Artificial Lighting for Orchids: Part One—The Basics!

rtificial lighting is probably one of the most confusing topics for orchid enthusiasts. In our upcoming articles, we will attempt to demystify this somewhat technical subject by first outlining the basic principles of lighting. Subsequent columns will address practical considerations and answer readers’ questions.

The Lighting in Our Homes Is Inadequate, Particularly During Winter Months

In their natural habitat, tropical orchids are exposed to strong sunlight, particularly when they are epiphytes, which means they grow high up in trees. When we try to grow them indoors, they obviously lack light. Not only are the days very short in winter, but light rays are also greatly attenuated when they pass through the glass of our homes. This is particularly the case if our homes have high-energy windows. This type of glazing consists of three panes of glass and is often covered with a ‘low-emissivity film’ that aims to reduce heat loss through thermal emission. This film (known as Low-E film) is partially reflective and it deprives us of precious photons in several wavelengths.

There is less light, and the light spectrum passing through the glass is incomplete, particularly at the extremes of the spectrum. For example, ultraviolet rays and deep reds are almost entirely blocked by the glass. Since these extreme wavelengths are not easily perceived by the human eye, we rarely notice the difference. However, our plants will clearly perceive this deficit in light intensity and spectral quality.

Therefore, photosynthesis slows down due to a lack of light to stimulate the essential chemical reactions for creating carbohydrates. Some less demanding plants, such as those with tender foliage, will not be too affected by this, but tropical flowering plants, such as most orchids, will find it very difficult to complete their annual growth cycle indoors.
In practice, we often have to use artificial lighting to meet the lighting requirements of our tropical orchids, particularly those that are accustomed to intense light in their natural habitat.

Different Wavelengths of Light Have Different Effects on Plants

We all know that white light is made up of different wavelengths, which are the colours of the spectrum. However, few people know that plants absorb these wavelengths very selectively. In particular, red light contains two wavelengths that stimulate plant growth. Conversely, blue light contains two wavelengths that strengthen newly created foliage by giving it more strength.

It was long believed that wavelengths outside the photosynthetic spectrum, such as green, near-infrared, deep blue and ultraviolet, were of little importance for plant growth. However, research in recent decades has shown that all of these wavelengths complement the photosynthetic spectrum and are useful after all. This includes near-infrared (dark red), which is said to have antifungal and antibacterial properties; deep blue; and UVA (near-ultraviolet), which contribute directly to crop hygiene. A study of Phalaenopsis plants found that the cuticle (the transparent layer on the surface of the foliage) was three times thicker in those exposed to light rich in blue and ultraviolet. This tougher cuticle thus provides much better protection for the tender cells underneath.

Some authors claim that certain insects, particularly scale insects, avoid areas of strong light in order to prevent themselves from drying out due to red thermal radiation or becoming blinded by blue and ultraviolet rays. This is certainly true of young scale insect larvae, which are highly sensitive to these rays and can dehydrate quickly when exposed to intense light. This partly explains why scale insect larvae develop deep within the substrate, away from light.

In short, all the wavelengths produced by the sun seem to serve some purpose, whether for the growth of the plant (i.e. photosynthesis), its hygiene, or protection against infection.

Several ‘beneficial’ wavelengths are absent indoors. Glazing only allows visible light to pass through, resulting in a color deficiency that weakens our collections. It is therefore unsurprising that insects and diseases proliferate in our interiors, where certain purification mechanisms are deficient or absent (e.g. UV, blue and extreme red light).

In summary, if you want to grow orchids indoors, you must increase the light supply and try to provide a complete light spectrum to avoid color deficiencies for both photosynthesis and the hygiene of the collections.

Light Intensity Must Be Adapted According to the Species Being Cultivated

Some plants thrive in full sun, some in partial sun and some in shade. The same is true of orchids, whose light requirements vary greatly and are less well known than those of plants traditionally grown indoors. Therefore, you should consult reliable sources written by experts. This step is important because it helps you avoid investing in expensive plants that would not grow well in your home.

To give you an initial idea of the different recommended brightness levels, I have included some photos of typical orchids in different lighting conditions (in ascending order). All photos are from the author.

Paphiopedilum hybrids – Low to moderate light: Paphiopedilum produces spectacular blooms and is undemanding in terms of light. A windowsill is usually sufficient, provided you can find an appropriate window and move it to a different location if necessary, depending on the season.

Phalaenopsis hybrids – Moderate to intermediate lighting: Phalaenopsis is the most popular orchid, but its light requirements are often underestimated. If your window isn’t very bright, you’ll need to provide supplemental lighting.

Oncidium hybrids – Intermediate to bright light: The level of light required by Oncidiums (and related orchids) is rarely achieved on a windowsill, especially if you live north of the fortieth parallel.

Cattleya and Vanda – Strong to very strong lighting: A windowsill will be completely insufficient for Cattleya and Vanda orchids.

Plants Are Real Living Solar Panels!

In short, light is the vital energy source for all plants, including orchids. Remember that it is impossible to compensate for a lack of light through other means, such as fertilization, heat, or watering. Therefore, before growing orchids indoors, you must realistically and critically assess the growing conditions to avoid making significant investments that would only lead to disappointment. In our next article, we will attempt to put these principles into practice.

Editor’s Note

Mr. Charpentier’s orchid articles are published on the Laidback Gardener website under a legal “Copyleft” format. As a result, republication of his columns is permitted provided that the following credit is added: This article was originally published in french on the jardinierparesseux.com website and in the English on laidbackgardener.blog.