Trial and error is sometimes the best method to find suitable growing locations for plants in the house. Photo: 123rf.com
Light management is one of the main challenges in growing plants indoors.
Plants require light to produce their own food through a process called photosynthesis.
Too little light starves plants of energy, whereas too much light overwhelms them, causing excessive free radicals that damage their cells and can lead to death.
Plants with insufficient light have pale green or yellow leaves owing to low chlorophyll production. They may drop leaves, have spindly stems, or fail to flower. Excessive light can cause scorched, wilted, or flaccid leaves with burned or bleached appearances.
Trial and error is often needed to find suitable growing locations for plants in the house. The rule of thumb is to move under-exposed plants closer to the light source and over-exposed plants farther from the light source.
Low-light plants placed too near windows may sometimes look scorched only on one side of the plant, with the scorched side of the plant directly facing the window.
One reliable way to determine whether a plant can be placed at a certain location is to use a light intensity meter (also known as a lux meter). Such meters are widely available online and, depending on the model, affordable. The light intensity is often expressed as lux (lx) or foot-candle (fc), where 1fc is approximately equal to 10.764lx.
Take several light intensity readings around the indoor garden from 10am to 4pm during the day. Depending on the orientation of the home and nearby obstacles, the period of highest light intensity is not always at noon.
After all measurements are taken, calculate the average. This average of the light intensity readings indicates whether the indoor plants can be placed at the target location.
The University of Georgia has compiled a comprehensive list of about 200 common indoor plants and their light requirements, some of which are presented in the list below.
Level 1 – very high light requirement, with more than 11,000lx, as well as direct exposure to the sun for more than four hours per day.
Level 2: High light requirement between 5,000lx and 11,000lx.
Level 3: Medium light requirement between 2,000lx and 5,000lx.
Level 4: Low light requirement between 800lx and 2,000lx.
Plants with light requirement levels 2 to 4 cannot be directly exposed to the sun, unlike those at level 1.
Advanced gardeners may further consider not only the quantity but also the quality of light, recognising that different plants require varying spectra or “colours” of light for various growth stages.
For example, blue light promotes vegetative growth whereas red light promotes flowering. The range of light that plants use for photosynthesis is 400–700nm, which is often referred to as the photosynthetically active radiation (PAR) range. Some advanced LED lights allow for adjustment of the light spectrum to better suit different growth stages.
Artificial light can be used when natural light is insufficient. Fluorescent lights provide a good spectrum of light for plants, whereas compact fluorescent light (CFLs) is a popular choice for small indoor gardens.
LED lights are highly energy-efficient and long-lasting, and are popular because they produce less heat, reducing the risk of scorching plants. High-Intensity Discharge (HID) lights are often used for larger setups and are extremely bright.
Their types include metal halides (MH) and High-Pressure Sodium (HPS) lights. MH is beneficial for vegetative growth, whereas HPS is beneficial for flowering and fruiting. Incandescent lights are not recommended because they are highly inefficient and emit significant amounts of heat relative to light.
For plants suffering from excessive direct light, light can be diffused, such as by using frosted glass or cloth screens. They scatter light and reduce the intensity without compromising the quality. Plants also use diffused light more effectively than direct light. For plants needing more light, reflective materials, such as aluminium foil or white plastic, can be placed around the plant to amplify light exposure.
Light intensity requirements for some indoor plants
Light level 1
Agave, Aloe, Bougainvillea, Chrysanthemum morifolium, Hibiscus rosa-sinensis (Chinese Hibiscus)
Light level 1 to 2
Ananas comosus (Pineapple), Carissa, Crassula, Dyckia, Echeveria, Euphorbia, Haworthia, Kalanchoe, Opuntia, Oxalis, Pelargonium, Aeschynanthus
Light level 2
Caladium, Coffea arabica (Coffee), Episcia, Fuchsia hybrida (Fuchsias), Hyacinthus orientalis (Hyacinth), Rhododendron hybrids (Azaleas), Tillandsia
Light level 2 to 3
Acorus, Adromischus, Aechmea, Anthurium, Asparagus, Begonia, Billbergia, Brassaia, Calathea, Chlorophytum, Cissus, Crassula, Ficus, Fittonia, Peperomia, Pilea, Plectranthus, Polyscias, Sansevieria parva, Schlumbergera, Spathiphyllum, Tradescantia
Light level 2 to 4
Dracaena, Epipremnum, Philodendron
Light level 3 to 4
Aglaonema, Chamaedorea, Ficus, Philodendron bipennifolium, Zamioculcas zamiifolia (ZZ Plant)
Assoc Prof Dr Christopher Teh Boon Sung heads the Department of Land Management, Faculty of Agriculture, Universiti Putra Malaysia. His field of specialty is in soil and water conservation.
