nl-2011-10-spotlight

LED’s of all colors unite! photo on Wikimedia by Rabenkind

Spotlight

on LEDs

by Raymond G. Potter

More than a century ago, fast talking hucksters would often roll into town touting the latest, greatest snake oil, fit to cure what ails ya’. In the twenty-first century, it’s no snake-oil sales pitch to say that Light Emitting Diodes (LED’s) are the cure to a variety of lighting and sensory problems encountered by model railroaders.

LED’s of all colors unite! photo on Wikimedia by Rabenkind

LED’s of all colors unite! photo on Wikimedia by Rabenkin

First, what is an LED? Early technologists researching semiconductors (the material that computer chips are made from) found that under certain conditions, they could emit light, either infrared or visible. At first this was a curiosity but in the 60’s the first practical visible LED was created by Nick Holonyak Jr. at GE. It took almost a decade for the technology to become economically viable and the age of light without light-bulbs had begun. It took quite a few more years before the more useful colors like white and blue were developed, but now, we can easily duplicate any color we like with LED’s affordably. No longer just the mainstay of pocket calculators, LED’s can now be found in everything from traffic signals to tail-lights to TV screens.

What’s the big deal with LED’s? I mean we have light bulbs and they’re pretty good, right? LED’s have several advantages over the general purpose incandescent bulb, which lights by running current through a filament in near vacuum. Why are LEDs one of technology’s greatest gifts to the model-maker?

  1. LED’s use much less electricity than bulbs. This means less drain on batteries or power packs and longer life for sealed components.
  2. Less power used has a side benefit of less heat thrown away. That light bulb you’re lighting your passenger car with might be slowly deforming the plastic roof of the car. An LED will get only slightly warm, usually not enough to damage plastic components.
  3. LED’s only light in the specific color they are designed for. No excess energy is wasted filtering out other colors from white light to get the color red, for example.
  4. LED’s have a much longer life span than bulbs, on the order of thousands to tens of thousands of hours.
  5. They’re less delicate too! Dropping your precious LED equipped model (we NEVER recommend dropping any model) might bust a bulb, but your LED will be OK!
  6. LED’s set in infrared ranges, in concert with additional circuitry, can be used to detect the presence of nearby objects to trigger animation or signaling events (ironically, the signals are usually also LED’s).
  7. LED’s low power demands make them ideal for working directly with logic circuits to respond to events. This means chase lights, blinkies for radio towers, etc. They also look great on control panels.
  8. Today’s LED’s are considerably brighter than those of years ago. Single white LED’s, when lit up, are so bright they are painful to look directly into and will momentarily leave spots before your eyes.
  9. Warm white LED’s can even simulate the homey glow of good old fashioned incandescent bulbs (if you’re nostalgic for that kind of thing).

So LED’s are the perfect light source, right? Not quite, they still have a few restrictions that make them problematic in a few applications.

  1. LED’s are very directional. Like a spotlight, they cast a cone of a certain angle across a surface. Newer LED’s are getting better at broader cones, but you still cannot light a whole space with a single unit. If you examine the new LED house light bulb replacements, you will see that the makers get around this problem by using a bunch of LED’s each pointed in a different direction. We alleviate some of this by diffusing windows or even frosting the LED’s lens.
  2. Most small LED’s are sensitive and need their current restricted to keep from burning out. This means that the user must be very careful in selecting and installing correct resistor values in circuits. Equal care must be taken during soldering to not overheat the component. Always check the data sheet that comes with the component.
  3. Most LED’s operate in a limited range of voltages. Too much and the LED burns out. Too little and the LED will not light. This makes dimming LED’s difficult. The best method uses pulse width modulation (PWM), which requires additional electronic hardware to switch the LED on and off very quickly.
  4. Like all diodes, LED’s are directional. They have a plus and a minus pole. Install them backwards and they simply don’t work. Reverse them and they’ll be fine.

All in all, SMARTT  has almost entirely moved to LED’s for our lighting needs. Many manufacturers make them and pre-designed multi-LED modular units set for common voltages like 12 V or 24 V make lighting structures a breeze. Gone are the worries of breaking a fragile light bulb or even more fragile Cold Cathode tube. As long as the electrical connection is properly made they will light for years to come.

When SMARTT  installed the layout at the California State Railway Museum, the toy collection for which our layout was the centerpiece was entirely lit by LED strip lights to protect the exhibited toys from dangerous deteriorating effects of regular light and heat.

One recent client had his entire layout room decked out with ceiling mounted LED track lighting which, when used with special PWM equipment can simulate any color of visible light for any kind of outdoors time, day or night.

Even size isn’t an issue. Forget grain’o’wheat bulbs. A few LED’s I saw the other day might be better described as grain’o’dust!  Of course special equipment and handling is required for using these tiny surface mounted lights, but with a little imagination and skill, LED’s will find their way into your every project. Briefly, their low power demands, large color variety, durability, and long-life, make LED’s the “go-to guy” of the lighting world. For now, at least, LED’s are the future of light.


from the October, 2011 SMARTT Newsletter

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