Guide to Plant Lighting

Is it possible for a plant to get too much light? In short, yes. Too much light can affect the plant in a way known as “photo-inhibition.”  This occurs when too many photons hit the leaf and reduce photosynthesis.  The most common side-effect of this is bleaching and mottling of the upper growth.

So, how much light do plants need?

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Young plants don’t need as much light as older plants. Seedlings can be grown successfully with low-level natural light or artificial light. Shortly after seedlings have germinated, or even before the first true leaf is visible, the plant starts reacting to the levels of light. If a seedling is not getting sufficient light, cells in the plant stem will elongate, pushing the cotyledons and the developing first true leaf up to seek more light. As a result, a thin-stemmed, weak plant is produced. If the plant survives, the stem will never thicken to equal the normal size at the base of the plant. If there is enough light, this does not happen.

As plants grow and the number of leaves increases, the need for light increases as well. Partially as a result of the newer leaves on the plant shading the older leaves at the lower levels. Providing higher light intensity as the plant grows ensures that more light will reach some of the older leaves on the plant.

What type of artificial lighting is best?

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High-pressure sodium light produces light mainly in the yellow and red end of the light spectrum. Much of this light is usable for plant photosynthesis. However, other processes in the plant, including the control of cell elongation to seek light, react to the presence of light in the blue end of the visible light spectrum. High-pressure sodium lights can be used in a greenhouse to extend the daytime light for plants that are already receiving natural light to keep them growing normally. High-pressure sodium lights are more efficient at converting electricity to light energy than metal halide lights are.

Metal halide lights produce a more desirable light spectrum than high-pressure sodium lights do. If there is no natural light in your setting, you would need to use metal halide lights so that the plants can get the range of light they need to photosynthesize, grow, and develop properly.

Effects of poor lighting

Lack of light

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Symptoms

  • New shoots are weak looking.
  • Slow growth.
  • Small and pale new leaves.
  • Yellow or fallen older leaves.
  • Brightly colored leaves turn green.
  • Plant fails to bloom.
  • Stems are lanky and spindly.

  • The distance between leaves, where they’re attached to the stems, is especially wide.

  • You see fewer flower buds and, thus, fewer flowers.

  • The entire plant leans toward the light sources.

Solution

  • Increase artificial or natural lighting immediately.
  • Reduce room temperature by about 5°F (3°C).
  • Water less frequently and do not fertilize.

Too much light

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Symptoms

  • Leaves exposed to direct sunlight turn pale and develop faded spots that turn dry and brown.
  • Affected leaves turn increasingly pale.
  • Flower petals dry out.

  • Leaf edges look burnt or dried.

  • Flower color looks faded or washed out.

  • The entire plant starts to weaken and droop.

Solution

  • Remove the plant from direct sunlight in summer or filter direct light.
  • Remove badly damaged leaves.

 

Heat burn from artificial lights

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Some lights, like incandescent, fluorescent, and HID lights have bulbs that get very hot. Usually, the heat will burn your crop, and cause tissue death and crop loss. These lights basically cook your plants, especially if they are close to the plant like in a compact or high-density system. It is important to properly cool and ventilate your growing area to avoid these losses. Using cool tubes and ventilators, and fans that you can buy in places like Oasis Garden Hydroponics will fix this issue.

Scorching Factors

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These are some factors that can potentially cause leaf-tip burn:

Watering issues: Leaf scorching can be a sign of erratic or insufficient watering or low humidity. It is especially true for tropical plants, which dislike the dry conditions. The solution is to raise the humidity—mist the plants, use a pebble tray, or relocate the plant to an area with higher humidity such as the kitchen or bathroom.  Finally, make sure the pH of your water is neutral or slightly acidic.

Fertilizer issues: Salts from water soluble fertilizers can cause leaf scorching, especially when large amounts of fertilizer are applied. If you notice scorching on your plants shortly after feeding, the issue might be with your fertilizer. Flush the soil with clean water several times to remove accumulated fertilizer salts and be more careful in the future.

Cold damage: Many houseplants aren’t adapt to cold temperatures or drafty conditions. Cold damage often shows up in the extremities first (the leaf margins and leaf tips). If this happens, try raising the temperature (and humidity) around them.

Sun damage: Sun damage usually shows up as yellowing of the whole leaf, or even scorched spots on the leaves. Move the plant to a shady spot to reduce the amount of sunlight and prevent further burning.

Chemical damage: Household pesticides and cleaning chemicals can burn plants in some cases, so be aware of what you’re using on of around your plants.

Natural Lighting

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 Some rooms in your house will be sunnier than others, depending on which way the windows face. Keep this in mind when selecting a spot for each plant, to ensure that it will grow properly.

South-facing

Plants receive direct sunlight all day long. This is the ideal spot for species that thrive in full sun. Plants that require bright light should be protected from direct sunlight between 10 a.m. and 5 p.m. in summer, however. A south-facing exposure is not a good place for plants that require little light, especially from April to October.

East-facing

Plants receive direct sunlight in the morning and plenty of indirect light the rest of the day. Plants that thrive in bright light will do well in this setting year-round. Plants that require indirect light should be moved slightly back from the window in summer.

West-facing

Plants receive direct sunlight in the late afternoon and plenty of indirect light in the morning. The sun is stronger and warmer here than in east-facing windows. This is a good spot for plants that tolerate a few hours’ sun a day.

North-facing

Plants receive plenty of indirect light in summer, but less light from November to February. Plants that prefer indirect light will do well here year-round. Some plants that require bright light may adapt to this spot in summer.

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