Designing a garden is related to the composition and combination of spaces and shapes. It is this intelligent play of assembled volumes that can be perceived by the juxtaposition of shadows and light reflected by the objects of the garden in order to give the human beings the visual perception of the space. As an open space, the garden is always under the influence of lighting, natural or artificial and it is one of the compositional elements to be considered when designing the garden from the beginning phase, in order to conceive a harmonic perception of empty and full spaces. Lighting should be considered in relation to the reaction of all the surfaces that compose the garden and in relation to all the changes that occur in the definition of lit and dark spaces from the day to the night, including the transformation of shadows during the day also caused by the clouds.
In order to control and design the effects of the natural and artificial light on a surface, a space, a volume it is necessary to check the chromatic effects of the materials of the garden, the geometrical shapes, the dimensional characteristics and also the tactile features of the surfaces: as an example a lucid surface will determine a different result from a matt or smooth surface that, will react in a completely different way from a rough and irregular surface. These principles are valid for architectonic volumes but also in a garden with the only difference that we do not have to consider walls and ceiling but just the landscape, a sort of unlimited space with a line of horizon and the sky as a light diffuser and roof. Designing the garden, some physical elements should be taken into account: as an example, materials and the vegetal elements with their consistency, their chromatic hues and also their periodicity (seasonal or evergreen plants). These considerations could be useful to shape the garden thanks also to lighting (both natural and artificial): in order to obtain a visual perception of a wider space, several plants with a white and yellowish inflorescence should be taken in consideration because they are able to better reflect the solar rays.
This yellowish flowers into the green vegetation are able to capture the light in order to reflect it with a radiant effect: the same effect can be achieved with the use of different hues of leaves: the juxtaposition of a darker and matt foliage with a lighter ones create a sort of chiaroscuro effect in the garden. This is an effect obtained in architecture by using different materials together in combination and composition. More than this, colours such as white, light grey and yellow are able to magnify other hues, as for example, the light blue is exalted by lemon yellowish flowers and white details of the garden. Moreover the selection of material should take into account the use of shiny leaves that reflect the light and, in some hours of the day creates real reflective surfaces.
In the chromatic composition of the garden it is mainly important “capturing the light” in order to seduce the spectator, attract the eyes toward a certain element, create several focal and concentration points conditioning the perception and determining a hierarchy between elements and spaces. Moreover the vegetal elements are a natural system to create mutable, dynamic variable shadows that can attract human beings’ attention, restore and relax and create a fresh sensation because they are able to filter the solar rays. The movements of the bushes and the foliages of trees generate a continuously changing atmosphere of shadows and light, thus transforming the perception of the space. The same can be achieved by introducing some water pools in the garden that, reflecting the sky, determine a supplemental source of lighting on the ground.
All the previous consideration are useful not only for the natural lighting but also for the artificial lighting: the main idea is exalting the existent, playing with materials, reflecting light where it is possible, magnifying the light emitted by the artificial lighting fixtures (as well as the natural day lighting) and create a new perception of the urban natural space also during the night. Today the urban garden are useful for ecological reasons, because they are the only place in the city where the nature has a protagonist role, but they are important also for their relaxing and social role of informal meetings and regeneration from the chaotic life. For this reason it is fundamental to guarantee their use also in the darkest hours with safety and security, assuring at the same time a growing oxygen source for the city and a place of intergenerational and multi-ethnical meeting. Lighting should investigate the social role of the garden, influencing the perception of the image of the place, characterizing strongly the mood, inviting people through a scenographic use of the light in an identitary and recognizable space.
More than this, artificial lighting can add a particular ecological meaning for the wellbeing of plants and vegetation of the garden in general: the idea is that lighting can be useful not only to see the garden and to move, orient people around, creating a special lit atmosphere, but can be also beneficial to the well-being of plants. Light can feed the nature, while creating a lit visible scenario for human beings: the relationship between artificial lighting and nature is interpreted not only as staging but also with an attention to the growth of plants. Probably the two most desirable attributes in today’s plant-growing applications are the control of the spectral content of the light and high efficiency (low heat load and low operating cost). The U.S. National Aeronautics and Space Administration (NASA) found in a 2003 Research and Technology brief “a major challenge to growing plants in space controlling and supplying sufficient quantity and quality of light,” using LEDs lighting sources that work where “conventional” lighting fails. “LEDs are a promising electric light source even for space-based plant growth chambers and bioregenerative advanced life support because of their small mass and volume, solid state construction, safety, and longevity,” wrote Duong Tan Nhut and Nguyen Ba Nam of the Vietnam-based Tay Nguyen Institute of Biology in their January 2010 paper.
In addition to being energy efficient and relatively cool, LEDs can provide plants with the proper quality of light, too. “LEDs can illuminate near the peak light absorption regions of chlorophyll while producing virtually no near-infrared radiation (which is not [used] in photosynthesis),” NASA said. The lighting system is basically based on the combination of RWB, a new way to interpret the coloured lighting with a special attention on men and environment. This kind of lighting can assure the best features for the growth and development of plants depending on several scientific parameters that are able to promote the photo-biological processes. The correct development of the plant is obtained when two of the processes of the photosynthesis of the chlorophyll: the respiration of the plant and the photosynthesis.
The photosynthesis is determined by the number of photons (PPFD Photosynthetic Photon Flux Density) comprised in the between 400 and 700 nm that the plant is able to absorb.
The beginning of the visible spectra (380-400 nm) is useful for the beginning of the absorption of the chlorophyll. The range of the spectra between 400 – 520 nm includes purple, blue, green light promotes the vegetative phase of the plants. The absorption of chlorophyll is determined in this moment and influence the photosynthesis. The range of the spectra between 610 – 720 nm includes red light: in this range there is the peak maximum of the absorption of light by the chlorophyll, thus providing the blossoming of the plant.
So, light should be quantified in luminous flux of blue and red lighting in function of the peaks of absorption of the spectra by the plant. Plants in fact convert light from the sun into energy through the process of photosynthesis, but plants only need some parts of the sun’s color spectrum. Blue and red LEDs can provide just the light a plant needs, making the process more efficient and growing a stronger, healthier plant. “The combination of red and blue light proved to be an effective lighting source for growing spinach, radishes, and lettuce. However, the addition of green light may promote increased plant growth since green light penetrates the plant canopy better than red or blue light. Leaves in the lower canopy could use the transmitted green light in photosynthesis.” said the NASA.
Presently, most plant growing is done with blue and red light, but a recently emerging field in horticulture is the discovery that the ideal spectral content, and the ideal timing of both brightness and colors through the day and the seasons, is different for various types of plants. So, whereas most plant growing now uses blue and deep red LEDs, the future ideal horticultural light sources might have any number of tunable wavelengths adjustable to the specific plants being grown. No legacy light source can provide the combination of high efficiency, tunable spectral content, and controllability of LEDs.
This is in many aspects an integrated measuring, planning, dosing and implementing system for the growth of plants.From this point of view the garden could become a urban horticultural land where to grow healthier fruits and vegetables but also plants in half of the time with no pesticides or hormones. LEDs lighting predict this vision for the wellness of plants and human beings.
La luce e il giardino, Illuminare il verde, M. Cristina Tullio, Rivista bimestrale AU Tecnologie, speciale illuminazione, Maggio/Giugno 1991