Quality LED fixtures: plastic vs. glass

A major design challenge in achieving high reliability for a LED fixture is how to protect the LEDs from the outside environment. This is especially true in greenhouse environments, where the atmosphere can be very demanding for electronics. The fixture must continue to operate for many years without significant deterioration in light quality. For this reason design choices have to be made, in which the electronics and LEDs are properly protected against this kind of climate in the greenhouse.

Why glass?
The LEDs in the Oreon Grow Light are protected by glass. Lemnis Oreon has evaluated many different cover materials for the delicate LEDs, to find the most durable solution to achieve high light-output over the entire lifetime of the fixture. The requirements for a cover of a LED fixture with a very long lifetime are remarkably similar as the requirements for the cover glass used in the solar panel industry. Solar panel cover glass needs to have low light-losses, be resistant to harsh weather conditions and have to keep working for more than 20 years. The solar industry has matured now and during this learning curve it appeared that some solutions are very well suited for a long lasting LED fixture. After evaluating the other possible materials like PMMA or Plycarbonate, Lemnis Oreon had to conclude that the only option for a truly durable fixture is to use that same technology: Glass.

From a production point of view glass is not the easiest material to use in a light fixture. Thermoplastic materials like PMMA or Polycarbonate are much easier and cheaper, it can be injection molded, can be easily shaped and glued and is lightweight. However, there are several severe disadvantages in using plastics as a cover for LEDs.

What is the difference?

Yellowing: Plastics are prone to yellowing over time, severely degrading the light output of the fixture. Glass will not suffer from this degradation.
Scratching: Scratching is a real problem with plastics, especially when cleaning the light fixtures from accumulated dirt. With the glass cover of the Oreon Grow Light this is no problem. Our waterproof fixture is even easier to clean because a customer can just use a pressure washer to clean the fixture.
Dirt burn-in: It is common for dirt to accumulate on surfaces in a greenhouse. A dust particle or small piece of dirt that has landed on the cover glass will quickly heat up to a temperature high enough to melt or burn a plastic cover. This is no problem with a glass cover, so dirt will not permanently stick to the cover glass.
Permeability: Most plastics allow gases and moisture to slowly diffuse through the material and eventually into the LED compartment. Glass is used in many applications where this is unacceptable, such as medical vials with fluids and the halogen light bulb where the gas has to be contained.

In addition to these benefits of using glass, instead of plastic, the Oreon Grow Light 2.1 uses a type of glass that contains almost no iron, to improve optical clarity. On top of that Lemnis Oreon opted to use a very good antireflective coating on both sides of the glass to drastically reduce reflections: This improves the light-output by another 8%. Below, a few examples of how a plastic cover will last during use in a greenhouse.

Figure 1: close-up of plastic cover after 5 years of use in a greenhouse. Clarity has degraded, dirt has burned into the surface and many scratches can be seen.

Figure 2: close-up of plastic cover of a nearly new fixture of the same type as in figure 1. Clarity is much higher and no dust has burned in yet. Scratches can already be seen.

Figure 3: close-up of the Oreon Grow Light 2.1. Camera is focused on the glass. Except for the faint green reflections of the camera light, the glass is not visible. Compare the reflection of the camera lights to the same reflections seen in figures 1 and 2. The antireflective coating reduces the bright white spot to just a very faint greenish spot.

Conclusion
It will be hard to beat glass in terms of durability. When using glass, no yellowing will appear and no dirt will burn-in, and will therefore ensure the desired light intensity for many years.

For more information:
Lemnis Oreon
Lorentzlaan 6
3401 MX IJsselstein
Netherlands
T: +31 30 760 0660
info@lemnis-oreon.com
www.lemnis-oreon.com