LED’ing me down the garden (lighting) path
While I had wanted to have a series of illuminated buildings on my layout for quite a while, I was partially concerned by the amount of electricity it would all take. In my general reading, though, I had found that light-emitting diodes (LEDs) have in recent years become more powerful and able to generate far more light with far less electricity than standard incandescent bulbs. Of course, it’s all relative: an LED might generate 10,000 millicandelas and have a beam angle of 15 degrees, but that would represent only about one-half a lumen; whereas, a 100-watt U.S. light bulb generates about 1500 lumens. Conversely, an LED uses only a milliwatt, so there you go.
But hey: I’m lighting tiny buildings — I only need fractions of lumens or one or two lumens anyway. And current “super bright” LED technologies actually get us up around 60,000 millicandelas (depending upon the color of the LED), which with a 15-degree beam angle gets us around 3½ lumens.
Another LED advantage is their life: they usually fizzle out at around 100,000 hours, whereas incandescent bulbs go anywhere from 1000 to 2000 hours. (For more than you ever wanted to know about using LEDs in the home, visit Terry Ridder’s essay on LED Christmas lights.)
The bad thing about LEDs is their price: you can pay $1.50 for a small, rather low effective LED at Radio Shack. Even the electronics mail-order houses such as Jameco or Mouser want 75 cents for an LED. Enter eBay.
There are probably a dozen suppliers of LEDs out of Asia who sell on eBay; I happened to pick Light of Victory LED Store of Hong Kong (http://stores.ebay.com/Light-of-Victory-Led-Store-lvehk/) early on and have now purchased five packages of 50 10mm LEDs (in different colors) over a six-month period with no problems. The LEDs themselves have been fine and most are set up as “Buy It Now” at $6 per 50; unfortunately, there’s a $11.50 shipping charge (though Victory supports combined shipping, so you can still drive the price per device down). On a one-package price with shipping, each LED costs 35 cents, or half of the cheapest domestic suppliers.
I don’t get a kick-back from Victory and they’re listed here only because I’ve found their products and service to meet my needs. You can buy your LEDs anywhere you want. If they don’t come with a resistor, I’d suggest that you know their forward-voltage and visit the web site http://led.linear1.org/1led.wiz for single implementations (like the lamp post) or http://led.linear1.org/led.wiz for multiple-LED implementations to calculate the resistors needed.
The Victory packages come with resistors so that they work in 12-volt environments (many people are using LEDs with their automobiles, which usually have 12-volt circuits). Sometimes I use these, sometimes I don’t.
Another interesting source for LEDs is Christmas lights; while many new strings of Christmas lights are still incandenscent, there are a growing number of manufacturers of LED-based Christmas lights. In the 2007 holiday season, Walgreens is selling a 15-LED, battery-operated string for $4; you even get a nice holder out of the deal and the individual bulbs end up costing around 30 cents per bulb.
LEDs typically operate at around 3 volts (red, orange, yellow and amber LEDs are usually rated at 2 volts, while the blue, green, white and warm-white LEDs work at around 3.3 volts) and though alternating current can drive an LED, using that type of electricity means that the LED is actually off half the time. Since under AC the LED is cycling at 120mHz, it’s so fast you can’t see it turn off and on, and the cycling therefore makes the LED dimmer than it would be with direct current. So, since we’re trying to squeeze as much light out of one of these as possible, we need to deliver DC to the LED from the Malibu transformer.
The resistor supplied by Victory provides the correct amount of current; now I just needed to convert it from AC to DC.
To get the current conversion, I went with a bridge rectifier; I could have linked four diodes together to achieve the same result, but why bother? While a typical Radio Shack rectifier for this type of application (Part No. 276-1152) will run you $1.50 (plus tax), they can be purchased in quantity from an electronics supplier for as little as 50 cents each. (See my thoughts on buying components.)
In one of my first experiments hooking up the LED, the resistor and the rectifier to a 12-volt, AC current, though, I found the resistor overheated, becoming too hot to handle. Since I wanted to embed the electronics in the base of the lamp post, I couldn’t have an overheated resistor. Trying again, I switched the sequence (putting the resistor before the rectifier, rather than after it) and found that this way it didn’t overheat.
Another big issue with LEDs is their angle of beam, which is usually about 15 degrees from the end of the LED lens outward. I guess a good way to think of this is that these are spotlights not floodlights. In the application of illuminating buildings and making ambient light on lamp posts, we need them to act more as flood lights.
Here we enter the realm of the refraction and reflection of light; I’m a little light (pun intended) on the physics, but I do understand that if you focus the beam of an LED against something that will refract and reflect, that beam will be easier to see than the lamp itself. For the lamp posts, I encase the LED in a plastic bottle cap that has plenty of facets inside and outside, giving the light plenty of places to refract. In the case of structure interiors, I use a plastic cylinder and paint the interior of the buildings white. The light bounces all around in both the cylinder and the building, making the light inside easy to see from a distance.
Here are some projects that I’ve developed that use LEDs for backyard railway illumination:
• Building 1:20.3-scale lamp posts
• A structure illuminated with ‘fire light’
• A structure illuminated with ‘fluorescent light’
• A circuit to flash multiple LEDs
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