A view of the world from my own unique perspective

LED Lighting Technology

Fellow Toastmasters – we are on the threshold of a lighting revolution. LED lighting may not be on your radar just yet, but it will be soon. It’s an emerging technology, and will play an increasing role in our lives during the coming years.

Until recently, light bulbs have not changed much since Thomas Edison placed a carbon filament in an oxygen-less bulb. Of course the filament is now tungsten, but the principle remains the same: put a filament in a bulb and fill it with an inert gas. Then run an electric current through the filament; its resistance will cause it to heat up until it becomes white hot. The problem with this method is the lack of efficiency. 95% of the energy in an incandescent light bulb is used to heat up the filament – the light that it gives off is just a side effect!

During the past few years, a new type of light has entered the market: compact fluorescent, or CFL bulbs. They are a good choice for general purpose lighting, because they offer many advantages:

  • Lifespan: They last longer – CFLs between 6,000 and 15,000 hours, compared with 1000 hours for an incandescent.
  • Temperature: Incandescent bulbs have a piece of white-hot metal inside them, and the bulb is generally too hot to touch. CFLs are cool to the touch.
  • Efficiency: The most heralded advantage is their energy efficiency. CFLs use one quarter of the energy to produce a same amount of light and an incandescent bulb.

There are of course, some disadvantages to compact fluorescent bulbs as well.

  • Size: Like all fluorescent lights, CFLs require a ballast. This makes the bulbs larger than incandescent, and generally too large to be used in flashlights.
  • Fragile: Like incandescent bulbs, CFLs are made of glass, and can break easily. They can’t be used under rugged conditions because they’re just too fragile. In fact, they’ll break more easily than a standard flashlight bulb because they are much larger.
  • Mercury: If a CFL shatters, then shards of broken glass will be the least of your concerns. As you know, CFLs contain mercury, so if they do break, not only will you have shards of broken glass all over the place, you will have to contend with mercury vapour in the air. I did a little research on the net and discovered what to do is a CFL breaks:
    • Clean-Up Procedure: If a CF bulb breaks then: Vacate the room and ventilate it for at least 15 minutes. Shut off the central air conditioning or forced air heating system. Do not use a vacuum cleaner, but clean up using rubber gloves and aim to avoid creating and inhaling airborne dust. Sweep up all particles and glass fragments and place in a plastic bag. Wipe the area with a damp cloth, then add that to the bag and seal it. Mercury is hazardous waste and the bag should not be disposed of in a garbage can.
  • Disposal: Even if a CFL doesn’t break and you are able to use it for its entire lifespan, there is also a disposal problem. You can’t throw them in the garbage, they can’t be recycled in a blue box, and because of the mercury they should never be incinerated.

I’d now like to talk about an up-and-coming lighting technology: LEDs. LED stands for Light Emitting Diode. A diode is an electrical component that allows current to pass in only one direction. In a Light Emitting Diode, when the electrons pass through it, they jump a gap and then fall into a lower energy level on the other side. When this happens a photon is released. The wavelength of the light, which we interpret as its colour, depends on the amount of energy released as the electrons cross the gap. This is what a light emitting diode looks like [pass around packet of 5mm LEDs].

Indicators To Illumination: When LEDs were first introduced, they weren’t very bright at all, and were used mainly as indicators – power lights for electronic equipment, stereo indicators for receivers. However, recent advances in brightness and efficiency means that they are becoming bright enough to be used for illumination.

Emerging Technology: What makes LEDs exciting is that they are an emerging technology – they are still being developed and improved, so as their brightness and efficiency increases, new applications for them are always being discovered. They may sound esoteric, but you’ve probably encountered LED lighting more than you realize.

  • LED Traffic Lights: Most traffic lights now use LEDs instead of incandescent bulbs. You may have noticed that traffic lights are now brighter, and their colours are more saturated. The next time you’re stopped at a red light, look closely at it – you should be able to see a grid of small LEDS instead of a single light source. In addition to using less power, LEDs save the city money because they last between 50,000 – 100,000 hours. The biggest cost isn’t replacing the bulbs, it’s sending a truck and a crew to each intersection.
  • Tail Lights: Some bus and truck taillights are LED – notice the grid patterns, rather than the single bulb. The next time you’re stuck behind a bus, take a look at its tail lights – you should also notice a grid pattern of LEDs.
  • Bicycle Headlights: [Show my bike headlight and pass it around]. This is the light I use on my bicycle – it’s a custom-made LED that’s brighter than any other bicycle light, with the exception of High Intensity Discharge lights. HIDs are brighter, but they consume far more power, and are incredibly expensive.
  • LED Candles: The women will probably disagree with me on this next point, but LEDs can improve your love life! Suppose that you want to impress your love interest by having a candlelight dinner. Candles are very romantic, but we guys are also a practical bunch and know that candles are also a fire hazard. They must never be left unattended. Therefore, the way to get the best of both worlds is to use one of these – an LED candle [turn on candle, pass it around]. This LED candle has all of the ambience, and isn’t a fire hazard.

When I say the word flashlight, most of you will probably think of this – a plastic flashlight that takes 2D cells that you probably bought at Canadian Tire or Radio Shack [show plastic flashlight]. This is what an LED flashlight looks like [show AAA-cell LED light]. Let’s put them side by side, so that you can see the difference.

Now let’s compare the light output. Here’s what the old Radio Shack flashlight looks like [turn on plastic flashlight, point toward sheet of white paper on table]. Now here’s the output of this tiny LED flashlight [turn on AAA LED light, point toward paper on table]. As you can see, there’s just no comparison.

And now, the most important question: if compact fluorescents are so popular, why would I want to consider using LEDs? Here are some of the advantages LEDs have over CFLs and incandescent:

  • Durability: Incandescent and compact fluorescent bulbs are both made of glass and can break very easily. LED lights are far more durable – you can drop an LED flashlight on the floor and the bulb won’t break. In fact, the flashlight housing will probably break before the LED does. Other than smashing one with a hammer, it’s very difficult to break an LED.
  • Lifespan: Incandesent bulbs last about 1000 hours; CFLs last between 6,000-11,000 hours. LEDs last between 50,000-100,000 hours. LED flashlights don’t come with spare bulbs because the light will last as long as you care to use it. That’s one less thing for you to worry about, and one less expense.
  • Operating Temperature: LED run cooler than incandescent bulbs because nothing inside them gets white hot. You can give a child an LED flashlight without worrying about breakage or burns. To be fair, there are some higher-end non-consumer LED flashlights do get hot, but they are deliberately driven beyond their design specifications.
  • Instant on / Instant off. Incandescent bulbs seem to turn on and off instantly, but they really don’t. It takes a few milliseconds for the filament to go from cold to white hot, and then a few seconds to cool down completely. Because LEDs turn on and off instantly, new functionality can be built into flashlights – like a strobe [demonstrate strobe mode]. This isn’t possible with an incandescent bulb because the filament can’t heat up and cool down quickly enough. These power surges will shorten the life of a filament, but will have no effect on the life of an LED emitter. Here’s another mode – S.O.S. [demonstrate S.O.S. mode]. Personally, I think this is the most useless mode on a flashlight – how many times do you envision yourself stuck on a remote island, anxiously waiting for a passing plane? This is a perfect example of “just because something can be done, doesn’t mean that it necessarily should be done”.

Variable Brightness Levels Das I mentioned before, LEDs are either on or off, which means 100% or 100% off. But as I showed you just now, that LED light had three different brightness levels. How is this possible? The answer lies in a piece of circuitry inside the flashlight, called Pulse Width Modulation, or PWM. The PWM circuit turns the LED on and off at certain ratios. If you want the light at half brightness, then the PWM circuit is set to 50% on, 50% off. The PWM circuit in this flashlight run at 100Hz, – that means that it turns the LED on and off 100 times per second, which means that you won’t notice any flickering at all.

Let me show you the PWM circuit in action. Let’s set this flashlight to its high mode – that means that the LED is on 100% of the time [spin light around horizontally on its keychain]. As you can see, the light makes a solid circular line as I spin it around. That indicates that the LED is always on. Now let’s set it to the medium setting [spin flashlight around again]. Notice the strobing effect of the light – it’s no longer solid, but in a series of spots. That’s the PWM circuit turning the LED on and off.

There’s a lot more to show you, but I see that I’m out of time. So let’s move on to the Q&A session…

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: