How to solve the design difficulties of internal and external pressure difference of LED outdoor lighting?

How to deal with pressure difference is still a hidden design difficulty. Moisture-proof and breathable design can enhance the reliability of LED lamps and extend their service life.

　　Many commercial and residential lighting have been upgraded to LED light sources because solid-state lighting (SSL) lamps can continuously deliver more than 100,000 hours of light and are also the most environmentally friendly and reliable lighting solution available today - especially in outdoor lighting. However, outdoor applications are changing and harsh environments, and potential water leaks can cause lamp malfunctions and failures. Although product developers can seal lamps to isolate them from the environment, the overlooked pressure difference between the air inside the lamp and the outside air can cause many problems. Let's explore this pressure issue and consider mechanical design methods to eliminate this problem to ensure the life of the lamp.

　　The benefits of LED lamps are numerous. In addition to the long lifespan mentioned above, solid-state lighting products fully meet Restriction of Hazardous Substances (RoHS) regulations and use up to 85% less energy than traditional lighting technologies.

　　Although LEDs themselves can last for more than 20 years, this life cycle can only add value to the entire lighting system if the accompanying electronics, power supplies and drivers, and the entire lamp are as reliable and durable as the LEDs. All parts of the lamp must be able to withstand the harsh conditions of the environment, whether it is the tropical climate of the Caribbean or the freezing cold of Alaska.

　　Challenges of Harsh Environments According to a study by RTI International, the leading cause of LED lamp failure is driver power problems such as capacitor and interconnect failures, voltage, and moisture or other chemical intrusion.

　　Traditional drivers come with a five-year warranty, but tests have shown that these drivers have a high failure rate. Reliability issues are often caused by seals, joints and connections that are damaged by environmental conditions.

　　Most engineers typically use the following three methods to enhance the durability of the lamp housing to protect the driver and electronic components: use a more durable seal or gasket to improve the seal; increase the housing thickness to reduce the housing movement around the seal; and/or install more screws around the seal or gasket to maintain a longer-lasting seal.

　　However, even with these measures, the seals leaked, allowing water intrusion and eventual condensation to form on the lenses and reflectors.

　　This happens all the time because sealing the entire fixture makes it unable to handle pressure fluctuations, whether positive or negative (or vacuum). When such pressure fluctuations occur, they put great stress on the seal and other connection points, which affects the seal. Over time, the frequent expansion and contraction of the seal can cause the seal to fail at the weak point, thus losing its seal and allowing water, dust and contaminants to enter the fixture, resulting in potential corrosion, short circuits or electronic component failure.

　　Temperature changes, whether external, internal, or both, are one of the most common causes of pressure differentials. External temperature changes can be very dramatic (such as a sudden downpour on a hot summer day) or they can be more gradual as the seasons change. The temperature can drop by as much as 10 to 20°C from day to night each day, and the seasonal temperature difference between winter and summer can reach more than 40°C.

　　When the temperature rises, the air inside the fixture expands, creating positive pressure on seals, joints and connections. When the temperature drops, the air inside contracts and forms a vacuum, again creating pressure on the seals.

　　A 30°C temperature change will cause approximately 10% of the air to flow into or out of the luminaire.

　　For lamps of varying sizes, a rapid drop in external temperature can create a vacuum of 0.5 psi (35 mbar) or more inside the lamp. When a vacuum occurs, water, dust, and contaminants can enter the housing. In the best case, corrosion is accelerated; in severe cases, catastrophic failure can occur. Corrosion can damage the LEDs, wires, cables, and other electronic components contained in the lamp, and ultimately shorten the life of the lamp.