Artificial Lighting for Orchids: Part Four – Take Advantage of Variations in Intensity!

In any lighting installation, there are inevitably variations in intensity, particularly at the sides of shelves where the illumination is significantly lower than in the center. In this column, we will look at the extent to which illumination can vary and how we can exploit these variations to provide the best growing conditions for our orchids.

You Cannot Rely on Your Eyes to Calibrate Artificial Lighting for Plants

Our eyes are not good instruments for measuring light, mainly because of their great capacity for adaptation. Even if the illumination doubles, our eyes will quickly adapt and give us the impression that the intensity has changed only slightly. 

For plants, it’s a different story. Foliage is a solar collector whose photosynthetic activity is directly proportional to light intensity. When light doubles, sugar production will normally double, allowing the plant to grow twice as fast. This increase in efficiency is crucial for the accumulation of reserves essential for flowering. As we explained in a previous article, many orchids grow and flower according to fairly restrictive annual cycles, during which rapid growth is essential for flowering. To achieve this, it is necessary to ensure that the plant’s light energy requirements are adequately met, regardless of its location on the shelf.

The Geometry of the Installation Determines the Extent of Light Variations

To illustrate this phenomenon of intensity variation, we will reexamine the lighting installations presented in previous articles. First, the three-level shelf shown in the photo below, which also indicates the percentage of light present on the sides relative to the maximum in the center. The decrease in illumination is relatively significant. In the case of the demonstration table, the edge effect is comparable even though the light fixture is relatively far from the growing surface. These decreases in intensity are obviously specific to these two particular configurations and the type of light fixtures used. In a different configuration, the decreases in intensity will be more or less significant.

A Few Tips for Setting up Your Growing Spaces

Here are a few tips for setting up your growing spaces:

1. Concentrate plants with high lighting requirements toward the center.

First, concentrate plants that need a lot of light in the center, where the intensity is highest. This will be the ideal location for plants that are growing rapidly and preparing to flower, as photosynthesis will be stimulated to the maximum.

2. On the sides, place plants with lower requirements, such as:

• orchids that have finished flowering;
• plants recovering from repotting or a weakening treatment;
• young seedlings unable to tolerate intense light;
• any recently acquired plants that you want to gradually adapt to your growing environment.

3. To intensify the lighting, plants can be raised

Some more passionate orchid lovers (including yours truly) will not hesitate to straighten drooping leaves to give them better light. This simple operation can greatly improve light capture, especially if the leaf is drooping outward where the light is very weak. Temporary staking (for a few weeks) should restore enough tone to the leaf so that it remains upright permanently without assistance.

4. Many orchids are sympodial, meaning that they grow horizontally, producing new shoots that emerge from the side of the mother plant (see photo).

This type of plant can easily be placed at the edge of a shelf, with the young shoots facing inward, where the lighting is better.

5. As a general rule, we will try to provide the plant with the maximum amount of light it can tolerate, in order to allow it to photosynthesize at full capacity.

This will remain our best guarantee for ensuring the flowering and good health of our collection.

Measuring Light Intensity Can Be Very Useful

Several orchid societies have a small device for measuring light intensity and make it available to their members. This is often the best solution for characterizing your growing facilities without having to invest in a lux meter. It is also possible to use a photographer’s light meter to take a few relative intensity measurements, which will give you a good idea of the variations in light intensity. Since your goal is to obtain comparative measurements, any unit of measurement will do.

The Simplified Method

Readers who have access to a measuring device can find some tips on how to characterize their growing space by measuring it using the simplified method we suggest:

1. Measure the maximum light intensity at the center of the growing space, keeping the sensor at mid-height of the foliage (see photo);

2. Repeat the measurement on the sides to estimate the loss of brightness (always keeping the sensor at the height of the middle foliage).
3. also measure the maximum intensity at the center of the shelf near the source, approximately 5 cm away from the lights. This measurement will give you an idea of the maximum intensity available in your installation. This information can be very useful for diagnosing excess light on the tips of leaves that come close to it;

4. Record your measurement results in a notebook or directly on the shelf as shown in the photo below. This will allow you to refer to them in the future.

Next Column: Best Horticultural Practices

In our next column on artificial lighting, we will discuss best horticultural practices to maximize our chances of success. Many readers will discover a “surprising revelation” about the importance of good darkness at night!

Feel free to submit your questions in the comments section. If necessary, we will add one or two additional columns to answer them.