How does the moisture get in there anyway?
Moisture, which is what induces condensation to form, can be added to the air inside the headlamp via three different transfer mechanisms:
- Water vapor sorption of plastic components and housing material,
- Water vapor permeation through plastic housing and lens material,
- Convective and diffusive moisture transfer through venting system
Why are LED lamps particularly vulnerable to condensation?
Condensation in automotive exterior lamps occurs when the lens temperature drops below the internal lamp dew point. LED technologies, which change the thermodynamic conditions inside the lamps, further increase the risk of condensation formation, because:
- LED lamps emit less heat (which would help to dry the lens) than conventional lamp technologies.
- In LED lamps, the heat sources are located at the back of the lamp, so less heat is directed towards the lens resulting in colder lens temperatures.
Typically the heat from LED lamps is just not sufficient to heat/evaporate the condensation that forms and clouds lenses. Two other trends in lamp design further increase the incidence of condensation:
- Newer lamps contain more electronic components, with a corresponding increase in the amount of plastics…further increasing the amount of water released during heat-up.
- As lamp designs become more complex, the open path between the front and back vents of the enclosure is restricted, further restricting moisture diffusion that might otherwise help to counteract condensation.
Can’t existing technologies solve these problems?
Not completely. All the traditional solutions are partially effective, to a greater or lesser degree, depending mostly upon random variables like ambient temperatures and pressures, operating/environmental conditions, and whether the vehicle is moving or stationary. For example:
- Convective systems (rubber tubes/caps with labyrinths or open-cell foam, or cap vents with non-woven material) provide almost no diffusive moisture transfer, and provide minimal-to-no protection against dust and water ingress. Most critically, convective systems only function when a vehicle is moving. (As the typical car is stationary more than 96% of the time, convective systems just can’t provide sustainable lens clearing.)
- Diffusive systems that feature ePTFE membrane vents — a robust solution for many applications — continuously equalize pressure, and prevent ingress of dirt and water. Membrane vents also transfer moisture (via diffusion) from the lamp enclosure, whether the car is moving or stationary. However, diffusion is a passive process that is dependent on ambient conditions and the conditions inside the lamp.
- Anti-fog coatings don’t remove any moisture – they change the interior lens surface energy so the condensation “sheets” instead of staying in droplets. Such coatings limits lens design options. And they have a limited lifetime, after which water drops will form, creating spots and streaks inside the lens.
- Non-regenerable desiccant bags are sometimes put into in lamps, or lamp-packaging, to protect against moisture during transit and storage. Depending on the amount of desiccant and the relative humidity, these bags may function for a few weeks or months, until they become saturated. At that point, they cease to function.
- Fans (that blow hot air from the heat sink to the lens) will dry the lens faster, but will not do anything to reduce the dew point or moisture within the headlamp enclosure.
As this overview demonstrates, the effectiveness of all of these existing approaches is still subject to the interplay of the ambient conditions inside the lamp, with the ambient conditions in the external environment.
If all these approaches have drawbacks, what’s the solution?
First and foremost, to make what happens inside the headlamp enclosure more independent of what’s happening in the external environment. And, for the first time, there is a new technology that can address this challenge.
Now, a technology collaboration between AML Systems and W.L. Gore takes headlamp protection to a new level, with an innovative product that actively prevents condensation:
Introducing AML’s Condensation Management Device (CMD)
enabled by GORE Condensation Management Products.
The CMD uses a combination of electrical power and a regenerative desiccant to actively remove moisture from inside the headlamp, lowering the internal lamp dew point so rapid drops in lens temperature do not result in condensation. Even in extremely humid weather, the CMD actively removes humidity and moisture from headlamps, while providing dust- and water-ingress protection, and pressure equalization.