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.

 

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Challenge: Equalizing Pressure

 

For maintaining constant pressure inside a luminaire it is crucial  
to allow air to flow freely in and out of the luminaire. The challenge 
is to block water and contaminants in doing so. Most types of 
seals to achieve this goal have multiple drawbacks as explained 
below:

•  Labyrinth seals are completely permeable to particles,  
  insects, and water. 
•  Rugged seals, additional bolts, thicker housings or potting    
  compounds for hermetically sealing the device require  
  the use of non-permeable materials and is relatively  
  expensive. Moreover, it makes the device heavier,  
  extremely difficult to open under negative pressure and  
  repair almost impossible. 
•  Felt elements and sintered vents address the pressure  
  differentials, but they can become blocked by water  
  and contaminants. 
•  A mechanical valve is a one-way solution from inside to  
  outside, which means it cannot prevent a vacuum.

Solution: “Breathing” Luminaire Housings 

Gore has developed a solution: a vent made of expanded polytetra-
fluoroethylene (ePTFE). A two-way breathable membrane continu-
ously equalizes pressure inside the luminaire housing while also 
preventing the ingress of water and contaminants. Equalizing 
pressure using an ePTFE vent reduces the potential for moisture 
vapor to condense on lenses and reflectors, and increases the 
service life of seals. The microporous membrane can be coated  
to provide oleophobicity. ePTFE’s node-and-fibril microstructure  
is open enough to allow gas molecules and vapor to pass through 
it easily, but the openings are so small that liquid and other  
particulates are repelled. Also, hydrogen sulphide is expelled  
this way.

Proper pressure equalization and water tightness have been 
demonstrated by thorough testing to compare two commercially 
available LED luminaires, one conventionally sealed unit and  

one with an ePTFE vent. Although the on/off cycle of both  
luminaires caused temperatures to rise and fall, the amount 
of pressure placed on the seals is significantly different. In the 
sealed luminaire, the pressure spiked by 6.2 mbar when the light 
was switched on and dipped -6.9 mbar when switched off. However, 
the vented luminaire showed a change of only ±0.69 mbar.

Figure: Impact of pressure on vented and unvented housings. 

Comparing the relative humidity inside the LED luminaires after 
a standard IPX5 water ingress test demonstrates the significance 
of pressure differentials. The relative humidity in the sealed 
luminaire was significantly higher than in the vented luminaire. 
Over the course of ten days, the relative humidity in the sealed 
luminaire almost always remained at around 100 percent.

Figure: The unvented housing shows relative humidity of 100%, indicating 
condensation.

This indicated condensation inside the luminaire caused by water 
entering during the test. Although the relative humidity in the vented 
luminaire rose immediately after the shock test, it decreased again 
relatively quickly and there was no evidence of condensation.

Figure:  
Luminaire with condensation

Important Consideration: Hydrogen Sulfide

Not only constant pressure is important for a long service  
life of an LED luminaire. Hydrogen sulfide is given off  
especially by inexpensive EPDM seals produced using  
sulfur vulcanization where not all the sulfur atoms were  
one-hundred per cent cross-linked. Sulfur vulcanized nitrile 
butadiene rubber (NBR) or other components containing 
sulfur can also give off hydrogen sulfide. This substance  
corrosion in luminaire components such as silver-plated  
leadframes, which could impact electrical contacts with  
the wire bond or die bond.

Impact of pressure on vented and unvented housings.

Relative humidity in vented and unvented housings.

   

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Comparison Test Proves  

Long-Term Protection

A further test, conducted outdoors over a period of five years south 
of Munich, demonstrated the longer service life of vented enclosures. 
Five units were tested: two with no vents, one with a side vent, one 
with a top vent, and one with two vents (one on each side). The 
testing showed that the pressure differential in the unvented units 
ranged from -150 mbar in both to 131 and 147 mbar respectively.

Figure: Long-term study of pressure differentials in electronics housings

A significant amount of condensation was also detected.  
In the vented units, the maximum pressure measurements fell  
to ±40 mbar with a top vent, ±30 mbar with a side vent, and  
just ±4 mbar with both vents. This is an impressive demonstration 
of how effective these venting systems are at equalizing pres-
sure. In addition, no condensation was detected, and neither 
was the ingress of water or dust. Further testing showed that 
the vents were fully functional even after five years of outdoor 
operation.

Figure: Long-term study of pressure differentials in electronics housings

Roundup: Venting Solutions Extend the 

Service Life of Outdoor LED Luminaires

Pressure differentials compromise housing seals. Not taking  
this into account when designing LED luminaires can reduce  
the service life of LEDs, power supply drivers and other  
electronics. The ingress of water through damaged seals also 
leads to condensation on lenses and reflectors that can  
decrease light efficiency and the aesthetic quality of the 
luminaire. As demonstrated through the IPX5 test, integrating 
an ePTFE vent into the housing equalizes pressure by allowing 
continuous airflow in both directions and preventing the ingress 
of water. What’s more, the vent reduces condensation because 
moisture vapor is able to escape from the luminaire before 
condensing.

* Gary Chan and Henning von Lepel are Application Engineers  

   at W. L. Gore & Associates

Long-term study of pressure differentials  
in electronics housings

Over a period of five years, pressure differentials were recorded  
in five housings.

Long-term study

You will find more information on this topic in the long-term 
study “Life Time Study of GORE

®

 Protective Vents installed  

in Enclosures in Outdoor Environments”, which you can 
download from 

www.gore.com/5-year-study

.

   

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About W. L. Gore & Associates 

Gore is a technology-driven company focused on discovery and product 
innovation. Well known for waterproof, breathable GORE-TEX

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 fabric, 

the company’s portfolio includes everything from high-performance 
fabrics and implantable medical devices to industrial manufacturing 
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where other products fail.

For almost thirty years, Gore has delivered venting solutions for a 
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telecommunication market; mobile electronic devices; and chemical 
and agricultural packaging. Engineered with the latest materials and 
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