PREFACE

High supplementary light levels have been applied already for many years by plant propagators and low levels for controlling photoperiodism. The scale, however, on which high level supplementary light was used in most countries was small, mainly due to the high electricity costs. Especially to increase winter quality and winter production of horticultural products, high level supplementary lighting has become a topic in North-Western Europe and North America. In Europe, the rapid development of heat/power co-generating machines (Total Energy) of a size suitable for nurseries of one ha and more, was a strong stimulus. It gave the growers the possibility to produce in addition to heat, also electricity at acceptable costs. By selling the surplus electricity to the grid, these systems became profitable for more and more growers, especially in the floricultural sector. The rose growers belonged to the first who saw the possibility to increase both winter production and winter quality by applying supplementary lighting, and they stepped in on a large scale. They were accompanied by others, pot plant growers and plant propagators. Also the development of high efficiency lamps and better luminairs stimulated the use of supplementary lighting. Besides the use of light for assimilation purposes, artificial light has also been used for dozens of years already for day length control in the cultivation of daylength sensitive plants, e.g. chrysanthemums.

At the symposium the recent developments in research and in practice were presented and discussed. During excursions several practical nurseries with co-generation were visited as well as some research institutes in Wageningen. One evening the sponsors of the symposium was given the opportunity to man their self explaining presentations and to show their products.

The symposium was set up in such a way that many discussions could take place, either in discussion groups, at poster sessions, during excursions and last but not least at informal meetings. To stimulate discussions, posters and the self explaining presentations of the sponsors could be attended during all symposium days.

The first sessions of the symposium dealt with the physiological aspects and crop responses to supplementary light. Physiological background, growth, production and quality were discussed.

The second sessions dealt with light quality and photoperiodism. Different lamp types were discussed, the role of photoreceptors and endogenous rhythms, the effects of the Red/Far-red ratio and the effect of different light qualities (colours).

The third session dealt with technical aspects and energy and models.

Unfortunately the invited speaker Prof. Dr. H.J. Tantau from Germany could not be with us due to a sudden illness. His lecture, however, is published in this Acta. At the last minute, Prof. Dr. Ir. G.P.A. Bot from the Agricultural University of Wageningen, was so kind to ‘fill the gap’ and give a lecture on the subject: ‘Light transmission of greenhouses. Calculations and measurements’.

During one evening a workshop was held on ‘Light Measurement’. After an introduction of Dr. K. Schurer from Wageningen, in which he discussed some common instruments for the measurement of PPF, energy flux and light, a vivid discussion was held about the subject.

Thanks to the financial contribution of the sponsors, symposium costs could be kept at a reasonable level.

The day after the symposium a visit was organised to the Dutch Technical Horticultural Fair (NTV) in Amsterdam. Beside all conceivable technical equipment for horticulture, the members could also see the hard- and software involved in supplementary lighting and make contact with many international manufacturers, suppliers and tradesmen.

G.A. van den Berg
Convener


FOREWORD BY THE PUBLISHER

As an International Society for Horticultural Science, it is our aim to provide the scientific community with an accurate and up-to-date information on scientific results in the field of horticultural research.

It is therefor our wish to publish as soon as possible upon termination of the symposia, the proceedings of the meetings organized under the aegis of ISHS.

Due to reasons beyond the control of ISHS, the proceedings compiled in this number of Acta Horticulturae, suffered a serious delay in publication.

It is thanks to the continuous efforts of several of the participants that this work could be finalized at a moment that we gave up all hope on publication. We wish to thank these persons caring for ISHS for their appreciated collaboration.

Leuven, December 1997