The use of LEDs can be promising for greenhouse horticulture, but before it can be put into practice on a large scale more knowledge must be acquired on effects of LED lighting on crops. Furthermore, the growers will have to learn to grow their crops under LEDs and the efficiency of LEDs must increase even more. In order to gain more insight into the influence of LEDs on crop growth and production, an experiment was performed in the Wageningen UR greenhouses with a small Santa type tomato ( Differences in production were small, although the production under all LEDs was lower. There were only small differences in fruit quality. The amount of energy required per kilogram tomato was highest in the LED treatment and hybrid with top LED lighting. This was primarily due to the fact that a higher air temperature was necessary and these LEDs were cooled and the cost of cooling added to the use of energy. The consequences and future perspectives of the different types of supplementary lighting for crop growth and production as well as for crop management practices will be discussed. INTRODUCTIONThe use of LED assimilation lighting can become an important player in greenhouse horticulture if energy efficient LEDs can increase production in the winter. However, before LEDs can be broadly applied in horticulture, more knowledge is necessary on the effects of LEDs on crops, how to manage crops growing under LEDs and how efficient they really are, not only in terms of light output, but also in relation to crop production. While the energy efficiency of LEDs is the result of technical improvement, knowledge on the effects of various lighting systems with LEDs on greenhouse crops and crop management as well as the efficiency of LED lighting per unit production must result from experimental research. To date, in experiments with LED lighting systems in greenhouses problems with crop growth and physiology have been encountered and are thought to be due to insufficient tuning of crop cultivation to assimilation lighting with LEDs (Nederhoff et al., 2010). These problems seem to focus on plant temperature, plant load and the influence of LED lighting on plant morphology

Reliable and quick assessment of energy conservation measures in greenhouse cultivation supports growers in their operations. Such an overview should quantify the consequences of changes in energy flows for total energy consumption, amount and quality of production, and farm economy.Using tomato as an example crop, comprehensive energy balances were developed for a reference situation in The Netherlands. Solar radiation, primary and secondary heating circuits and CO 2 from the flue gasses of the heating system were quantified as energy sources. Energy use for air and leaf temperature increase, crop photosynthesis, crop transpiration, as well as energy losses through the roof, walls and ground surface were quantified. Subsequently, the effects of 11 energy conservation measures were computed. Consequences for gas consumption and production were simulated with a greenhouse and a crop growth model, respectively, consequences for quality were assessed on the basis of expert knowledge, and economic consequences were simulated with a cost-benefit model.For tomato, most energy was saved by increased insulation of the greenhouse cover (23% saving) and lowered temperature set point (16%), followed by increased set point for air relative humidity, screen gap control in steps, and temperature integration (all about 5%). Fresh tomato production fell in most cases, except in case of increased light transmission by the greenhouse cover. Energy use efficiency was defined as the amount of energy required to produce a certain quantity of fresh harvestable product. Energy-conservation aims to decrease the energy use efficiency. Greatest gains were reached through insulation (-20%), lowered temperature set point (-12%) and improved light transmission (-8%). Improved light transmission resulted in the strongest increase of the balance of yield and costs (€2.6, or 10%), followed by increase of RH set point, crop-based RH control, crop-based use of the energy screen, increased size of the thermal storage tank and reduction of crop transpiration (all less than €0.5).Although energy conservation reduces fuel costs, its implementation depends on the effects on production an overall economic profitability of the farm. Improved roof insulation, reduced temperature set point, screen gap control in steps, increase of the RH set point, temperature integration, and crop-based RH control are first candidates for (further) implementation. Other measures require prior technological advancements or fine-tuning. INTRODUCTIONGiven the high costs of energy and obligations imposed on national governments by the Kyoto protocol (UNFCCC, 1997), energy conservation in horticulture has become increasingly important. Reliable and quick assessment of measures to conserve energy supports growers in their operations, and policy makers in directing research funds. Energy conservation assessments require an overview of the most important energy flows and their consequences. Changes in energy flows may have consequences for the

There is a great deal of interest for diffuse glass in Dutch horticulture ever since higher light transmission values and the diffusing characteristics of diffuse glass have increased production for some crops. Thus an experiment was designed to examine the effects of a variation in haze factors and light transmissions for diffuse glass or a diffuse coating on the growth and production of tomato. The influence of diffuse glass with a haze factor of 45, 62 and 71% and light transmission equal to or greater than that of standard glass, as well as standard glass with a commercial coating with a haze factor of 50% and 6% less light transmission than that of standard glass was compared to that of standard glass. The crops were planted midDecember 2010 and grown to the middle of November 2011. The influence of diffuse light on light interception, crop morphology, photosynthesis and growth was measured and analysed. Light penetrated deeper into the crop resulting in a higher photosynthetic capacity in the lower canopy, but only in winter. Tomato grown under diffuse glass was more generative, transferring more into fruit production than vegetative growth, in comparison to standard glass or coated glass. The production under the three diffuse glass coverings showed a 7-9% increase in June relative to that under standard glass, and retained this increased production to the end of the year, ending with 8-11% more production. The most important reason for the increased production was an increase in individual fruit weight by 5-8 g. Plants grown under diffuse glass or coating were less susceptible to Botrytis spp. during the last months of the crop, possibly due to a higher dry matter content. The coating was applied in the beginning of May and the treatment continued through August when the global radiation diminished and more light was necessary in the crop and the coating was removed. The overall production under the coating was 5% higher than that under standard glass. An estimation of the benefits and consequences of diffuse light characteristics on the growth, development and production of tomato under Dutch conditions are discussed, along with recommendations for the optimal characteristics for diffuse glass.

Wageningen UR investigated the potential of several NIR-filtering methods to be applied in horticulture. In this paper the analysis of the optical properties of available NIR-filtering materials is given including a calculation method to quantify the energy reduction under these materials and to estimate the contribution for greenhouse cooling. It can be concluded that the optimum NIR-filtering material is still not found but there is good potential for further developments. NIR-filtering multilayer coatings applied to plastic film or glass filter out NIR most effectively. NIR-filtering is not desirable during winter-time in most climatic regions. Therefore, NIR-filtering coverings should not be used in unheated greenhouses since they cause an undesirable temperature drop. NIR-filtering white washes still reduce PAR too much. NIR-filtering (moveable) screens could be an alternative in the future. Future studies should also investigate whether it is possible to use the reflected NIR energy for other processes or cost-effectively storage.

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Greenhouses have been extremely successful in providing abundant, cheap and high-quality produce, by using resources (water, minerals, pesticides) with a very high economic efficiency. Marginal agricultural land is being rapidly converted into protected cultivation in many (semi-arid) regions of the world, hoping to prosper both from primary and secondary activities. Water use efficiency of greenhouse production is about five times as high as field production of vegetables. However, in spite of using resources more efficiently, greenhouse areas have an enormous visual and environmental impact: diversion of limited good water resources; contamination due to pollutants released with over-abundant irrigation; production of plastic and mineral waste and biological by-products; contamination due to plant protection chemicals and emission of "greenhouse" gases (CO 2 ) by heating with fossil fuels in Northern countries. In addition, greenhouse production has an "image" problem: there is a general perception among European consumers that such an "industrial" production of food is non-natural and unhealthy, although in the Americas, for instance, the "cleanliness" of the production process is considered an advantage. Since, the "polluter pays" very seldom, environment-friendly production is more expensive. Therefore a large market in "eco-labels" has developed in response to consumers' misgivings and in the hope of recovering (part of) the costs through higher prices. However, there is little clarity about agricultural practices associated to each label and there are doubts about enforcement. This paper analyses advantages and draw-backs of greenhouse production, and attempts to review the items where improvement is necessary in order to ensure that greenhouse production is sustainable, yet profitable also in the future. INTRODUCTIONConsumers in developed countries are so used to get appealing, clean looking and cheap vegetables the whole year round, that very few of them are aware that such a luxury was unthinkable just 20 years ago. This abundance is most commonly generated under shelters (protected cultivation) that, for a large fraction of the year, ensure growing conditions much better suited for crop production than open field. This is not new: the advantages of ambient modification in this respect were certainly known in ancient Rome, as Plinius (77A.D.) maintained that the emperor Tiberius could eat year-round cucumbers from plants that were withdrawn under semi-transparent shelters whenever conditions were unfavourable. Similarly, orangeries (buildings devoted to create growing conditions of citrus where citrus would not grow) have been built in the gardens of rich people for many centuries. What is new of the last 20 years is that year-round abundance is so cheap as to be taken for granted. This has been caused by the large-scale application of horticulture under plastic that has transformed formerly marginal agricultural land into a highly efficient and profitable crop production. The most striking exa...

More than 90% of the Dutch greenhouse area is covered with single glass. Energy losses through the covering are high during the heating period (winter) but energy requirements are also high during the cooling period (summer) in the case of semi-closed greenhouses. Until now, light losses of insulating coverings prevented growers from using double glass or plastic film. However, increasing energy prices allow new developments. Wageningen UR Greenhouse Horticulture studied the possibilities to use modern glass coatings to increase light transmission and save energy. Several glass types (standard glass, 90+ glass, low-iron glass) were covered with different anti-reflection coatings from different producers. Double glasses were produced; their optical properties were determined. It was possible to produce double glasses with new coatings having a higher light transmission than traditional single greenhouse glass (83-85% for hemispherical (diffuse) light, compared to 82-83% for traditional single glass) and a k-value of 3.6 W m INTRODUCTIONWith increasing energy prices the need for energy saving is high in horticulture. The energy saving potential of double layered covering materials for greenhouse applications have been pointed out in many research studies before (e.g., Zhang et al., 1996; Andersson and Nielsen, 2000; Bot, 2001; Villeneuve et al., 2005). However, until now suitable greenhouse covering materials combining both a high transmission and a high insulation value for greenhouse applications are missing. Though many studies focussed on the development of modern materials in order to save energy and/or achieve a better cooling of greenhouses (e.g., Swinkels et al., 2001; Waaijenberg et al., 2004; Hemming et al., 2006 Hemming et al., , 2007, the optimum combination of materials' properties is still not found. Since more than 90% of the Dutch greenhouse area is covered with single glass, energy losses through the covering are high during the heating period (winter) but also during the cooling period (summer) in semi-closed greenhouses. This research will show the future potentials of recently developed glass coatings (anti-reflection and lowemission) for single and double materials in order to have a high crop production as well

In general, the use of energy screens is a good means to reduce the energy consumption and to lower peaks in energy use in greenhouse horticulture. In tomato, experience with screens is limited since the use of screens is not so widespread as in other fruit vegetable crops. In this study effects of different screen opening strategies on greenhouse climate, energy consumption and crop production were quantified by means of an experiment and model calculations. In the experiment, two treatments were compared, i.e. opening the energy screen (SLS 10 Ultra plus) at 5 or at 50 W m -2 outside global radiation. Plant dry weights and tomato production did not differ between the treatments. Due to the larger number of screening hours, energy consumption in the 50 W m -2 treatment was 3.5% lower during the experiment than when screens were opened at 5 W m . Financial considerations between energy saving and production loss were discussed. Screen opening based on a combination of global radiation and outside air temperature reduced the energy use, but increased the number of hours with high humidities. Screen opening based on the temperature difference below and above the screen performed comparable to the temperature and light strategy. Opening the screen caused a temporarily decrease in greenhouse air temperature. Increasing the number of opening steps before the screen was opened completely, decreased this temperature drop.This study provides growers with information to determine their screening strategy. However, screen use could be further optimized by offering growers a decision support tool that, given outside weather conditions and prices of gas and tomatoes, gives daily advice on the optimal moment of screen opening.