Benefits and drawbacks of LEDs
Lifetime
As solid-state light sources, LEDs have very long lifetimes and are generally very robust. While incandescent bulbs may have an expected lifetime (to failure) of 1000 hours, LEDs are often quoted of having a lifetime of up to 100,000 hours - more than 11 years. However, this figure is extremely misleading; like all other light sources, the performance of LEDs degrades over time, and this degradation is strongly affected by factors such as operating current and temperature.
At present, there is no standard definition of lifetime for LEDs, although various parties have suggested that lifetime should be the time taken for the LED’s output to fall to some percentage (such as 70% or 50%) of its original value.
Standardization
The general lack of standardization in the LED field is an ongoing issue. Various standards relating to LEDs exist in areas such as automotive lighting and traffic signals. Other efforts are being conducted by bodies such as CIE, NEMA and IES.
Low maintenance
The long lifetime of LEDs reduces the need to replace failed lamps, and this can lead to significant savings, particularly in the cost of sending out maintenance crews. This also makes LED fixtures useful for installation in relatively inaccessible locations. However, if tasks like cleaning the light fixture or performing electrical checks need to be carried out regularly, then the light sources could be replaced at the same time, negating the "low maintenance" advantage.
Efficiency
LEDs are high-efficiency light sources. White LEDs with efficacies of 25 lm/W and up are commercially available, exceeding the performance of incandescent and some fluorescent sources. The directional nature of light produced by LEDs allows the design of luminaires with higher overall efficiency.
Low power consumption
The low power consumption of LEDs leads to significant energy savings that can often drive the installation of LED-based systems, for example traffic signals. National programs to develop effective solid-state lighting industries in the US and Japan have been driven by the potential energy savings associated with using LEDs.
Brightness
Although LEDs have high efficiency and consume a small amount of power, the devices produce a small total number of lumens. For example, a 60 W incandescent bulb with an efficiency of 20 lm/W produces 1200 lumens. A one-watt LED with an efficiency of 30 lm/W produces only 30 lumens i.e. 40 such LEDs are required to produce the same amount of light as the incandescent bulb.
Heat
LEDs don't produce heat in the form of infrared radiation, which makes incandescent bulbs hot to the touch. The absence of IR radiation allows LED fixtures to be positioned in locations where heating from conventional sources would cause a particular problem e.g. illuminating food or textiles.
However, LEDs do produce heat at the semiconductor junction within the device. The wall-plug efficiency (optical power out divided by electrical power in) of LED packages is typically in the region of 5-40%, meaning that somewhere between 60 and 95% of the input power is lost as heat.
Without very efficient thermal management and heat sinking this causes the junction temperature of the LED to rise, which causes the LED characteristics to change. Driving LEDs above their rated current causes the junction temperature to rise to levels where permanent damage may occur.
Cost
In many applications, LEDs are expensive compared with other light sources, when measured by metrics such as “dollars-per-lumen”. LED manufacturers continue to work towards reducing their production costs while at the same time increasing the light output of their devices.
However, the high initial cost of LED-based systems is offset by lower energy consumption, lower maintenance costs and other factors.
11/06/2012