Here's the deal:
If you're reading this article, you've probably heard of grow lights.
But you may still have questions...
Which grow lights are best?
How do you use grow lights?
How far should grow lights be from plants?
We will answer all those questions.
But before going any further...
Let's quickly define what a grow light is.
According to wikipedia, a grow light is:
"generally an electric light, designed to stimulate plant growth by emitting an electromagnetic spectrum appropriate for photosynthesis"
But you are still likely wondering:
In this article we will be covering a basic overview of different grow light types.
For a more detailed rundown, look at these links:
1. Lighting Indoor Houseplants: University of Missouri Division of Plant Sciences
2. Growing Herbs Indoors with Growlights: Penn State University Extension
3. Indoor Lighting For Plants: University of Vermont
Now for a more general run down, keep reading:
Before we go any further, you need to know that one of the key factors to your success in indoor urban farming project is your lighting.
You're almost certainly going to need some type of grow light.
Grow lights DO actually work.
In fact, grow lights completely solve one of two huge obstacles for growing indoors...
They will either:
1) supplement sunlight
Grow lights don't always have to mimic sunlight exactly.
in some cases:
2) completely replace direct sunlight.
In some applications, grow lights are designed to optimize growth and improve over sunlight by providing certain spectra during the growing process.
(see diagram below)
Grow lights can be used to effectively grow produce in urban settings indoors with little or no sunlight. Source: Growsomething Green
Grow lights come in a couple different varieties, and they can replace sunlight, supplement sunlight, or even optimize over sunlight (above)
A basic explanation of how photosynthesis works Source
Plant's grow via the process of photosynthesis, which requires light. But not just any light...
Light absorption in plants occurs due to a compound found in all plants: chlorophyll, specifically chlorophyll-a and chlorophyll-b, which absorb the red and blue light spectra.
Why don't plants absorb all light?
The first plants ever grew in the ocean millions of years ago, and red blue light penetrates underwater effectively.
Plants can grow underwater because of the specific light spectra they absorb. Source
How is this related to urban farming?
If a plant is receiving proper light from the red and blue light spectra, it will grow, just like with sunlight.
The following lighting styles we will discuss in detail may not seem as powerful as sunlight or may not "look" like sunlight, but because they provide the necessary spectra, they get the job done.
There is more than one type of indoor grow light, and some may be better or worse for your specific needs.
To find out what is best for your application, let's get into the details.
In the rest of this article you will learn:
- the 3 fundamental types of grow lights used for indoor urban farming
- which types are better for urban grower beginners
- specific details, pros, and cons of each type of light style, plus any other interesting tidbits you may find useful
The three main categories of grow lights are
1) Fluorescent lights
2) high-pressure sodium (HPS) sometimes referred to as HID (High intensity discharge)
3) light emitting diodes (LED)
Incandescent lights (common light bulbs) can also be used.
We will discuss why incandescent light for urban farming will never be the best idea at the end of this post, but first...
Yes. Fluorescent lights will commonly be used for growing vegetables and herbs indoors. There are two main types of fluorescent bulbs: Fluorescent tubes and Compact Fluorescent Lights (CFL's). More details below:
Fluorescent tubes come in a variety of intensities, more efficient and longer lasting than incandescent bulbs but not as intense as HPS lighting (discussed later).
Another advantage of fluorescent tubes?
They are relatively thin and can fit well into small spaces.
One downside of this type of fluorescent light is that they will usually require a ballast to regulate current and the tubes will require a stand instead of a conventional socket (all in one systems including stands and ballasts can be purchased but will usually be more expensive).
Diagram: How a ballast regulates tube current in fluorescent grow lights
Compact Fluorescent Lights are overtaking use of traditional incandescent bulbs for all lighting use cases (not just for urban farming).
This change is mainly due to the superior efficiency of CFL over incandescent and advances in technology for mass producing CFL's over the past several decades.
(CFL technology is over 100 years old but at first was too expensive to produce at scale).
Details to know about CFLs:
- emit large amounts of light in blue and red spectra in most models
- use 20% - 30% of the energy of traditional incandescent
- 8x -16x lifespan of incandescent
- energy efficiency rating of 7-15%
- available at major hardware stores, cheapest light investment of all 3 major types
CFL's have light peaks in the blue (425-450 nm) and red (600-700 nm) spectra (above) Source
As a basic rule, the closer the bulb is to the plant, the more efficiently you will be using your light. For urban farmers who are growing for a profit, more efficiency = more margin.
How does CFL help urban farmers who sell their crops?
The key advantage with CFL is that they don't emit much heat onto the plants. This means that you can keep the lights closer to the plants without causing too much heat, resulting in high lighting efficiency.
One additional advantage of CFL is that it will be more convenient and cheaper to implement than some tube style fluorescent, fitting into conventional power outlets without any modification required.
For these reasons, if you are just starting out, an extremely easy first step is to just buy a CFL bulb and see what happens on a small scale, especially with vegetables or herbs that have less light requirements, like dill.
Growing roses indoors with high pressure sodium (HPS) lighting. Source
Background: High pressure sodium lights (HPS) are a category of lights growing in popularity and overtaking fluorescent use, especially by more experienced and commercial growers.
Origin: The technology originated nearly 75 years ago
Tips and details for HPS:
- there are, in fact, LPS lights (low pressure sodium) on the market, but they are not great options for growing indoors (mainly due to improper yellow spectra that they emit)
- HPS will generally require a greater distance from plants. This is because they generate considerable amounts of heat and are more powerful bulbs.
- HPS will almost always require significant investment to set up, the system needed to manage heat and ventilation requires extra complications in the HPS set up process.
Suggestion: We would not suggest HPS lighting for beginners. With high set up costs and more complications than other options, the upside of this higher power lighting is not likely to be worth it for you.
LED's for indoor urban farming...
Origin: The first LED's were developed in the early 1900's, however categories of red and blue spectra emitting LEDs suitable for urban farming and gardening indoors were not widely in use prior to the 2000s.
Details to know for LED indoor urban growing:
- LED's are by far the most efficient of all three major types: they regularly have light efficiency above 20% (CFL's are usually about 1/2 as efficient). Recent LED models have had over 60% light efficiency.
- light is much more focused. the result is that LED lights can be placed farther from plants and light doesn't quickly loose focus with distance
- zero or near-zero heat production by LED lights
- specific wavelengths can be targeted within color spectra, resulting in customized "plant therapy" lighting that can even improve lighting over sunlight.
- Protection often necessary for eyes when urban growing. Light can be harmful to human eyes
- Prices can be much higher than CFL
- Efficiency can sometimes best be captured at scale only. To elaborate, red-blue LED bulbs found in large retail stores will a) likely not be the optimum power amount for growing (too low) and b) will not be provided at a scale to allow energy savings to make economic sense
- For urban farming for profit, be sure to purchase a larger LED system online, you will realize ROI on the system much more quickly.
The benefits of LED lights over HPS lights Source
Incandescent bulbs are better than no light at all, but they have multiple issues:
1) extremely inefficient from a cost perspective
2) do not produce the correct wavelengths of light needed for plant growth (see image below)
Incandescent bulbs are not ideal for plant photosynthesis (400-700 nm range) source
When you are deciding which grow lights to purchase, here are some basic guidelines to follow:
1. Wavelength: Focus on the wavelength emitted by the lights you are purchasing, remember the ranges for red (600-700 nm / 3000 K ) and blue (425-450 nm / 9000 K)
translating wavelength in nm to color temperature in Kelvins source
2. higher watt bulbs leading to more light intensity, higher wattage bulbs will require more energy to operate
3. Pick between energy efficiency and cost efficiency: LED lighting may be more efficient than CFL, but CFL can be set up fairly easily and at a low upfront cost out of pocket for urban farming beginners.
- Lumens measure human visible light and therefore will not be great indicator of light for plant growth
- Again, try to avoid high pressure sodium lights if this is your first project
Our Pick: CFL (Fluorescent lighting)
- Availability: Wide variety of CFL options with effective wavelengths will be available at a hardware store near you.
- no need to order online where product quality can be hard to gauge or find vendors carrying special types of lights that may not have stores near you
- Fixture Size: fixtures for holding lights will be smaller and therefore easier to work with. For example, many LED lights will have large fixtures that are either all on or all off. With CFL, you will usually have the capability to turn on only part of the light set if necessary and conserve power.
- Able to use at all stages of plant development: CFL's will usually be suitable for developing seedlings before transplant. More high powered systems will be too powerful for seedlings.
- Less Heat: you can add onto your original system without hurting your plants, CFL has such low heat creation that adding more bulbs to your system will not lead to overheating.
- there are 3 types of grow lights you should know about: fluorescent lights (CFL), high-pressure sodium lights (HPS), and light-emitting diodes (LED)
- while LEDs are the most efficient grow lights, they are less readily available and have a higher upfront cost than CFL
- CFLs have a low upfront cost and are widely available at most retail stores selling light fixtures, but they are less efficient than LED
- High pressure sodium lights require upfront investment and may be difficult to manage for beginners because of the set up process and veniliation and heating issues that HPS presents
- incandescent bulbs (traditional bulbs are also usable in a pinch but in most cases you won't see great and repeatable results
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