How to Choose the Right Grow Light for Hydroponic Gardening

If you are aiming to grow high value crops through indoor or outdoor gardening, an important element to be focused is the ‘Light’ and choosing the Right Grow Light! The two different types of grow lights that are used viz. Metal Halides (MH) and High Pressure Sodium (HPS) lights. Both are High-Intensity Discharge lamps, capable of producing light within the visible range of spectrum through an electric arc between the electrodes placed inside the arc tube. Let’s go through these two variants of grow lights in detail:

Metal Halides (MH) Grow Lights

MH grow lights are used for indoor growing applications, in short, for growing plants indoors because of the wide spectrum. It is comparable to mercury vapor lamps, but hold added metal halide compound in the quartz arc tube, which improves efficiency and color rendition of light. An MH light contains a mixture of mercury, argon, xenon and different kinds of metal halides compounds, namely bromine and iodine inside the compact arc tube made from fused quartz or ceramic.

The mechanism behind generation of light is – on application of voltage, the gases get ionized which further aids the arc to strike across the electrodes. This results in generation of heat and subsequently mercury and metal halides vaporize to produce the light within its respective spectrum. MH lights have high luminous efficiency of around 75-100 lumens per watt and produces intense white light.

The unique characteristics of Metal Halide lights are:

  • Long shelf Life: An average life of 15000-20000 + hours
  • Superior Light Quality: Output is closer to natural sunlight
  • Designable color: Designed to produce almost any color temperature preferred from 2,700K to 20,000K. Special colors including blue, green, aqua and pink can also be produced.
  • Exceptional color rendering: 65-90 color rendering index
  • Compact size: Generates light from compact light source
  • Flexibility: Unaffected by ambient temperature, extensive wattage options
  • High Efficiency: Generates 65-115 lumen per watt, higher than incandescent, fluorescent or mercury vapor lamp
  • Positive environmental Impact: Less pollution due to lower electrical power generating requirement.

The light generated by Metal Halides falls under the blue range of the electromagnetic spectrum which is needed by baby plants in their vegetative state. The blue spectrum of light is best suited for plants during early stages of development and also for promoting compact growth and strong root system. The color–rendering index of such lamps is within the range of zero to 100; wherein a rating of 80 to 100 is indicative of good quality white light.

High Pressure Sodium (HPS) Grow Lights

High pressure Sodium lights (HPS), work under a common phenomenon of excitation of metal which in turn releases energy in terms of photons or visible light. As the name suggests, HPS based light source consists of an alloy of metallic sodium along with mercury (amalgam); which is packed inside an arc tube. Aluminum oxide is used in assembly of this arc tube and the amalgam is crammed under high pressure. A specific amount of sodium gas reacts with electricity, subsequently charging the atoms. These charged atoms then lose their energy in the form of light waves and the wavelength of this light waves mimic natural sunlight best suited for optimum growth of plants.

Greenhouse growers around the world use HPS grow lights to improve bud set, increase growth and create artificial growing environment to guarantee production out of season. HPS lights work in conjunction with metal halides, especially mercury and produce light usually ranging from dark pink to intense pinkish orange of the electromagnetic spectrum. The color varies with the intensity of heat absorbed by sodium. Another characteristic feature of HPS light is its potential to generate bluish white light instantly when mercury achieves high pressure arc discharge just before sodium gets warmed. Though the atomic emission lines are of both mercury and sodium, the characteristic color is dominated by sodium D-line emission. Such a broad spectrum of light provides energy needed by plants for carrying out various physiological processes like synthesis of chlorophyll, photosynthesis, flower production, fruiting, and ripening.

Pros of using HPS grow lights:

  • Although relatively expensive than fluorescent lights, they are much more energy efficient than fluorescent lights. They can be adjusted for lower light uses and their efficiency can be improved by attaching a timer into the ballast.
  • They are durable, long lasting and easily portable. The bulbs weighs less and the fixtures attached can also be removed, replaced and modified with an ease. All these attributes further lower the maintenance costs.
  • HPS lights are highly conducive for plants grown inside greenhouses. They are used as supplements for natural sunlight as the spectrum of light emitted by them aids in budding, flowering and fruiting, of plants.

Here is the summary on what we have covered about Metal Halide and High Pressure Sodium Grow Lights:

HPS is superior to MH in terms of efficiency, longevity and quality. However, to get the best results, install conversion bulbs, i.e. use MH during vegetative phase and then switch to HPS during flowering. Hope you got the right way to choose the right grow light for hydroponic gardening.

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