Optimization of the glasshouse environment in summer using the selective infra-red filter material, Luminance THB, as an internal shade screen

The Luminance THB screen reduced the light transmission by approximately 20% when averaged over the duration of the chrysanthemum crop.

The screen significantly reduced ventilation rates, which increased with windspeed, from 25% in calm conditions to 48% for a windspeed of 4 m/s. The effect of this was to increase the average temperature by 0.7°C beneath the Luminance THB screen compared to an unscreened house. On a hot sunny day, the temperature differential excess was 2°C averaged from noon to early evening. The maximum difference recorded was 3.3°C.

Leaf temperatures were affected less by the screen than air temperature. Under high  irradiance conditions, leaf temperatures under the luminance screen were 2°C lower than air temperature, whereas the difference without the screen was about 1°C.
The Luminance THB screen increased the vapour pressure deficits (VPD) during the day due to an increase in air temperature and a reduction in light transmission (which would reduce transpiration, and hence the water released into the environment).

Vegetative growth and flower development generally did not differ significantly when grown under the screen.  The exceptions were reductions in height of up to 7% and a trend towards increased leaf area development under the screen. The former was attributed to possible alterations to the far red ratio or increased daytime VPD under the screen, which could have reduced plant height. The latter, was attributed to the more diffuse light environment under the screen (indicated by the lack of shadows) which was more conducive to leaf area development.

AIM:

To test the effect of Luminance THB, a polyethylene film incorporating a chromophore designed to selectively reduce the transmission of the infra-red component of solar radiation, in summer on the growing environment below the screen.

OBJECTIVES:

• To determine the physical effects of utilising Luminance THB as an internal shade screen on the growing environment below the screen and also on the aerial environment above the screen
• To determine the effect of the internal screen on ventilation rates in order to optimise the potential benefits of using infra-red spectral filters as internal shade screens within glasshouses.
• To determine the effects of using Luminance THB as an internal shade on a growing crop of year-round chrysanthemums.