Stuppy Greenhouse Blog

Greenhouse Grow Lights

Posted by Phil Bishop on Jun 14, 2017 9:00:00 AM

A grow light is an artificial light source designed to stimulate plant growth by emitting an electromagnetic spectrum appropriate for photosynthesis. Grow lights are used in applications where there is either no naturally occurring light, or where supplemental light is required. For example, in the winter months when the available hours of daylight may be insufficient for the desired plant growth, grow lights are used to extend the amount of time the plants receive light.


Metal Halid (MH)

  • Produce an abundance of light in the blue spectrum
  • This color of light promotes plant growth and is excellent for green leafy growth and keeping plants compact.
  • Best type of light to be used as a primary light source (if no or little natural sunlight is available).
  • The average lifespan is about 10,000 cumulative hours. The bulb will light up beyond this time but due to the gradual decline of light, it is not worth your while to wait for the bulb to finally burn out.
  • If you compare their lumen (brightness) per unit of energy consumed, metal halides produce up to 125 lumens per watt compared to 39 lumens per watt with standard fluorescent lights and 18 lumens per watt for standard incandescent bulbs.

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High Pressure Sodium (HPS)

  • Emit an orange-red glow
  • Triggers hormones in plants to increase flowering/budding in plants
  • They are the best grow lights available for secondary or supplemental lighting (used in conjunction with natural sunlight). This is ideal for greenhouse growing applications.
  • Their average lifespan is twice that of metal halides (but after 18,000 hours of use, they will start to draw more electricity than their rated watts while gradually producing less light)
  • HPS bulbs are very efficient. They produce up to 140 lumens per watt.
  • Their disadvantage is they are deficient in the blue spectrum. Most plants will grow up thin and lanky.

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Light Emitting Diode (LED’s)

  • Can be designed to emit red, blue, white, green and UV light. Very customizable.
  • Have the option to be dimmable.
  • Very efficient.
  • Higher upfront costs but this is slowly coming down as production costs of the lights also comes down.

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Fluorescent Grow Lights

  • 75 to 90 lumens per watt making these lights energy efficient and extremely effective especially when used in numbers.
  • Fluorescent grow lights also have better color rendering properties (more of the light emitted is used by the plant) and produce much less heat than incandescent and HID grow lights.
  • This allows them to be placed closer to plants (within a few inches) greatly decreasing lumen loss from the bulb to the plant. It is recommended that these lights be placed no more than a couple feet from the plants for best results. 2700k to 3000k bulbs provide higher output in the red spectrum which promotes flowering. 5000k to 6500k bulbs are full spectrum with much of the light in the blue spectrum which promote overall green plant growth.

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Incandescent Grow Lights

  • These lights are the most inexpensive to purchase but are also the most inefficient and a poor source of light for plants.
  • At best they can provide supplemental light to individual house plants.
  • Incandescent lights have a low lumen output per watt compared to HID and fluorescent grow lights. New smaller CFL grow lights, 40 watt, produce as much light as a 150 watt incandescent bulb, and more of the light is used by the plant. This type of bulb will pay for itself in energy savings the first 60 days of use.


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Topics: greenhouse equipment

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