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Lamps using traditional and halogen incandescent light bulbs both work by heating a tungsten filament encased in a vacuum to extremely high temperatures causing the filament to emit visible light. Incandescent light bulbs are the most common types of bulb for lamps in homes and commercial buildings, although the traditional incandescents which have been used for over a century are currently being phased out by governments around the world.
Light Emitting Diodes (LEDs)
Light emitting diodes (LEDs), on the other hand, are a form of solid-state lighting (SSL) that work by moving electrons through a solid semiconductor material, usually aluminum-gallium-arsenide (AlGaAs). Due to their low energy consumption, small size and ability to switch on and off almost immediately, LEDs have been used for indicators and displays since the 1960s. More recent advances in LED technology have led to their increasing use in a diverse number of applications such as medical, aviation, automotive, plant growing and even building and outdoor area lighting.
LEDs typically last twenty-five times longer than traditional incandescent light bulbs, and over eight times longer than halogen incandescents (Energy.gov, 2012). This is due to heating of the element causing a material deterioration of the tungsten filament in incandescent bulbs. Eventually, the tungsten deteriorates completely and the bulb suddenly burns out. While this deterioration is slowed by the addition of an inert gas such as argon to the bulb’s vacuum, it still means changing light bulbs is at best a time-consuming chore in domestic settings, and at worst a sizeable cost in commercial maintenance budgets.
While LEDs on the market today last much longer than incandescent bulbs – as well as compact fluorescent lights, the other energy-efficient lighting solution promoted in favor of incandescents – they are still prone to deterioration. Unlike incandescents which burn out at the end of their life, LEDs gradually deteriorate over time. This gradual deterioration in LEDs is referred to as degradation.
Degradation in LEDs
Degradation in LEDs is caused by a number of failures in their multiple components. Packaging failures include epoxy degradation, where the plastic casing discolors due to heat, and differentiated phosphor degeneration, where different phosphors in the casing degrade at different rates from heat and age and cause the LED to change color.
Semiconductor failures include dislocations which nucleate and grow in the crystal structure of the metal LED semiconductor, accelerated by light emitted by the LED, ambient heat or especially high current densities. Some types of semiconductor material are less susceptible to dislocations than AIGaAs, such as gallium nitride (GaN) and indium gallium nitride (InGaN). Dislocations can also be caused by electromigration, which can move atoms in the semiconductor away from their active regions and is a result of high current density.
Sometimes sudden failure can also occur in LEDs and is primarily caused by imperfections in the diode due to manufacturing tolerances. Sudden failure can be caused by short-circuits in the LED electronics due to whiskering and electrostatic discharge (ESD), which can also lead to the LED degrading at an increased rate.
While these factors all contribute to a gradual degradation of LEDs over time – or, rarely, to sudden failure of an LED – this degradation only decreases the visible light produced by the LED by 30%. While this is a significant loss of light production, it is in most cases imperceptible. This is due to the gradual nature of LED deterioration, and therefore it is usually only noticeable when comparing a new LED bulb to a bulb which has degraded over up to 50,000 hours of use.
The long lifetime and gradual nature of LED degradation make LEDs a better option for lighting than traditional or halogen incandescent bulbs, which will fail suddenly and after a much shorter period of time.
Sources and Further Reading