Glasshouse films with adjustable light transmittance have the potential
to reduce the high energy cost for greenhouse horticulture operations.
Whether these films compromise the quantity and quality of light
transmission for photosynthesis and crop yield, remains unclear. A
“Smart Glass” film ULR-80 (SG) was applied to a high-tech greenhouse
horticulture facility and two experimental trials were conducted by
growing eggplant () using commercial vertical cultivation and management
practices. SG blocked 85% of ultraviolet (UV), 58% of far-red, and
26% of red light, leading to an overall reduction of 19% in
photosynthetically active radiation (PAR, 380 - 699 nm) and a 25%
reduction in total season fruit yield. There was a 53% (season mean)
reduction in short-wave radiation (385 nm to 2105 nm upward; 295 to 2685
nm downward) that generated a net reduction in heat load and water and
nutrient consumption that improved energy and resource use efficiency.
Eggplant adjusted to the altered SG light environment via decreased
maximum light-saturated photosynthetic rates () and lower xanthophyll
de-epoxidation state. The shift in light characteristics under SG led to
reduced photosynthesis, which may have reduced source (leaf) to sink
(fruit) carbon distribution, increased fruit abortion and decreased
fruit yield, but did not affect nutritional quality. We conclude that SG
increases energy and resource use efficiency, without affecting fruit
quality, but the reduction in photosynthesis and eggplant yield is high.
The solution is to re-engineer the SG to increase penetration of UV and
PAR, while maintaining blockage of glasshouse heat gain.