The Grow Lights Effect on Plants

Taking notes of plants 2 - The Grow Lights Effect on Plants

There are many grow lights on the market, but how do they work? Here’s a primer on the effects of high-intensity discharge (HID), LED, and metal halide lighting. Let’s examine some of their benefits and drawbacks. For the most part, these lights produce similar results, though the color of each can vary. High-intensity discharge is the most widely used, followed by Metal halide and high-pressure sodium.

High-intensity Discharge

High-intensity discharge is the latest technology used to light indoor gardens. It produces less heat and consumes less electricity than standard grows lights. These lights are especially effective for indoor growers who want to reduce the heat produced by their lights. Despite the advantages of LEDs over high-intensity discharge, there is a hidden cost to consider when choosing the right to grow light. Many growers are switching over to LEDs in their indoor gardening projects.

The main difference between LEDs and HIDs lies in the light spectrum. Metal halide lights produce a blueish spectrum while Ceramic Metal Halide lights produce a cooler white light. Metal halide lights are generally the best choice for vegetative plants, though high-pressure sodium lights are acceptable for blooming plants. The first light-emitting diode (LED) was invented more than a century ago by Henry Josef Round. While the color of this light was not actually purple, the effect made it appear to be so. It has been nicknamed “blurple” by some, but this has now become a derogatory term.

Metal Halide

There are a few things to consider when choosing the best type of grow light for your crops. The first consideration is the area you will be the lighting. The size of the bulb will determine the area you will cover. A table will show you the maximum area each wattage covers and how far away your plants should be from the light source. Additionally, you should consider the reflector or ballast you will use for your lights. Using a standard light socket will not work with metal halide bulbs.

Plants react differently to light depending on the season. The blue spectrum is associated with spring and promotes vegetative growth. The red spectrum promotes flowering and the reproduction process. Plants adapted to the red spectrum will lose color and stretch during flowering. This effect is most noticeable in flowering plants. Then again, blue metal halide bulbs produce light that is closest to that of sunlight. This results in a more uniform color and size in flowering plants.

High-pressure Sodium

Plants on a table 1 - The Grow Lights Effect on Plants

While many plants prefer the blue light provided by metal halide, high-pressure sodium bulbs provide a wider spectrum that can mimic red sunlight. These high-pressure lights mimic a spectrum that consists of red, yellow, and green. Their spectrum can mimic either morning or evening sunlight. The following are some benefits of these grow lights. High-pressure sodium growth lights can be used during early or late vegetative growth stages, as well as during the fruiting phase.

The effect of LEDs on the growth of crops is comparable to that of high-pressure sodium grow lights. LEDs emit light when particles carrying current combine with an electrolyte. LEDs also use less electricity than HPS lights. However, they do not produce the full spectrum of light that HPS lights provide. Full-spectrum LED grow lighting has the potential to match the performance of traditional light sources. But the question remains: Which type of grow light is right for your plants?


When using Indoor Grow lights, you should know about the spectral output of LED grow lights. The wavelength of light a plant responds to improves its growth, quality, and productivity. Generally, blue light stimulates chlorophyll production, while red light promotes growth and flowering. Red light is also beneficial for growing long-day plants under short-day conditions. However, not all plants respond to the same wavelengths.

When using high-power LED grow lights, it’s important to choose the right one for your needs. Plants need illumination for about 12 to 16 hours a day. They require some dark time to enlarge and grow. If you use a low-wattage grow light, you may be burning the plants instead of growing them. For this reason, you should match the wattage of the LED grow lights to the surface area of your plants.

Lighting intensity has a direct impact on plant cell proliferation and organ differentiation. LED grow lights affect all stages of plant growth differently. Seedlings don’t need a high light intensity to start but need the right amount for proper development. With each successive stage of growth, light intensity increases. As a result, LED grow lights play a crucial role in flowering and fruit sets. Hence, a balance must be struck between providing the necessary amount of light while avoiding over-illuminating the plants.


The Grow lights effect in plants depends on three factors: the quality of light, the intensity of illumination, and the duration of illumination. In general, they should be placed about 12 inches (30 cm) away from the plants. The lower-wattage LEDs should be placed about 12 inches from the plants, while the higher-wattage LEDs should be positioned at least 36 inches (91 cm) away from the plants. Growing plants under these lights should be done in indirect sunlight, as the light from direct sunlight is reflected by the leaves and stems.

The intensity of the light also affects organ differentiation and cell proliferation. Different levels of light intensity are required for different growth stages of plants. However, preliminary plants do not require high intensity and can only benefit from a moderate amount of light. As they grow, the light intensity increases accordingly. For example, higher intensity is needed to produce a robust seedling. Similarly, the LED grow lights affect the rate of flowering and fruit set and ultimately the productivity of the plant.


While fluorescent grow lights provide high light output, they also produce less heat. Both types produce light intensity and duration that are usually measured in foot candles. Intensity refers to the length of time a light source sheds radiation. During the day, the sun sheds about ten million-foot candles of light. A fluorescent grows light emits about nine-foot candles of light per hour, while an incandescent bulb provides about seven-foot candles per hour.

For seedlings, a full-spectrum, high-output T5 light is ideal, as it drives growth from the seedling stage until it is ready to be transplanted. However, some people are opting to replace their fluorescent grow light fixtures with LED bulbs, and some farmers have reported good results using T5s in their crops. Fluorescent grow lights also contain mercury, a highly toxic heavy metal. Once they break, the mercury vapor escapes and pollutes the environment.

Spectrum of Light

This study has demonstrated the spectrum of light effect on plants and how it affects their growth. The plant’s light response is governed by three variables: absorptance, reflectance, and transmittance. For lettuce, absorptance was highest in the 400-500 nm region. This value decreased after reaching 551 nm and increased as wavelengths increased. The absorptance decreased steadily after reaching 5% at 666 nm.

The green spectrum is governed by chlorophyll, a chemical that does not absorb green light as readily as other wavelengths. The result is that plants appear green because their leaves reflect between ten and fifty percent of green waveband photons. In fact, these leaves absorb almost 90 percent of green light, while transmitting only 1% of red and blue light. This color spectrum plays a crucial role in photosynthesis, and further study may provide clues as to how best to deploy it across a variety of crops.

In addition to providing energy for photosynthesis, light also functions as a source of information. Various spectra of light give plants information about their surroundings and how to survive, reproduce, and grow. Generally, developmental response in plants is triggered by the light spectrum from 300 to 800 nm. Both UV and infrared light are known to play a role in plant morphogenesis. Various species have different types of photoreceptors that respond to certain wavelengths of light.


How much electricity will you need for your grow lights depends on the kind of lighting you choose and how long you need them on. Most plants require a full 12-hour day of light to grow well, but some will tolerate long periods of light, but this comes with a price tag and only a marginal benefit. In most cases, 12 hours a day will do the trick. Electricity costs are measured in kWh or kilowatt-hours.

The cost of runtime for grow lights can be high, but if you have an energy-efficient lamp, it will be worth it. Unlike traditional lamps, grow lights can be adjusted to provide a particular spectrum. Moreover, many come with added functions, such as anti-leakage and waterproofing. You should also consider the material from which the grow light is made, as that will determine its price. To save on electricity costs, try to purchase a grow light made of a low-wattage metal.


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