Energy Efficient Outdoor Lighting


0.72 Watt LED light on the left, 20 Watt halogen bulb on the right

Got your attention yet?


I dream of someday owning an off the grid home.  I'm not rich, and my debts will keep me from ever buying what I want at the time.  But I can move than direction, and slowly get to my goal.  This is one article in a series I will do on this topic.  Some of the projects are inexpensive, and this one certainly fits that bill.


Update:  I discovered after a few months of use that the LEDs were burning out.  Same thing was happening in my un-modified flashlights.  I then purchased white LEDs from Digikey, for $3.52 each.  These were the highest quality LEDs I could find.  I was careful not to exceed the 20 mA rating, and tried a few different mounting methods to mitigate heat buildup.  The results were the same.  In a matter of months, they slowly would burn out.

These LEDs are rated in the tens of thousands of hours.  But at 6 hours a night, they all died in a matter of months.  The power source was my battery bank, so very clean and stable power.

My next option was to buy a commercially available product, rather than build my own.  But after more research, feedback from buyers shows that those products faired no better.  One such review is here.  I'm beginning to believe all of the white LEDs are imported from China, based on ads from Chinese company's promoting their replacement LED products.

This probably also explains why replacement LED lights with MR16 bases aren't available at Walmart, Home Depot, Lowes, etc.

This was a fun project, and if I find a more reliable white LED, I'll revive the project.  But for now, I hooked my transformer back to the grid, and slapped 20 Watt halogen bulbs in each of my garden lights.  Sigh....  :-(

I might try one with a single 3 Watt Luxeon LED.  Far more power than what I had built, but also much less power than the halogen equivalent.  Stay tuned, I'm not done yet!



Using a Kill-A-Watt meter, I can quickly check how much power any 120 VAC appliance draws.  My outdoor lighting, which consists of 8 lights, consumes 166 Watts, or 1.45 Amps @ 120 VAC.  It basically has been running from dusk to dawn.

Harbor Freight had their 9 LED flashlight on sale for $3.99.  I bought a bag full of them.  They use 3 AAA batteries.  Keep one in my vehicle, in the house, and on the patio for when I'm walking the dog at night.

I unscrewed the head of the flashlight, attached a couple of wires, then taped it to the diffuser on the garden light.  Hey, this works!

3 AAA batteries is 4.5 Volts.  Take 3 flashlight heads, wire them in series, connect to 12 Volts, means 4 Volts per light.  All is well.  Maybe not.  Three lights are pulling 681 mA @ 12 VDC.  No load resistor in the circuit.  No problem?...

Wrong!  Big problem.  There's a reason load resistors are used.  This prevents a thermal run away from occurring.  One LED draws a little too much current, it shorts out, causing the next one to go, and so on.  Note the fried LED on the right.

The problem is all the LEDs in the flashlight are in parallel.  This is a poor way to hookup LEDs, but it is cost effective.  With only 3 AAA batteries, it's self current limiting.  When I connected 3 in series to a 12 V battery, the potential for damage greatly increased, as demonstrated by the photo to the left. 

To start the process of making the LED circuit more efficient, and safer, take the head of the flashlight apart.  The reflective collar can be slipped off.

I used a solder extractor to remove the LEDs from the circuit board.

All the components now separated.  A few of the LEDs had to be replaced as I fried them in my first experiment.

Instead of having 9 LEDs in parallel, I now have 3 in series with a load resistor.  The value of the resistor will vary with the model of LED used.  I used an Ammeter to determine the correct value.  Ideally, you should have about 20 mA running through this circuit with most LEDs.  You can run a higher current, but it will greatly reduce the life of the LED.

In this case, a 150 Ohm resistor drops the 3 LED string to just under 20 mA.

I put 3 circuits of 3 LEDs with load resistors in parallel.  I found it easier to wire the strings in a vice, then transfer them to the reflective collar.  Once the LEDs were inserted, I added a drop of superglue to each LED.


The three strings of LEDs were tied together in parallel, and connected to a 12 Volt battery.

Instead of each LED flashlight head drawing 266 mA, they now draw about 60 mA, and the current limiting resistors will keep them safe.

This gives you an idea of how each garden light was put together.  I ended up using hot glue to attach the modified flashlight head to the bottom of the glass diffuser.


So instead of drawing 166 Watts per hour, the 8 lights will now draw 5.76 Watts per hour.  Power (P) = I (Current) x E (Voltage).  P = (8 lights x 60 mA) x 12 Volts, or 5.76 Watts.  This can easily be provided by a small solar panel, which is what I'm working on.  The first of many items off the grid!




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Last updated 8/24/08    All rights reserved.