WHAT ARE LEDs?
Some Colourful LEDs
Picture Courtesy of fusion_online
What Are LEDs
What does LED stand for? Light Emitting Diode. A Diode is two (di) tiny pieces of semi-conductor material at the very centre of the LED. Wow, are they emitting some light or what?
The Sub-Atomic Physics
Semi-conductors are halfway between electrical Conductors and Insulators. Conductors are Copper and most other metals. Insulators include Rubber, plastic and Ceramics.
One layer of semi-conductor material will have electrons to spare. The other will have a shortage of them. The excess of electrons on one side is not able to flow to the side to fill the deficit. If we apply a suitable electric current to give it a little boost, this changes
Once the electricity is available, a build-up of electrons is able to rush to fill the holes on the other side. In doing so emit photons — light!
Images Courtesy of YouTube & Luxeon
The power source replaces the electrons that have ‘popped’ into packets of light. Thus the LED produces a steady flow of even light with very little power consumption.
Incandescent Light Bulbs
The old-fashioned electric light bulb was first patented by Thomas Edison in 1879.
He used carbonised cotton thread as a filament. that he heated until it glowed.
Edison knew that of all the element tungsten had the highest melting point. But it wasn’t until over 30 years later that a method for making filaments from it came about.
The General Electric Company patented it in 1911. They used ductile tungsten wire to make filaments for incandescent light bulbs.
Manufacturers used Tungsten thereafter for their light bulbs. They held sway for a century or so from then on. They produced light by heating a filament of tungsten until it glowed white-hot. Burning it. Of course, with the best will and technology in the world, they “burnt out” sooner or later.
By contrast, LEDs produce light at a sub-atomic level. In a similar way that the transistor amplifies sound and revolutionised the radio.
What the Transistor Did for Radios
Back in the 1960’s the advent of the transistor revolutionised radios.
They had been bulky and heavy pieces of furniture. People called them ‘wirelesses’ because of no physical joining of Transmitter and Receptor. But their Mains Leads tethered them to a wall socket. Plus an aerial up in the loft.
Old-School Radios produced a considerable amount of heat from their Valves. They were incandescent, like Edison’s light bulbs. They had to have ventilation slots in the back, to dissipate the heat. Transistors, like LEDs, produce hardly any heat.
Because the transistor required much less power, batteries became viable. Thus hand-held, fun-coloured plastic-cased ‘trannies’ started to appear. They had telescopic aerials, People took them on picnics, to the pool and beach. They became part of the Sixties ‘Flower-Power’ Revolution!
The Advantages of LEDs
LEDs are over 80% more efficient than yesteryear’s luminescent bulbs.
Households in the UK spend about ?590 a year on electricity consumption, on average.
Of course, not all electricity consumed is by lighting. But it is clear that this modern technology offers considerable savings for everyone.
If you replace incandescent, fluorescent or halogen lighting, with LEDs. you will reduce your electricity bills. Once you have paid off the initial bulb replacement costs you will save money
The EU ban on halogen bulbs (despite Brexit) came into force on 1st September 2018
It is not possible to be precise about the ARL(Average Rated Life) of LEDs. They are new and many of them are still going strong!
The ARL is how long it takes for half of a given number to pop.
So, if we test 100 bulbs and 50 of them fail within a couple of months their ARL will be 1500 hours (62.5 days).
That’s a typical value for incandescent lamps. Of course, some bulbs will fail sooner, some will take longer.
The ARL is set under normal conditions. If you use the bulb above an oven (hot), in a freezer or outdoors in Winter (cold), it may fail sooner than its ARL.
You may also shorten its life if you expose it to rain or near a sprinkler or shower (wet). The same near a door that gets slammed or machinery (vibration)
The ARL of LEDs is at least 3 to 5 years.
Out-of-date type light bulbs only convert a mere 1/10thof electricity into visible light.
If you have burnt your fingers replace a just-burnt-out light bulb, you’ll know how hot they can get! 90% of the energy Input to incandescent is burnt as heat.
Of course, it is much less likely that you’ll have to replace a LED bulb because of their longevity.
If you do have to remove one for maintenance or cleaning it will still be cool to the touch, even if it has been on for hours.
Don’t Contain Toxic Chemicals
Compact CFC (Fluorescent) light bulbs contain Mercury. It’s a very toxic chemical, This makes disposal problematic. In contrast, LEDs do not contain any Mercury at all.
The micro mini Twist CFL is the smallest CFL (‘Compact’ Fluorescent) Light bulb around today. Its a is a twisted 0.635 cm (1/4″) tube, that’s roughly 9.4x5x5 cm (3.7x2x2″) in size.
In contrast, Capsule LEDs are tiny, 50x16x16mm (2×0.5×0.5″), small enough to insert into the surface of a mirror.
LEDs are very long-lasting, because of their tiny size and solid construction. Incandescent bulbs are prone to shatter. This can send thousands of thin, sharp shards of glass flying in all directions.
You can focus, or collimate the light from LEDs into a coherent beam with a particular direction.
You can use this for Torches, and Laser Pointers. Also Heads Up Displays for Flight Simulators plus Museum and the Display Lighting.
The light from incandescent and fluorescent sources is incoherent. It goes in all sorts of directions
With LEDs, you not only make significant savings in energy costs. You also reduce replacement and other maintenance costs, compared to incandescents and fluorescents.
LEDs in the Home
LEDs have increasing applications in the home. Increasingly overhead and sidelights in the home are being fitted with LED bulbs. They are appearing in the Home in general, the Kitchen, the Bathroom and in particular the LED Mirror.