with European power supplies?

  13. Well I finally got it to work with three bulbs just like you did , but the volts keep fluctuating and the bulbs won’t stay lit, did I miss something ??? Oh by the way great project ,,,

  14. Hey guys you never answered my question ,,,

  15. Hello, thanks for this guide – this is my first project involving electronics.

    I’ve got it all set up in the breadboard, everything worked fine until I got to the last bit. everything is hooked up but when i turn the potentiometer it dims and brightens the light, but 1) it gets brighter as i turn it to the left, which is counter-intuitive and 2) when i turn it all the way to the dimmest, i was expecting it to be the “off” position, but instead it is just dim – is that how it was supposed to be or did I do something wrong.

    the only thing i did different was that I wired it all to one light instead of leaving six seperate neutral wires for the leds, as I don’t have any intention of controlling the sets of three seperatly.

    thanks!

  16. Pingback: Hacedores – Haz una lámpara de escritorio con LEDs y PVC

  17. Pingback: Creative Lamp Project | University School Digital Fabrication

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