Reprinted with permission from AmeriLux International eNewsletter (October 2015)
There are many factors to consider when choosing a glazing material for a greenhouse. Factors to weigh are durability, light transmission, ease of installation, insulating qualities, longevity, and cost.
Why is understanding the Yellowing Index important? When used as a glazing material, polycarbonate sheets are exposed to the sun's UV (ultra-violet) rays. The yellowing of a polycarbonate sheet is a visual sign of the degradation of the sheet's surface due to UV exposure.
What is the Yellowing Index? The Yellowing Index (YI) is spectrometric data used to determine the difference in color of a product at any given point in the products life cycle to that of the original product. This can be due to sunlight or an artificial source of light.
The Yellowing Index is measured in terms of "Delta YI". (Delta YI = Change in Yellowness Index.) The YI testing involves a series of comparative measurement and analysis over a given period of time. A Delta YI of <5 is typically not detectable by the human eye.
UV protected polycarbonate versus non-protected polycarbonate. Many advances in polycarbonate technology have occurred over the last few decades. Since the sun's ultra-violet rays are a key factor to panels yellowing, incorporating a high performance UV protective layer will prolong the lifespan of a polycarbonate sheet.
Let's take a closer look at some of the factors listed above:
Durability. Damage caused by UV rays decreases the impact resistance of a polycarbonate sheet. This increases the potential for impact damage. Today's polycarbonate sheets are designed to withstand UV rays and years of abuse.
Light Transmission. The primary purpose of a glazing material is to allow as much light to enter the greenhouse as possible. Light is fundamental to greenhouse production. The loss of light transmission directly impacts the growth of a plant/yield of a crop. Quality polycarbonate sheets will retain their high light transmission values.
Based on light transmission, the LEXAN™ THERMOCLEAR™ 15 sheet has a higher performance value than all other know "like" multiwall products by 2-6 percentage points.
Longevity. A product's warranty will give a good indication of the polycarbonate sheets lifespan and what is covered. Polycarbonate warranties speak to the change in the yellowness over a period of time that the product is exposed to light. Starting from the original color of the material, the warranty will specify how far from the original color the product will yellow over a period of time. The higher the Delta YI, the more yellow the product is from the original color.
With a Delta YI value of 5, the LEXAN™ THERMOCLEAR™ 15 brand will retain its high performance attributes longer than other known "like" multiwall polycarbonate sheet.
Cost. Multiwall polycarbonate sheets contribute to a range of energy reduction strategies, from solar heat and UV control to improved thermal insulation. The lightweight sheets are easy to transport, install, and can be fabricated on site, lowering labor costs. Resins used to make polycarbonate are specially developed with flame retardant properties, translating into lower insurance rates. There may be an initial cost but the high performance characteristics will pay for themselves over time.
LEXAN™ THERMOCLEAR™ 15 has a proprietary UV-protected surface, giving the polycarbonate sheet superior resistance to outdoor weathering. The sheets outstanding weathering performance helps to provide long-term optical quality under intensive sunlight exposure, and maintains the superior toughness of the polycarbonate material in comparison to other multiwall glazing products.
So why is understanding the Yellowing Index Important? Degradation caused by yellowing directly affects the "overall performance" of a polycarbonate sheet. High performance multiwall polycarbonate will not yellow with age and will last for years!