How to Extend the Service Life of LED Outdoor Lighting
By Gary Chan and Henning von Lepel*
can often cause the air inside the LED luminaire to rapidly heat
up, with the resulting higher pressure putting positive pressure
on the seals. As temperatures drop again at night, the internal
air contracts and creates a gentle vacuum, which draws the seals
inward. A quick drop in temperature can create a vacuum of up
to 150 mbar inside the luminaire, while a 30 °C change in
temperature creates approximately 10 percent of volumetric flow
of air in or out in a non-hermetically sealed enclosure.
Figure: Typical calculation of pressure differentials in a housing
Temperature Changes within LED Luminaires
Although LEDs do not get as hot as incandescent lamps,
switching a luminaire on and off nonetheless results in significant
temperature fluctuations. These are at their strongest immediately
after switching, which means that switching luminaires on and
off repeatedly puts not only the electronics but also the seals
under considerable strain.
Altitude Changes
When LED luminaires are shipped by air from their manufacturing
sites, the lamps will be subject to major changes in altitude, even
several times when the shipment involves intermediate stops.
This means LED luminaires are exposed to the difference in
pressure between a little over 1,000 mbar at ground level and
800 to 850 mbar in the aircraft.
Thermal Shock
A thermal shock occurs when a hot LED luminaire is sprayed
with cold water from a garden hose, for instance, or when a cold
luminaire is washed with hot water. It can also arise when a
luminaire encounters snowfall.
LED luminaires in outdoor use need to be protected from harsh
environmental conditions. The most significant stress factor
for the sealings of luminaire housings are pressure differences
caused by everyday temperature changes. In order to protect
the sensitive electronics inside, pressure variations have to be
equalized while preventing water and dust to enter the housing.
The most effective solution is a “smart venting element” with
a membrane that protects electronic housings against con-
tamination and fluids and provides air exchange and pressure
equalization at the same time.
For both commercial and residential applications standard
neon tubes and energy-saving lamps are increasingly replaced
by LED (light-emitting diodes) luminaires. The advantages of
LED lightings are numerous:
• They are fully RoHS-compliant (Restriction of Hazardous
Substances).
• They provide up to 85 percent energy savings in comparison
to conventional lamps.
• They can generate as much as 50,000 hours of light.
• They are one of the most environmentally friendly and reliable
solutions for outdoor lighting applications.
However, the service life of a LED is subject to the reliability
of the electronic components and power supply drivers, which
altogether make up the lighting system itself. This poses a
major challenge on LED systems for outdoor use. The housings
of the LED luminaires must be able to withstand the harsh
environmental conditions. To achieve this goal, the housing
of an LED lamp is sealed against the ingress of water and
contaminants. However, changes in outdoor temperature
cause the air pressure within the housing to fluctuate constantly,
which in turn puts either positive or negative pressure on
the seals and compromises their functionality. Over time,
seals begin to allow water and contaminants to enter the
housing, which can lead to corrosion, shorts, and potential
failure of the electronics. In addition, condensation on the
inside of the luminaire can impact the quality of its light.
Causes for Pressure Differentials
Temperature Fluctuations
Changes in outdoor temperature are one of the most common
causes of pressure differentials. These changes can be sudden,
for instance a strong thunderstorm on a hot summer day, or more
gradual over the course of the day or of the year. Either way, they
put significant stress on the seals. What is more, direct sunlight
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Typical Calculation
Pressure differential in a housing with 5 liters of free air
volume caused by a temperature drop from 65 °C to 15 °C
in 11 minutes.
Protective Vents
adhesive vents