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

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.

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Improving existing greenhouse structures in terms of insulation and other features can save energy with significantly lower investment costs than building new greenhouses. Within the EU Framework VI project GREENERGY a decision support system has been developed that offers the potential to be used by the advisory services for growers all over Europe. It evaluates the impacts of either using different greenhouse materials (e.g. for the cover or screens) or building a complete new structure on the overall energy consumption and crop yield. The system is constructed as an easy to use software tool based upon a set of simulation model modules for greenhouse energy fluxes, crop growth and yield. The user defines the structure of his present greenhouse from the pre-defined menu. This greenhouse is then used as reference greenhouse that can be compared to the various modifications of it that the user selects. The entering of additional variables such as geographic location (country), type of crop, internal greenhouse climate set points etc. allow simulations of energy consumption and crop yield over a period of one year using reference climate data of the respective location as input to be performed. The system is constructed in a way such that the database of greenhouse construction materials can be updated easily to maintain its applicability.

An explanatory model for predicting kalanchoe plant height and cropping duration has been developed for one cultivar and one pot size, as described in earlier papers. In two experiments (winter and summer) seven contrasting cultivars ('Anatole', 'Debbie', 'Delia', 'Mie', 'Pandora', 'Tenorio' and 'Toleda') and two pot sizes (7 and 10.5 cm) were analysed to make this model more generally applicable. The studied cultivars showed a strong variation in plant height (10.2 to 29.2 cm) and reaction time (55 to 64 days, from start of short-day period until harvest) when grown under the same conditions (values provided are for summer cultivation in 10.5 cm pots). The effect of pot size on plant height was closely related to the cultivation practices, which already corresponded to model input parameters. For instance, smaller pots resulted in shorter plants but this was due to a lower initial number of internodes and a reduced duration of long-day period. Additionally, growing plants in smaller pots resulted in a longer reaction time especially during winter (on average 8 days delay). The framework of the explanatory model previously developed for 'Anatole' grown in 10.5 cm pots was successfully adapted to other kalanchoe cultivars and pot sizes. It was concluded that when implementing this dynamic model to predict plant height and reaction time for different cultivars in different climate conditions, only few parameters have to be quantified and compared to the reference cultivar at one light and temperature condition.