Optical coatings to increase the yield and quality of protected salads, fruit and ornamental crops


CP 147 - Optical coatings to increase the yield and quality of protected salads, fruit and ornamental crops

Start Date: 
Completion Date: 
Project Leader: 
Dr Simon Pearson, Freiston Associates Ltd
CP 147

Industry representative: James Bean, Crystal Heart Salads Ltd

                                          Mike Opperman, Opperman Plants Ltd

AHDB Horticulture cost: £15,575


Project Summary:

Light is the most fundamental variable affecting plant growth, the light environment can be passively manipulated via the use of optical coatings, or enhanced glass technology. These modifications, whether they manipulate light spectra, light quantity or transmission pattern (diffusion) can have profound and interesting advantages in terms of commercial application. This project seeks to review current and emerging technology used to change light transmission properties of modern glazing patterns. A second phase and project, following the recommendations, may be required to test the materials under experimental conditions.


Project aims and objectives:


 To assess the impact of optical coatings and new glass technology for use in protected horticulture.



The objectives are to investigate the potential of optical coatings for the protected crop industry. These coatings can be considered in numerous forms, including polymer based coatings to glass, changes in glass structural properties to effect an optical change or spray on chemicals to glass (e.g. chalk or other diffusers / reflective materials). The work will be split into two phases, first a desk top review of current technology which will be captured in a detailed report with a succinct grower summary highlighting key information and opportunities for levy payers. This will provide indications of product technical capability and potential applications. The second phase (in a subsequent proposal) will address the questions raised via experimental approaches, and possibly the development of engineering solutions. The second phase will likely involve large scale experimentation and this application relates to funding for the first phase of work involving review and scoping.


A. Review the commercial impact of state of the art and new materials by potential crop response mechanism focusing on applications relevant to current or future UK commercial crop production and including assimilation of the information into outcomes (immediate or via further development) for levy payers, if key questions are not fully answered in the review then knowledge gaps will be stated and identified;


1)         Optically diffuse materials (diffuse glass, polyethylene and spray on materials to glass).

a) Assess the yield gain from optical diffusion

b) Understand the optimum diffusing pattern (isotropic / non-isotropic)

c) Understand the impact on plant growth and stress, especially canopy transpiration patterns.


2)         Solar reflecting materials (e.g. reflective polymer coatings, polyethylene,  spray on coats such as chalk)

a) Understand the benefit from reduced plant stress

b) Understand the potential for improved temperature control and possible yield impact

c) Understand impact of reduced solar gain on greenhouse energy consumption

d) Understand the expected increase in achieved carbon dioxide levels resulting from reduced ventilation attributed to solar control film and its potential impact on yield.


3)         UV absorbing and transmitting materials

a) Understand impact on pesticide degradation, and possible reduced chemical dosages.

b) Identify which specific pests and diseases of relevance to UK production are controlled by UV blocking and assess likely commercial relevance.

c) Assess potential photosynthetic gain from reduced UV photo inhibition.

d) Assess side effects, including impact on bee vision and crop flavour, explore mitigating options.


4)         Far-red reflecting materials

a) Understand the potential impact on plant morphology from far red reflecting materials.

b) Understand the lessons learnt from the use of FR absorbing polyethylene films (Solartrol)



B. Review the commercially available films and recently patented materials



a)         Conduct a review of current and potential new commercially available materials and outline their properties as published by the manufacturers. These include 3M, Saint Gobain, Eastman, AGC Glass, Pilkington, BPI plc, XL Horticulture Ltd, and manufacturers of spray on coatings. Visit the manufacturer as appropriate to understand current marketed product and forthcoming technologies. Establish current uptake of their technologies (e.g. diffude glass or polyethylene, spray on coats). Visit a number of growers who are the early uptakers of these technologies, for example, growers who have installed diffuse glass / polyethylene, gain feedback from real experiences.

b)         Conduct a literature search (including patents) on the manufacturers active in this field, extend the search to include manufacturers of coatings for automotive glass and solar control glass used for heat reduction in building. Most of the ongoing coating development is likely to be conducted for the later two applications. This aspect of the work will be conducted solely for the purpose of horizon scanning. Horticulture frequently applies and exploits materials developed in other sectors of industry.

c)         Irrespective of coatings, understand the technical performance of new glass manufacturing technology (UV opaque and transparent, multiple reflective materials, low iron content glass, tempered glass etc, performance etc)


6)         Potential application mapping. Map the potential benefits of the products currently on the market to horticultural applications. Indicate potential installation costs (if available) and any limitations (warrants, dirt contamination on surfaces, ability to clean glass etc).


Benefits to industry:

The benefits to the industry could be profound: it could produce a significant step forward in the yield potential of all protected crops.


For example, for high wire crops in advanced glass structures, guideline installation costs during a new build of c. £30 m2 may be realistic. The Tomato Growers Association estimate that 1m2 of tomato production creates an income of £55m2. If we estimate that 1m2 of tomato production creates an income of £5.50m2 per year, this would equate to a 6 year payback. We believe the 10% is conservative and would expect the benefit of diffusion per se to approach this level. This generates a positive payback, without quantifyingother benefits in terms of fruit quality, improved environment etc.


There are likely wide scale benefits to the producers of ornamentals crops from diffuse glass, potential post-hearvest and yield benefits for the producers of soft fruits. Impacts of produce colour, flavour and appearance may be significant across a range of sectors.


The project will also provide longer term benefits in developing an improved scientific basis for the design of new materials.