Glasshouse films with adjustable light transmittance and energy‐efficient designs have potential to reduce the high energy cost for greenhouse horticulture operations by up to 80 per cent; however, whether these films compromise the quantity and quality of light transmission for photosynthesis and crop yield remains unclear.

To test this, a group of researchers at Western Sydney University applied ‘Smart Glass’ film, ULR‐80 (SG), to trial eggplant crops in a high‐tech greenhouse horticulture facility, part of WSU’s state-of-the-art National Vegetable Protected Cropping Centre.

Two experimental trials were conducted, growing eggplant (Solanum melongena) using commercial vertical cultivation and management practices.

According to the paper’s authors, ‘the study found that 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 net short‐wave radiation (radiometer range, 385–2,105 nm upward; 295–2,685 nm downward) that generated a net reduction of 8% in heat load and reduced water and nutrient consumption by 18%, leading to improved energy and resource use efficiency’.

Eggplant adjusted to the altered SG light environment with a decrease in maximum light‐saturated photosynthetic rates (Amax) and a 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,’ the paper states.

The research team concluded that ‘SG increases energy and resource use efficiency, without affecting fruit quality, but the reduction in photosynthesis and eggplant yield is high’.

The solution advocated is to re‐engineer the smart glass in a way that increases penetration of UV and PAR while continuing to block heat gain in the glasshouse.