Light and Lighting

Unfortunately, seeds and cuttings as well as more mature plants are light-dependent, requiring healthy doses of sunlight or well-balanced artificial light. The sunroom or greenhouse may provide for such needs, in colder climates, and be all that is required for a successful start. Glass and plastic transmit all the light necessary for photosynthesis.

Please note that some seeds require dark, not light, in order to germinate. This is noted for the individual plants, if applicable. Intense, scorching sun can also harm seed and seedlings, though protection, i.e. dappled shade, is more easily provided outdoors than trying to rig a proper indoor lighting setup.

During winter, lighting needs of many species decrease. Plants, including cacti and succulents, may often be kept in cool and somewhat darker rooms. Water sparingly in cool, low-light situations.

The spring windowsill, in northern climates, often provides limited hours of low-intensity lighting. Young seedlings crane their heads toward light, quickly becoming straggly. Cacti and succulents, especially those with spines, hairs, or waxy coating, as well as numerous other species, have high light requirements. Here, artificial light can be a definite boon. Hence, the following section.

Artificial light

Balanced light refers to balanced amounts of red and blue light being available to a plant. The former is necessary for stem and root develop-ment, while the latter stimulates solid leaf growth, and thickening of the stem. Seedlings need light, up to 16 hours per day and, as a rough fig-ure, some 20 watts per square foot.

For light-germinating seeds, start light only inches from the soil, and, as plants grow, gradually raise the light source, keeping it some two to three inches above the tallest seedling. Move them outside, or migrate them to the summer windowsill, as conditions warrant.

Ordinary incandescent bulbs produce red light predominantly, and inefficiently. Fluorescents are more efficient, and can provide better quality light. A minimum of two fluorescent lights, side by side, is required. Note that cathode decay causes tube performance to drop gradually over 6 months to a year, and that tubes should be replaced within this timespan, even though they still appear to perform well.

Cool white bulbs peak in the green part of the spectrum but are adequate for good growth; for more of a balance, use a warm white and a cool white bulb together. This provides somewhat more red light, and is more than adequate for almost all species.

Daylight tubes, or better, plant growth fluorescents, offer the best conditions for plant growth, at a higher price. The former produce a more natu-ral white light, and are relatively inexpensive. The latter peak in the blue and red parts of the spectrum, producing a lovely purple glow. Wide spec-trum plant growth tubes are often more pink than purple, and may be more acceptable esthetically. Sylvania, General Electric and Philips all make good tubes, and most should be available locally.

Finally, full spectrum tubes seek to emulate daylight as closely as possi-ble, and are suitable for plant growth. Tubes with a colour temperature of about 5000K simulate equitorial light conditions; a colour temperature of 7500K most resembles the noon sun in temperate areas. Check with your local lighting supplier.

To start most seedlings, an adequate lighting setup consists of two side-by-side fluorescents, on a timer set to provide light for 16 hours per day, though a four-tube fixture is much better. Reflective foil should be used to enclose the seed-growing area, preventing significant amounts of light from being lost to the surrounding area, as well as helping to maintain an adequate humidity in the immediate area.

High Intensity Discharge light

High Intensity Discharge lamps, or HID lamps, can be used to illuminate relatively large areas efficiently. Where winter months normally make plant growth difficult, the growing season can be extended indefinitely. Sizes vary from 70 to 6000 watts; a 1000 watt model will cover an 8 x 8' area with near-daylight intensity, for less than $1 per day.

Metal halide lamps give the best results, though more expensive than mercury vapour lamps. The colour corrected forms, HQI lamps, best reproduce daylight. Mercury vapour lamps have an irregular spectrum con-centrated mainly in the blue, but can still produce good growth, at a cheaper cost. Both forms should be replaced every few years.

Aquarium lighting

There is little role for incandescent lighting in growing plants, and least when dealing with aquaria. Some may even come with incandescent lights, though these do little: to provide enough light to grow plants, you'd produce enough heat to seriously harm, often kill the fish. Light quality is poor, and operating costs are high. Avoid them.

Fluorescents again may be used to good effect, and again, should be changed every six months as their output drops. Cool white tubes, or better, using both a cool white and a warm white bulb provides reasonable light; using plant growth lights in combination with daylight bulbs gives very good light quality for the price. As the depth of the aquarium in-creases beyond 18", increase the number of tubes used to provide light.

Keep in mind the light needs of fish as well as those of the plants to be grown in the aquarium: some require high light levels, best provided by two or more wide-spectrum daylight tubes, in the 7500K range; a plant growth fluorescent may be mixed in though the daylight tubes themselves often suffice for good plant growth. For fish with low light needs, one or two plant fluorescents should suffice.

Tri-phosphor tubes, with sharp spikes in red, green and blue wave-lengths, can be effectively combined with plant growth lights. Typically, a very bright, white light is produced; those with greater amounts of red, i.e. in the 3000 to 4000K colour temperature range, are best for aquarium settings. The Triton variant on these tubes is useful especially in growing anemones and corals, and are interesting in that their light output does not significantly degrade over time, unlike other fluorescents. Generic tri-phosphor tubes are relatively inexpensive; Triton tubes, however, are not.

Some tubes are used in very limited roles, i.e. the actinic tubes that emit light especially in the blue wavelengths, to enhance growth of anemones, corals, and algae; these are useless in growing freshwater aquarium plants. Their price, also, is substantial.

Finally, in some aquarium applications, intense light levels are required. High output fluorescents may sometimes be used, as may HID lamps. Since this takes us well beyond the scope of the average home aquarium, no more is said on this subject, here.

About photosynthesis

This little bit of theory is more for your interest, and can easily be skipped, and/or forgotten. I provide it, however, because of personal interest, and because it provides the scientific rationale for the preceding discussion.

Green plants have the ability to absorb the sun's energy and convert it into a more useable form, specifically, to use this energy for the construction of new plant tissues. Two types of chlorophyll absorb most of this energy, much of it in the red and violet-blue parts of the spectrum. Other pigments, including the famed carotenoids, are absorb solar energy.

As is diagrammed in the Pictures, light energy is extracted from most of the visible spectrum, though green light is absorbed relatively poorly. This is reflected back into the environment, causing plants to appear green. It also shows why both the red and violet-blue parts of the spectrum are im-portant to plant growth. This is the balance referred to at the start of the section on artificial light, the balance that plant growth lights especially attempt to reproduce, and the one we try to approximate using the various combinations that have been suggested above.