Indoor Grow Light Basic Overview

By the urban gardener

Australia's online hydroponics supplies & indoor grow shop

A grow light, which is, actually, an ordinary electric lamp, is of vital importance for the plants, since it ensures the process of photosynthesis by radiating electromagnetic spectrum, which resembles sunlight. Thus, using grow light, a gardener creates outdoor-like conditions inside the house. However, sunlight is bluish, as it has high color temperature, therefore, rendering index is usually used to check whether grow light is closely similar to the sunshine.  

What Light Spectrum Is Best For Plants

Light spectrum, required by plants, depends on the stage of the plants growth. For example, vegetative stage needs blue light spectrum; while the stage of plants blooming requires red–orange spectrum. A gardener can buy a specific light spectrum bulb, or there are also universal full spectrum lights suitable for different growth stages (for example, those made by Sylvania Grolux).  

To give optimal results the light should be supplied with a reflector and an electrical ballast to regulate and augment light emissions and current. This is done in order to make artificial light as much as possible similar to the natural daylight.

Types of Growing Lamps

High pressure sodium (HPS/SON) and metal halide (MH) lamps are nowadays the most popular and frequently used ones in the professional indoor gardening. They belong to high-intensity discharge lights. Metal halide lamps are mostly used for the initial (vegetative) stage of plants growth, as they emit bluish light along with ultraviolet radiation, which results in the increased production of plants elements, thus improving and strengthening them.

Reproductive or flowering stage of plants growth requires the use of high pressure sodium lamps, since they hasten the growth rate. They are not suitable for the vegetative stage as this would result in the fast growing of too tall plants. Nevertheless, both types of bulbs are sometimes used by the gardeners for various plants growth stages with the additional reddish spectrum adjusted to the metal halide bulbs and bluish spectrum attached to the high pressure sodium lamps

Incandescent Grow Lamps

Incandescent grow lamps are used only to emphasize and highlight plants groups grown inside, as they have red-yellowish spectrum and low color temperature (about 2700°K). They are never used as the grow lights. The life span of incandescent growing lamps is approximately 750 hours. Furthermore, this type of lights is more energy consuming than other types, and the majority of the consumed energy is transformed into heat, not light. Higher temperature around the plants may cause the increased invasion of pests and insects, thus these lights are not the best options to use in the indoor gardening.

Fluorescent Grow Lamps

These days fluorescent grow lights (available in various color temperature ranging from 2800°K to 6000°K) are mostly used for starting seedlings and growing green leafy vegetables and herbs. Cool white fluorescent lights are also sometimes used for this purpose. In comparison to the above described lamps, fluorescent ones last much longer (for about 20,000 hours) and emit two times more lumens per watt of the consumed energy. In addition, they are quite cost-effective.

High output fluorescent lamps are even stronger than standard ones: they produce an average 5,000 lumens per 54 watt bulb and can be purchased in warm (3000°K) and cool (6500°K) variants. Their life span is as many as 10,000 hours. Moreover, these lamps are very convenient to use in the indoor gardens with low ceilings due to the fixtures with extremely thin profiles.

Nowadays compact fluorescents (small lamps) are also available for purchase, being the good option to propagate plants and grow larger species. These lights are supplied with the special reflectors to better illuminate the growings. Fluorescents are also produced as cool (6500K) and warm (3000K) lamps with usable life span of almost 10,000 hours. 

Finally, there are also hybrid high output fluorescent/HID lamps featuring cool burning combined with the penetration of high intensity discharge technology. Their advantages include even lighting and wide range of light colors, along with reasonable cost and electricity consumption.

Metal-Halide HID Grow Lamps

The metal-halide HID lamps ensure the growth of the plants almost like under the natural sunlight: their white light ranges from 2700 to 5500 Kelvin with a color rendering index of 65-75. No wonder they are most often used at the places where color rendering is essential: at the supermarkets, manufacturing plants, stadiums, malls, etc. Metal halide lamps, depending on the wattage, may have the usable life span from 10,000 to 20,000 hours. Horticultural metal halide HID lamps feature red light spectrum, which promotes blooming and fruiting.

High-pressure Sodium Lamps

High-pressure sodium lamps have yellow light (2200K) and are characterized with low color rendering index (22). Nonetheless, they are very long-lived: the life span in some cases may be about two years. High-pressure sodium lamps radiate six times more light per watt   of the consumed energy than the incandescent lamps. Their main benefit, however, when used in the horticulture, is the ability to hasten the reproductive stage of the plants growth cycle, improving flowering and fruiting, as well as promoting better and richer yields. This is achieved with the help of the orange/red spectrum of the given bulbs. At the same time, plants grown under these lamps may look unhealthy and pale due to the mentioned color rendering index, which is quite poor. Still, these lights are often used in the greenhouses and indoor gardens (usually as supplemental lights), besides their frequent usage for lighting street and parking lots.

The drawback of these lamps is that they produce much heat, which can cause insects multiplying and diseases development on the plants. To reduce heat production, specifically designed air cooled bulb reflectors/enclosures may be used.

Combination HPS/MH lamps

Another type of grow lamps is combination high pressure sodium (HPS) and metal halide (MH) lamps, where both bulbs types can be enclosed either with two separate ballast assemblies or with a single integrated ballast assembly. Such lights are said to give the perfect spectral mixture of red and blue light along with very good performance.

Switchable, Convertible and Two-way Lamps

A gardener may use either a metal halide lamp or a high pressure sodium bulb with the similar wattage in the same fixture (still, not together) in the convertible, switchable, and two-way lamps. Just insert a metal halide bulb in the fixture when propagating or starting seeds, and then change it with a high pressure sodium bulb during the flowering period of plants growth. Do not forget to place the switch to the necessary setting.

LED Grow Lamps

LED grow lamps belong to the latest developments, which are nowadays successfully integrated into the indoor gardening. They are highly valued by the gardeners for the bright light they radiate, which is in addition of the exact colors necessary for the plants. Moreover, they do not produce much heat and do not need ballasts, consuming at the same time less electricity than some other types of lamps. Finally, they are long-lasting and quite inexpensive.

A LED lamp is made of a number of narrow-spectrum blue LEDs and a much larger number of wide-spectrum red LEDs of specific wavelengths. They say High Power based LED grow lamps may be used for growing various plants indoor. On the other hand, these lights have a big week-point: they consist of the wavelengths perfectly seen by the humans, while plants may need other wavelengths for the ideal growth. Thus, luminous efficiency of LED lamps could have been better to be used for indoor gardening.

Use

Hydroponics, greenhouses, indoor gardening, growing aquatic plants, food production and plants propagation – all of these fields use grow lights. Mostly, it is done on an industrial level, although, non-professional, domestic gardeners are also in a habit of using grow lights.

Increasing light efficiency is often of vital importance for the growers, as the farther the grow light is from the plants, the more of it is lost. Many methods, techniques, and tricks are employed nowadays by the growers to achieve this goal: it is possible to use light reflectors, to whitewash the walls or cover them with reflective materials, to group plants close together, or to move lamps closer to them. For example, incandescent lamps may be placed as close as 24 inches to the plants, while other types of light (those that produce less heat) may be about 4 inches close to the plants.

As for the reflective materials, white and black plastic sheeting is the most common option. The black side is turned towards the walls and the white one faces the plants and works to reflect the light. Using a white paint gardeners choose those with the highest content of titanium dioxide to increase its reflexive abilities. Other types of sheeting include Foylon (foil-laminated fabric), Mylar, or Astrofoil (heat and light reflective sheeting).

Light requirements of plants

It is the real science of adjusting light to the requirements of peculiar plants. Indeed, various herbs need different amount of lighting, and that used in the indoor gardening should mimic that of the natural surrounding. Furthermore, along with the kind of the plant grown one should take into account its growth stage and even size. Thus, having provided optimal light, a gardener may expect the best yields.

Let us say, the richest crops of vegetables is possible to achieve using MH-lamps or fluorescent lamps, which resemble full sunlight. Foliage plants may grow best in the shade, thus, incandescent lamps may be enough for them.

The growers must not forget to allow the plants to “rest” ensuring dark periods (similar to the night in the natural environment). Some plants need many hours of light and short dark periods, while others flourish when both periods are equal.