An LED is a light-emitting diode. LEDs consist of a
semiconductor diode that emits light when a voltage is applied to it.
LED technology has been used for several decades as indicator lights for
electronic devices and now is useful in lighting technology.
How are LEDs used?
LEDs are historically popular with architectural
highlighting. Red, Green, and blue LEDs are commonly used for traffic
lights and exit signs. Currently, the LED has evolved and can be used in
indoor and outdoor lighting fixtures.
Have LEDs always been used in general illumination lighting?
LEDs have not always been used for general lighting. Experts
have tested and created LEDs to ensure that lumen-per-watt ratio is at
least as good as existing technology and that the color quality meets
industry standards. The lighting industry can now offer products for
general illumination, indoor and outdoor lighting.
How has new LED technology improved?
LED technology is rapidly evolving, showing significant
promise in efficiency, color consistency, color quality, and in the
ability to produce more reliable light over time. As the technology
improves, the ways that LEDs can be used for general illumination is
expected to expand.
What are the advantages to using LED lights?
High efficiency and durability are the most pronounced
benefits of using LED lights. Longer lifespan and low maintenance helps
you save energy and money as you invest in LEDs for your lighting needs.
What's the difference between efficiency and efficacy?
Efficacy applies to input and output of units. We measure the
amount of light (lumens) produced by a certain amount of electricity
(in watts). Efficiency refers to the ratio of the total lumens released
from a fixture to the total lumens produced by a light source.
How are LED products evaluated?
Evaluating an LED product can seem complex. One must consider
the overall system efficiency, optical control, thermal management, and
luminosity, and at what point in time the fixture will reach 30 percent
Coal-fired power generation accounts for roughly 40 percent of the mercury emissions in the U.S.
The department of energy concluded in its solid-state
lighting (SSL) commercial product testing program:
"Until the field of SSL technologies and supporting knowledge matures,
any claims regarding performance of SSL luminaires should be based on
overall luminaire efficacy (i.e., from testing of the entire luminaire,
including LEDs, drivers, heat sinks, optical lenses and housing), to
avoid misleading buyers and causing long-term damage to the SSL market."
What is junction temperature?
Junction temperature is the temperature at the point where an
individual diode connects to its base. Maintaining a low junction
temperature increases output and slows LED lumen depreciation. Junction
temperature is a key metric for evaluating an LED product's quality and
ability to deliver long life.
The three things affecting junction temperature are: drive
current, thermal path, and ambient temperature. In general, the higher
the drive current, the greater the heat generated at the die. Heat must
be moved away from the die in order to maintain expected light output,
life, and color. The amount of heat that can be removed depends upon the
ambient temperature and the design of the thermal path from the die to
The department of energy advises: "Heat management and an
awareness of the operating environment are critical considerations to
the design and application of LED luminaires for general illumination.
Successful products will use superior heat sink designs to dissipate
heat, and minimize junction temperature. Keeping the junction
temperature as low as possible and within manufacturer specifications is
necessary in order to maximize the performance potential of LEDs."
Why Does Thermal Management Matter?
LEDs release heat that has built up inside a fixture, using a
low junction temperature and innovative engineering. The heat flows out
through a heat pipe assembly which can preserve the life of your LED.
Some products releases warm air while circulating cooler air through the
fixture using airflow convection technology. Look for products that
assist in saving heat and helping you save money.
Why is the lifespan of an LED measured as lumen depreciation?
An LEDs lifespan is measured by lumen depreciation because
most LED light sources will decrease in light output over time rather
than burning out like other technologies. Some LEDs can burn out but
most just grow dim over time. The industry measures the decrease of
light output (lumen depreciation) to inform consumers of the amount
light to be emitted from an LED fixture or bulb.
The Illuminating Engineering
Society's (IES) current standard recommends that lifetime of LED lights
be based on the point where the product loses 30 percent of its initial
light output. This is called the L70, meaning the estimated point where
the LED light produces only 70 percent of its initial light output.
There are other industry methods for estimating lifetime that take other
things into consideration but this is the most widely accepted.
LED lifespan refers to the point at
which it has reached 30 percent lumen depreciation. At 50,000 hours an
LED burns on a decreased lumen output.
What is equivalent to 50,000 hours as a fixture is illuminated?
24 hours a day, 5.7 years
18 hours per day, 7.4 years
8 hours per day, 17.1 years