Pros and Cons of LED Lights

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In principle, LED light bulbs sound ideal. The efficiency of an LED is radically superior to that of traditional filament light sources, and the cost of raw components keeps decreasing. Yet, designers encounter a number of challenges in actually implementing this technology.

Heat Produced from Light Bulbs

One of the qualms we have with traditional filament light sources is the heat emitted.  A standard 100W light bulb tends to emit only 10W of light and loses the other 90W as heat.  However, because the filament needs to heat up in order to emit light, the heat generated actually helps the efficiency of the light.  Many traditional light fixtures like those used for recessed ceiling lighting are designed to insulate the bulb and keep as much heat at the source as possible.

LED Thermal Management

LEDs operate in the same way, as most semiconductors decrease in performance as heat increases, so retrofitting a fixture is often not as simple as swapping out a tungsten bulb with one using LEDs.  Most lights require additional thermal management to eject the heat out into the ceiling to keep the LEDs from burning out.  LEDs are known for their incredibly long lifetimes (60,000+ hours is standard) but will only last a fraction of that amount of time if subjected to stressful thermal conditions.  Though LEDs are much more efficient, they still emit about 30% of their power as heat.  An industry rule of thumb is to allow 4sqin of heat sink for every watt of power to dissipate, so a 13W LED source replacing a 100W tungsten source (both giving 10W of light) will need about 12sqin of heat sinking into free air – more if the fixture is insulated by surrounding materials.

What is a LED Filament Bulb?

Filament bulbs are really just classed-up versions of the original light source – fire.  They are optimized to run on 120VAC in the US simply because that is what comes out of the wall.  These bulbs emit light by getting hot, and that can be achieved with just about any power source.  LEDs are much more particular. 

Standard Lighting LEDs

Standard lighting LEDs are constant current devices that require about 3 volts DC to turn on and prefer to run at about 350mA.  This current must be established and regulated by a driver that can take 120VAC from the wall.  Converting from 120VAC to 12VDC tends to require large inductors and capacitors, and creating a constant current output also requires specialized circuitry.  The result tends to be a simple PCB with just a handful of inexpensive LEDs attached to a cacophony of a driver, crammed into a standard light bulb form-factor like the classic A9 bulb.  

This driver consumes the space that would logically be used for heat sinking and instead generates additional heat that may shorten the lifetime of the LEDs.  Because cost is such a barrier to entry for many customers, these drivers tend to value cost over efficiency and reduce the overall quality of the bulb. 

LED Color Quality

Filament bulbs emit all wavelengths of light because like the sun, they are burning.  LEDs rely on the energy emitted across a diode and therefore can only generate one wavelength per material.   There is no one wavelength that can replicate what we see as white light, so these die typically emit a wavelength in the blue area of the spectrum that is converted to a white light through a phosphor conversion layer.  This works fine for situations that simply require illumination, they cannot recreate the warmth and depth of color rendered by a traditional bulb. 

Reds in particular suffer under the cool light generated by most LEDs, causing skin tones and foods to look washed out and unappealing.  LED bulb manufacturers combat this drawback by using LEDs that can produce warmer light by sacrificing efficiency, or even mixing small amounts of red LEDs into a design. 

Though LEDs can be a wonderful choice for new and custom lighting designs, they are a difficult technology to use in retrofit applications.  If you are replacing your filament bulbs with LEDs, keep the challenges in mind and be aware that you get what you pay for in LED bulbs.  If you are putting the bulb in an insulated ceiling can, it may be worth buying a more expensive bulb with a higher efficiency to avoid having to replace a burned out bulb down the road.  

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