The Importance of Light Spectrum in Grow Lights: Incandescent, Fluorescent and HID

Posted on 23rd April 2011 in Gardening, Uncategorized

Growing your own plants indoors gives you many advantages. It allows you to grow plants regardless of the season which assures you fresh vegetables and herbs year-round. Also, it’s a great way to give your plants a head start during frost and relocating them when it’s most convenient.

When choosing your lighting setup, an important factor you must consider is the light spectrum you are providing your plants with. There are different types of bulbs available, and this article will provide some insight on the light spectrum you need, and what you can expect from them.

When plants are outdoors they receive all the benefits from direct sunlight. The daylight they get changes over time allowing your plants to absorb what they need from the different spectra and do their photosynthetic process. For example, during spring when plants are vegetating, the natural daylight color temperature is around 6000K and it appears blue for the most part. When plants bloom in summer daylight appears in a red-orange fashion.

The bottom line is that your plant will require different spectra, meaning the color of the light, for every stage it goes through. This is very important because when growing indoors your goal is to mimic the conditions as if your plant was outdoors as close as possible. Also, every plant will have different requirements, some will need more time of light or darkness, and intensity of brightness (this is measured in Lumens per watt).


Incandescent lighting is hardly appropriate by itself to provide an environment in which your plant will thrive. It is the most inexpensive option, but because they will put out a red-yellow color, and their color temperature is very low (around 2700 K) they will not provide the kind of light your plant will grow from. They’re life-span is about 750 hours and they’re less energy efficient than any of the other options available.


Fluorescent grow lights are available in color temperature ranging from 2700 K to 7800 K, which covers your plants needs along every stage of its growth. They are mainly used to grow seedlings to get a head start on spring plantings. They produce twice as many lumens per watt as incandescents and they last between 10 and 20 thousand hours. You have a choice between High Output and Compact. The former is most commonly used and the latter is for propagation more than for giving direct light to the plants.


High Intensity Discharge grow lights produce the most brightness of all options, and they are the ideal choice for optimum results. There are two types within this category: Metal Halide and High Pressure Sodium lights. The first one produces light in the blue spectrum, while the latter does it for in the red-orange.

There are products that combine the two, but they are more expensive, have a shorter life-span and they have smaller bulbs which compromises the distance covered by the light.

In order for your plants to use most of the light provided, and avoid waste, you will want to provide the correct temperature and brightness level according to the type of plant you have and the stage of growth where it is at. At the time being, HID or Fluorescent will give you good results. LED grow lights are the latest trend, but because they’re a fairly new technology there isn’t much instruction on how to use them properly.

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