Selection and analysis of LED microporous material protection and vent design considerations

In this paper, Jason Chen, Maciej Slotwimdki and Gerry Dibattista through the selection of materials and application procedures, provide guidance for designers and users, so that LED can achieve powerful solid-state lighting in wet conditions.

LED itself is a reliable source, for application of water and other hazards, solid-state lighting (SSL) is a very attractive option, its durability also increases the energy efficiency advantage. Ideally, will be exposed to moisture, dust or dirt in the environment of LED products were sealed, to avoid damage to the internal electronic components. However, sealing products may lead to the shell or seal failure, the reason is LED and its driver generates heat caused by internal pressure build-up. A hydrophobic microporous vent, the dust and liquid discharged from the housing, and reduce the housing pressure or negative pressure to protect products. This is a simple and efficient way.

May need to vent the solid-state lighting applications range from outdoor to indoor. In the outdoors, must withstand natural factors; in the indoor working environment will bring risks. For example, figure 1 shows a LED road lamps, it will suffer from heavy rain and other weather, may cause water to enter. In the interior, such as food service applications, solid-state lighting will need to vent, where will the use of pressure cleaning. In addition, any application must withstand the temperature cycle may require lamps with vent hole.

Figure 1. outdoor LED lamps should be used to vent, prevent the lens of fog, to prevent water damage inside the electronic equipment.

The vent can keep moisture out, avoid condensation, to balance the pressure. Ironically, a lamp vent can prove the design completely sealed enclosure more reliably in harsh environments.

porous material

We first discuss the choice of some materials in the design of vent LED lamps. Polytetrafluoroethylene (PTFE) because of its natural hydrophobicity, chemical resistance, heat resistance and UV stability (UV) are usually used in this kind of vent protection. PTFE protection vent by sintering porous membrane or the so-called extension or expansion of PTFE PTFE (ePTFE) (Figure 2) a. Substitute sintering usually better sintering material can withstand mechanical fatigue, usually stronger, and can meet the requirements of UL flammability.

Figure 2. left shows the sintered porous membrane, displayed on the right is the extension or expansion of PTFE. PTFE mechanical strength is lower than the extension of sintered film, shape and aperture less.

Polyethylene (PE) plug or disk is a low cost option to protect the exhaust hole. However, the working temperature limit of PE disk is low, and usually waterproof anti dust is weaker than PTFE. PTFE and PE exhaust hole can be made into sheets, customizable size or three-dimensional shape.

LED lighting

Now, we'll discuss a potential application, a deeper understanding of why reliable operation need to vent lamps. Non vent design may suffer catastrophic failure even temporarily. For example, outdoor LED lamps is one of application. For example, due to intrusion of moisture or condensation, temperature change of the lighting within the housing could lead to failure. The water will enter the lamp lens caused by atomization, will affect the light output, and there will be at least temporarily the functions of failure. The positive and negative pressure may damage the seal around the shell or joints, even if the gasket design does not guarantee in use due to temperature, humidity and mechanical shock does not appear volatility based on the best.

The temperature change may be the natural cycle of the lamp operation results, it may be due to the external environment. According to various conditions, the change of temperature could be as high as 85 ~ C. Even assuming that the temperature is only 15 degrees C, the sealed housing will have about 56 mbar and the external atmospheric pressure difference (0.8 psi). Because of this pressure more than 35-40 mbar, so the protection of LED electronic components and sealing gasket materials may leak, moisture or dust will invade.

IP

The development of new products of lamps developers should exhaust vents as one of the first steps of design. The product team should choose a material exhaust and the implementation way, to satisfy the application flow, fluid invasion resistance and mechanical requirements. Porous exhaust hole, such as viscosity, disc plug or spiral hole vents allow air flow, while continuously lamp protection against rain and other liquids even though air holes can release the air pressure and the water condensation minimized inside the lamp, but the exhaust hole liquid ability to keep water in the shell is important.

Film performance and hierarchy

Vent specifications by the application and entrance door according to the requirements of IEC standard 60529 (IP) of the decision. IP grade refers to the product robustness to damp and dust. Any housing or lamps should have a IP rating, the classification of design according to the application demand. Figure 3. summarizes the IP code.

Figure 3. shows the protection scope of protection.

With the increase of IP number to the IP66 environment, the challenge becomes even more difficult. In general, if the product conforms to the specific IP level, such as the IP65, it will resist the invasion of pollutants and the liquid in the lower level of the. The related IP and liquid level, IPx7 and IPx8 said the water level, they may not be more difficult than by IPx5 or IPx6, IPx5 or IPx6 grade must resist direct high pressure water jet.

In order to match the application procedures and materials, summarized in Figure 3 may be used for different types of materials, the typical porous vent IP grade. The porous membrane material with appropriate waterproof performance can ensure that no liquid and pollutants