(and can save you a lot of money !)
During the last 10 years there has been a silent revolution in electric lighting. Before that, the most common light bulb in most peoples houses was the pearl 60 watt BC lamp (BC stands for ‘bayonet cap’, so called because it resembles the fitting on the end of a Lee-Enfield rifle which was there for fixing a bayonet to). In rapid succession we have moved through halogen lamps, CFLs (compact fluorescent lamps), to the ubiquitious LED, which is now fast becoming the standard, even for car headlights.
You might think the LED is a modern invention, but the phenomenon was first observed over 100 years ago, and LED lamps were commercially available when I studied electronics at university 50 years ago. What has changed is the wide range of light colour and the incredible efficiency that is now available. In the 1960s, LED lamps were only used is indicator lamps in electronic equipment, and no-one dreamed they would one day be used for household lighting. The change has been possible because of the development of new semiconductor materials, such as gallium nitride.
Colour
Many of the new LED lamps are now sold as white, warm white, or cool white. The cool white ones tend to be slightly more efficient, but none of them give exactly the same light as an incandescent lamp. This because the light is actually produced by blue or ultraviolet LEDs shining on a yellow phosphor background. Some pictures or coloured articles can look slightly different when viewed in natural daylight.
Lifetime
LED lamps last around 25,000 hours, which is about 25 times as long as the traditional 60 watt pearl lamp. If they are switched on for 4 hours a day, that means you might expect them to last about 17 years. The light output decreases slightly as the lamp ages, but you are unlikely to notice this. Curiously, LED lamps are more efficient when it is cold, which makes them ideal for outdoor lighting.
Comparing Efficiencies
EU legislation now requires that lamps are marked to show the visible output in lumens, rather than the power it takes from the mains in watts. This is a bit confusing, because we are not used to lumens, but it helps to remember that the old 60 watt pearl lamp produced about 700 to 800 lumens of visible light. As a rough comparison, to get the same amount of light using other lamps, you would need a 45 watt halogen lamp, a 13 watt CFL, or a 10 watt LED.
Be Warned !
Many of the people who sell LED lamps make rather ambitious claims, saying that a lamp producing 360 lumens is equivalent to a 60 watt incandescent lamp. It is not ! If you’re buying lamps, always look for the light output in lumens, remembering the comparison above. Be aware also that not all lamps can be used with a dimmer switch.
Lamp Jargon
Some of the most common LED lamps are those which fit into a fitting recessed into the ceiling. Unfortunately there are are plethora of confusing terms and abbreviations used with these and the halogen lamps which preceded them:
MR16 means a multifaceted reflector, with a lamp diameter of 16 eighths of an inch, or 2 inches (51mm).
GU10 is also a Glass lamp with 2 pins separated by 10mm which lock into position with twisting action. This really applied to halogen lamps, but is now used for LED lamps which use the same base.
PAR16 stands for parabolic aluminised reflector, with a lamp diameter of 16 eighths of an inch, or 2 inches (51mm). It is now sometimes used to describe a LED lamp which fits the standard halogen fitting.
SMD means a lamp where the individual LEDs are mounted directly onto a substrate surface. These were the most common until recently.
COB (chip on board) is the latest LED technology which enables the individual LEDs to be placed closer together giving a more uniform appearance and slightly more light output.
Savings and Prices
Its very difficult to predict the savings you can make by switching to LED lighting, because it all depends on how much you use your lights, but they could reduce your electricity bills by about 20%. That means you could expect to recoup the higher purchase cost of LED lamps within about 6 months.
Unlike many products, the price of LED lamps keeps falling. The best prices tend to be from online suppliers, but can vary widely. At the time of writing (January 2015) a 5W GU10 COB LED should not cost more than £5.
Geoff Clemerson