There are many options for growing plants indoor with artificial lighting. The “best” solution depends on the plants requirements and then the growers concerns. Plants do not use the entire spectrum of light from the sun nor from many of the types of artificial light available. With the dawn of LED lighting, this fact is brought home. Vegetative growth needs more blue light  while flowering requires a spectrum of light with more red/orange. The blue absorption region is 430-450 nm and that of red is 650-670 nm. The grower is normally concerned about two major factors. These are electrical energy consumption and heat. Lets look at the major types of lighting and briefly describe how they stack up to the plant/grower requirements.

Incandescent Lighting

We are all familiar with the normal household light bulb first invented and brought to market by Thomas Edison. So we wont elaborate much on this class of bulb. But it is interesting to compare the different types of lighting to incandescent since it is so familiar to us. Basically this bulb produces light with a filament wire heated to a high temperature by an electric current passing through it, until it glows. The hot filament is protected from burning up via a glass bulb that is evacuated of gasses. This type of lighting is the most inefficient, producing roughly 15 lumens per watt.

Florescent Lighting

A fluorescent tube is a gas-discharge lamp that uses electricity to excite mercury vapor atoms that causes phosphor to glow, producing a somewhat narrow spectrum of visible light. However a fluorescent lamp converts electrical power into useful light much more efficiently than incandescent lamps. The luminous efficacy of a fluorescent light bulb is about (60 lumens per watt) 4 times the efficacy of a incandescent bulb.

High Intensity Discharge Lighting- HID

High Intensity Discharge lamps is a category of lamps containing two very important and popular types of bulbs used in horticulture, Metal Halide (MH) and High Pressure Sodium (HPS). Both are HID’s, a type of electrical gas-discharge lamp which produces light by means of an electric arc between two tungsten electrodes.

Metal Halide Lighting- MH

Developed in the 1960s, Metal Halide Lighting produces light by an electric arc through a gaseous mixture of vaporized mercury and metal halides. Metal-halide lamps have high luminous efficacy of around 75 – 100 lumens per watt compared to incandescence’s 15 and florescence’s 60lu/w. The spectrum of light produced is in the blue range. Vegetative growth requires more blue lighting than other wave lengths.

High Pressure Sodium Lighting- HPS

High Pressure Sodium (HPS) is a HID gas-discharge lamp that uses sodium in an excited state to produce light rather than Metal Halides. High pressure sodium lamps are quite efficient—about 100 lm/W.  The higher powered models of 600 W and above have an efficacy of up to 150 lm/W. Plants in a flowering stage of development require more of a red spectrum, of which the HPS produce more of.

Magnetic Induction Lighting

A Magnetic Induction lamp (also known as Electrode-less Fluorescent Discharge Lamps (EFDL), is a type of fluorescent lamp.  Energy is transmitted into the tube by means of induction. It is induced from the exterior of the tube into the interior without the need of electrodes. There are 2 main types of Induction Lamps, External Inductor and Internal inductor. Both use electromagnets wrapped around a part of the tube (an external inductor lamp), or inserted inside the lamp (an internal inductor lamp). Light is produced by an up-conversion process within the tube where UV light is generated within the lamp by excited mercury atoms The UltraViolet rays are up-converted to PAR light, by a coating of phosphors on the inside wall of the glass tube. By adjusting the type and composition of the phosphors in the coating, PAR wave lengths, used by plant photosynthesis, are produced. The advantages are lower electrical consumption and temperatures when compared to HID lighting. Originally invented and Patented by Nicola Tesla in 1891.  In the beginning, induction tubes were used for indoor and outdoor commercial lighting, as was/is HID, MH and HPS lighting, today. It was then and sometimes now referred to as Plasma Lighting.

Light Emitting Diode Lighting- LED

A light emitting diode (LED) is a light source from a semiconductor, first observed in 1927 and was made into a practical light source by Nick Holonyak in 1962.  All HID lights contain a mixture of gasses within the glass enclosure. The internal temperature and pressure gets quite extreme. LED lights, on the other hand, does not use  gas, operating under extreme pressures and temperatures. In contrast LED lights contain a solid state lighting element, eliminating several risk factors associated with high pressure gases. Led is 70% cooler than HID lighting. This means you can place LED lights in between, on the sides of as well as on top of plants. This places more light where it is needed, as well as reducing the space requirements.

LED Compared To HID Lighting

The HID lights are mostly suboptimal from the perspective of a plant. They only respond positively to specific wavelengths within the color spectrum.

Less than 25% of the power consumed by HID lights is devoted to plant growth. By contrast, 100% of light emitted from the LumiGrow ES is usable by plants.

The Physics Behind LED Lighting

When a LED is turned on, electrons are able to recombine with holes within the device, releasing energy in the form of photons. This effect is called electroluminescence. The color of the light  is determined by the energy band gap of the semiconductor. With a LED system you can produce the color of light needed in the plant growth stage and no more. There for the Watts consumed are in the needed range and no more. This fact makes the LED lighting more efficient than the simple “lumens per Watt” numbers.