We have all heard that LEDs (light emitting diodes) will soon replace traditional incandescent light bulbs and the more recent CFLs (compact fluorescent lamps). But until recently, LEDs have been relegated to commercial or specialized use due to expense.
Now, LED bulbs are better and cheaper and are already cost-competitive when length of service is taken into account, though it might be as well to wait a little longer as prices are falling fast.A great deal of information can be found online, but much of it is specialized and may not be helpful to the average consumer. This guide hopes to correct that.
When shopping for LEDs, this is what you must consider:
Direction of light
Whether the bulb is dimmable (if needed for its intended application)
Whether the bulb is rated for outdoor use (if it will be exposed to weather)
Whether the intended application will allow the bulb to shed sufficient heat
In laymen's terms, a lumen is roughly the amount of light given off by one candle. Color temperature is measured in Kelvins (K), and for our purposes describes the color of the light. Direction of light is important because unlike traditional bulbs LEDs emit light in just one direction. This can be partly resolved because each LED bulb actually has many diodes pointed in one or more directions in various arrangements. Consumers will have to get used to getting the bulb that best suits their needs for a particular application. Whether a bulb will be put on a dimmer switch or used outdoors exposed to weather will also need to be taken into account as not all LED bulbs are suitable. Finally, one will immediately notice the cooling fins on all the LED bulbs, and will have to consider whether the bulbs will get sufficient air flow to keep the bulb cool when in operation. This should not be a problem with most indoor lights, but naturally don't use one of these as an appliance light in an oven or dryer, or in an airtight fixture such as might be over a shower.
We are used to choosing bulbs based on wattage, but this is a problem when it comes to LEDs for two reasons: first, because wattage is a measure of energy used and such comparisons are meaningless with improvements in efficiency; and second, because even incandescent bulbs of a particular wattage can vary considerably in light output, depending — for example — on the thickness of the filament (thick filaments last longer and are used in hard service bulbs, but put out less light).
Still, it is useful to have a rough comparison - Watts and Lumens:
An important safety consideration: if a fixture is rated for a certain wattage, use the equivalent lumen rating in the chart above when deciding what size LED bulb can be used in that fixture.
Color temperature can make a big difference. I replaced some 800 lumen/2700K (estimated) CFLs in a ceiling fan fixture with 450 lumen/3000K LEDs — and was surprised that the room seemed noticeably brighter. Most of the available stock in stores seems to be 2700K or 3000K, but a few 5000K bulbs should also be available in most places — and other color temperatures can be found online. Color temperature is partly an aesthetic choice, but I personally find that a 5000K bulb makes a room much cheerier and easier to see in.
Direction of light is a factor that very much depends on the application. Most of the bulbs in stock put out light primarily in one direction, and these are suitable for downlighting, ceiling fans, track lighting, and the like — and will actually be more efficient in these applications as they will waste less light in directions that are not useful. These are also suitable for hallway lights where one does not necessarily have to have first-rate lighting. However, these will not be useful for table lamps or the like. Table lamps will require what are called omnidirectional bulbs. Look for it on the packaging.
That concludes the most important factors to consider about LED lighting, and casual readers may stop here — but for those wishing to know more:
The explanation for why LEDs have problems with heat, despite being far more efficient than incandescent bulbs, is this: incandescent bulbs and LEDs both generate far more heat than visible light, and incandescent bulbs generate far more heat than LEDs, but incandescent bulbs emit most of that heat as infrared light which is not visible to humans, thus solving the heat dissipation problem. Curiously, this means that the bulb portion of an LED is actually cooler than an incandescent, but LEDs still have trouble shedding heat.
A more complete list of the advantages and disadvantages of LEDs:
Highly efficient (much more efficient than incandescents, slightly more efficient than fluorescent)
Long life expectancy (50,000 hours or more before significant dimming)
High quality of light (no flickering, pretty good spectrum)
Can produce white light ranging from yellowish to bluish (and much more)
Produce less heat for the amount of visible light, which means lower cooling costs
Quiet operation (unlike fluorescent)
Turn on instantly (unlike fluorescents)
Color-changing bulbs are available (and pretty neat)
Have difficulty shedding the heat they do produce
Sensitive to heat
Some models cannot be used with a dimmer switch
Output is directional (an advantage in some circumstances)
Expensive (though prices are rapidly falling)
Low power factor (typically ranges from .5 to .9 depending on the model - 1.0 would be perfect - this slightly reduces efficiency)
Output decreases over time
Some qualifiers: Regarding longevity, of about 30 bulbs I have experimented with, two have failed. One simply stopped working despite very low wattage and relatively low use over several years, the other (a well known international brand) simply burned up, despite having plenty of access to air, and left scorch marks on the socket.
Most models offered for sale in stores are now dimmable, but do check the packaging to be sure. As always, dimming light bulbs reduces their efficiency, so consider whether you could get the same effect by turning off some of the lights rather than dimming all of them. LED lights will not dim as far as incandescent lights will, but might dim to half their usual brightness.