Growing up as LED lights come of age
Over the years Alan Finkel's appreciation of the efficient and versatile LED light has deepened.
Two years ago we changed all the halogen ceiling lights in our home to light emitting diodes (LEDs). What joy! Our LEDs are brighter than the lights they replaced, they use less electricity, they mimic the colour of sunlight, they have not visibly aged since they were installed, they work with dimmers and they are safer in the ceiling cavity because they do not run nearly as hot as the halogens.
Like a distant uncle I have watched LEDs grow up from a tiny plaything to the workhorse of modern lighting.
I was too young to appreciate them when the first commercial LEDs were released in 1962, but by the early 1970s I was assembling electronic gadgets out in the garage, where I kept red LEDs about half the size of a pea as part of my stock of electronic components. I still have an ornament I made that consisted of LEDs mounted on the tip of long plastic wires like red eye stalks, each blinking to its own private rhythm.
Sometime around then I purchased my first digital watch, the amazing Pulsar with numbers made up of tiny LED dots.
Later, as an engineer in a company designing scientific research apparatus, I used LEDs as front-panel indicators. They were barely visible in a brightly lit room so for anything important we used incandescent bulbs.
During the 1970s and 1980s, LEDs gradually became brighter and red was joined by amber, green and eventually blue in the mid-1990s, at which point LEDs replaced incandescent lamps as indicators on panels fronting appliances from ovens to audio amplifiers.
LEDs last for many years, even when heavily used, partly because they are “cold” light sources in which the light emission is a subatomic process that does not rely on heat.
In contrast, in a halogen or conventional incandescent bulb, the light comes from the glow of a tungsten filament heated to white hot. At those temperatures the filament slowly vaporises, hence their relatively short life.
This year’s Nobel Prize for physics was awarded for the invention of the blue LED (see A blue light that might save the world). Blue LEDs are essential for the use of LEDs in television screens and ceiling lamps.
In LED televisions every pixel is made up of tiny red, green and blue LEDs. By varying the intensity of the individual LEDs, millions of different colours can be generated, including white.
But this is not an efficient way to create a white-light ceiling lamp.
For that, a blue LED or its close relative, an ultraviolet LED, illuminates a phosphor coating that converts the single colour emitted by the LED into the broad spectrum of colours in white light. Even so, it took a long time to reach today’s high efficiency levels. In 2008 I replaced all the halogen ceiling lights in one room with LEDs, inadvertently turning the room from a cheerful place and giving it the harsh, cold light of a morgue.
I hastily restored the halogens. Over the years I kept trying the latest LED offerings, but they were too blue, too purple, too pink or too dim.
Finally, in 2012, they came of age. Their absolute power was up, their efficiency was up, and they were able to generate light with the attractive colour referred to technically as “2700K” and colloquially as “warm white”.
The designator 2700K refers to the temperature in degrees Kelvin of a heated tungsten filament whose radiation would produce the same shade of white. The best of the commercially available LEDs are now many times more efficient than halogens and conventional incandescents, slightly more efficient than fluorescents, and still improving.
Their first public use of which I am aware was in traffic lights. Now LEDs are used for torches, street lighting and giant billboards where the “afterglow” of shampoo commercials can make city intersections as bright as day.
LEDs will continue to improve. Today’s emit about 90 lumens of light per watt, which corresponds to 13% efficiency at converting electricity into light. The best examples in the lab are nearly twice as good as that.
LEDs are transforming lighting in every field, using less electricity to produce better light.
It cannot be long before most other forms of lighting become obsolete.
If you haven’t already made the change, do so at the next opportunity.