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Lemon Flashlight.

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intro; Lemon Flashlight, my electro-culinary dish!

Harness the power of fruit!  I give you the Lemon flashlight . It’s the solution to the considerable worldwide energy problems that scientists have struggled with for so long. Powered by a single lemon, and with a brightness in a league of it’s own, there’s little stopping this flashlight from becoming a worldwide must have light.

Stuff you’ll need:

  • Foil
  • Small piece of cardboard
  • LED (lowest voltage LED you can find)
  • Thick copper cable. About 2 foot long
  • Block of wood 15cm by 5cm by any thickness
  • Galvanized nails about 1.5″ – 2″ long  (MUST be zinc galvanized)
  • Small panel pins/nails
  • Drawing pin (could use nails if not available)
  • Sheet of Paper
  • Small pieces of wire
  • Steel wire wool
  • 2 litre plastic drinks bottle, or thin plastic

This instructable shows how to build a 5 cell version. I later built an 11 cell version in the hope of getting more light, but it’s actually worse!. I guess the internal resistance of lemons is just too high.
Step 1;
You’ll need to strip the insulation off the copper cable so that you have nice bare copper wire.  Separate the strands of wire ready for the next step.

Heavy copper wire - to strip.

step 2 Form coils for the plates

To contact each lemon slice, you’ll need a copper coil and two galvanized nails. . I started forming the copper coils using small tweezers until they were around 3/4″ diameter then I just formed the rest using my hands. Leave around 3″ of straight copper wire to attach to the nails.

You need to make 5 coils, and when you’ve done that you can attach the end of the wire to the nails, wrap around 3 turns around the nail. You want the nails to sit around 3mm away from the copper coil when they are finished.

Form-coils-for-the-plates Form-coils-for-the-plates b Form-coils-for-the-plates c

step 3 Nail in the “plates”  – The plates are nailed to the block of wood. Nail two galvanized nails to the end of your block of wood about an inch away from the end. Using pliers, cut the heads of the nails off. This is so that you can push the slices of lemon into the plates easily.

Remove all of the nails that you twisted the copper wire around in step 2. You can now nail all of the copper springs in place. They are all nailed in line with each other about 5mm between the nails and the next copper spiral. As you nail each on down, cut the heads off the nails.


Nail-in-the-plates d

Strip about 2″ worth of insulation off a short piece of wire (any kind of insulated wire will do, about 10cm long) and wrap this around the two nails that you nailed on first.

Attach-a-wire a Attach-a-wire c

step 5 Make a switch; Take a piece of the thick wire you used to make the spirals, and form a small loop. This will be a pivot point for the switch. Form the rest of it in the shape shown in the photo’s. There are two stop points for the switch made from panel pins (thin nails). One of the stops is a nail nailed onto the side of the wood and bent upwards. The other is just  nailed straight up around an inch away. Push a pin into the pivot point

With the stop points complete, you can attached the other end of the wire that you connected in step 4. Then, push a drawing pin through the pivot point to allow it to pivot. To compete the switch, an elastic band is tied from the switch to the first nails that you nailed into the board. This returns the switch to the off position when not in use.

step 6 A reflector; I made a simple reflector to direct the huge amounts of dazzling light emitted from this device. It’s made from paper covered in foil formed in a cone shape. I drew and cut out a paper circle around 80mm diameter,  and cut the same out of  aluminium foil. Tape the two together.


Then cut a straight line to the centre, and a cut a small 1cm circle out of the centre. You can roll it around now, like one of those protective collars vets give to animals to stop them injuring themselves even more. Tape the cone together at desired shape.

The reflector is attached to the wood using a small piece of cardboard that has and angle cut at the same angle as the reflector. This is taped to the reflector and to the wood.


Reflector b Reflector b
Fit the device!!

Reflector e

step 7 Plastic insulators;  Between each cell there needs to be some little plastic separators to prevent the lemons touching each other. They are simply plastic squares cut from a drinks bottle about 50mm by 50mm.  These separators go between the copper coil and the nail that that copper coil is connected to.

step 8 Test an led; Now you can test an LED to see if it works. Slice the lemon into about  5 pieces, discard the ends. Put the slice in between the plates.

Cut two pieces of wire about two inches long, strip the ends and attach a piece to each of the LED legs. Touch one of the wires the copper coil nearest the reflector, and touch the other wire to the copper on the switch. Does it light up ? If not try it the other way. If it still doesn’t light up, there’s either something wrong with your wiring, the lemons aren’t juicy enough, or the LED is too high a voltage. The led I used lit up dimply at around 1.8V Test-an-le

If it’s working, you can twist the wires around the last copper coil, and the straight nail stop on the switch.

step 9 If it’s working!…

You can tape the LED onto the cardboard behind the reflector. It’s finished now. With any luck, yours will be considerably brighter than my version. Test different LEDs and different lemons. Try adding a joule thief, experiment..  Have fun!

And remember, world domination of the lemon torch (flashlight if you’re American) could happen at an moment! Be prepared.

Don’t forget, you can use the sliced lemon in your favourite dishes even after you’ve run them flat..

Finished product.

Finished product. - but change the lemons.

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About pfiddle

Fiddle teacher - mostly Irish trad. Fiddle, mandolin and concertina. Eco-warrior, won E.U. Green Flower Award for Eco Accommodation. Also Irish (Gold) GHA. Green Hospitality Award. Mad keen on self-build - especially straw-bale and cob. 55 with a full head of (slightly) graying hair. No tattoos or piercings. Fond of animals - but legally so. Fond of food - I eat nothing else. Vegetarian by choice, Irish by the grace of birth, Munster by force of (rugby) arms.

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