Grow Lights – An Introduction

While growing up, we all read about photosynthesis and how plants use sunlight, water, and carbon dioxide to make food. Sunlight as we know consists of a number of colors of light together (as seen in a rainbow). It turns out that plants mostly require only two colors, blue and red for their growth.

Fun fact: Plants do not require green light, which is reflected. It’s the reason they appear green.

For the plants to properly grow, they need a certain period of light, known as photoperiod. During the seasonal changes, the length of day and the night(photoperiod) changes, which leads to decreased production. Mimicking the blue and red wavelength present in the sunlight, this problem can be briefly eliminated.

Wavelength between 430 and 460 nm makes up blue light and that between 650 and 700 nm makes up red light visible to the human eye. These are what are also called photosynthetically active radiations (PARs) where the rate of photosynthesis peaks. These wavelengths are provided by the grow lights.

Grow lights consist of electronic lighting systems, which are capable of producing PARs. Grow lights are used, especially indoors and in controlled environment agriculture. These kinds of equipment are used to either supplement or replace the sunlight required by plants. There are different kind of grow lights, mostly categorized into:

  1. Fluorescent Lamps
  2. High-Intensity Discharge Lamps (HID)
  3. Light Emitting Diodes (LEDs)

Fluorescent Lamps

Fluorescent Lamps are what we’ve been used to as CFLs(Compact Fluorescent Lights) and Fluorescent Tubes/Tubelights. These light choices are effective as low-cost solutions, and higher efficiencies. Fluorescent Lamps are more energy-efficient than older incandescent lamps. It means that heat production is lower. Grow lights of this category are often full-spectrum, i.e. the color of lights found in daylight.

As the heat production is low, they can be placed close to the plants for optimization of space. They are also cheap and are cost-effective for the short term and used by beginners.


High-Intensity Discharge Lamps are older technologies but are widely used as grow lights due to the balanced discharge of light spectrum. HIDs are of multiple types, but two of them are used as grow lights. These are Metal Halide(MH) and High-Pressure Sodium (HPS) bulbs.

MH produces a more blue spectrum of lights, along with other spectra of lights including yellow and UV, and lesser red wavelengths. On the other hand, HPS falls more to the side of the red/orange spectrum. UVs in low amounts are also found to induce the production of beneficial chemicals in plants.

The downside is that they’re expensive to set up and produce a lot of heat which can be difficult to manage.

Remember that Blue lights mainly induce vegetative growth in plants while Red lights are responsible to induce flowering and fruiting.

Light Emitting Diodes (LEDs):

LEDs are one of the omnipresent technologies nowadays. Most electrical appliances use these components in different forms. In Controlled Environment Agriculture, LEDs are being widely used. These components are energy-efficient and consistent in terms of light production in nature.

LEDs are cost-efficient in the long run and are up to 75% more efficient than the previous fluorescent lamps. The amount of heat production by LEDs is also negligible. This means that these can be placed closer to the plants than other light sources without damaging the tissues.

These lights are also directional, it means that they throw lights in a specific direction rather than otherwise in previously mentioned lamps. This also reduces the cost of using reflectors to reflect the scattered lights to plants.

In indoor farming, blue and red LEDs are used in different combinations in different stages of plant growth to produce desirable results (known as light recipes). If you stumble upon the picture of LEDs used as grow lights, you might notice that the lights have a purplish hue. This is due to the combination of red and blue lights.

OLEDs: Although OLEDs are expensive at the moment, they’re more efficient than the LEDs and are thinner. OLEDs have rarely been brought into the perspective of agriculture but in the future, this technology might takeover the current industry of LEDs and other grow lights.


All of the above mentioned growing lights have their pros and cons. Fluorescent lamps are the cheapest solutions of all, and for a home grower, that should do it. I’ve come across many people over the internet who are successful home growers and use fluorescents as grow lights. HIDs are more cost-intensive and are HPS are widely used and are found to be beneficial in the flowering stages of plants. LEDs are cost-effective in the long run and can be used in different combinations of LEDs (More blue and less red LEDs for the vegetative stage and vice-versa for the flowering).

LEDs also have high flexibility as the spectrums of light can be fine-tuned according to the need of plants, and as desired. In the case of industrial food production, LEDs seem to be economically viable systems, with a high ratio of return of investment.

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