Grow lights are one of the most important elements of an indoor garden. Whether you're a seasoned hydroponic grower or just looking to extend the growing season, buying the right indoor grow light is essential.
In this article, we'll dig into everything you need to know when it comes to choosing and using indoor grow lights.
Last Updated: December 7, 2016
I consider grow lights to be the #1 most important purchase when it comes to an indoor garden. Without them, everything else you need to grow indoors successfully is quite literally worthless.
Most people think that grow lights are only used in very specific situations, but they have a myriad of uses for gardeners of all kinds. Here are a few common ways indoor grow lights are used:
- To grow plants from start to finish in an indoor grow system
- To start seeds in preparation for the spring growing season
- To finish off plants that need a bit more sun than the season is providing
- To successfully propagate and root cuttings
- As a way to extend the daylight hours for plants grown in the sun
- To grow plants harvested at a young age, like baby greens, herbs, and microgreens
Because there are so many different reasons to use grow lights, there are a lot of things to consider when it comes to buying, using, and caring for a light. This article will get into just about everything you need to know when it comes to lights, with links to even more in-depth guides for specific topics.
* Note: This is a very long article. If you're just looking for everything I've ever written on indoor grow lights, click 'Additional Resources' in the quick navigation.
Important Grow Light Concepts
Before we go any further, it's helpful to understand a few basic concepts about lighting in general. By understanding these, you'll be able to see what makes one grow light more suitable for a particular goal than another.
All light — both visible and invisible — falls somewhere on a spectrum. This spectrum is measured in nanometers, which correspond to the wavelength of light. The particular band of the spectrum that we care about as indoor growers is the 400-700 nanometer range, also known as Photosynthetically Active Radiation, or PAR.
As the name suggests, PAR refers to the wavelengths of light that plants can actually use for all of the processes related to photosynthesis. Within this band of light, there are sub-sections that plants use for specific purposes:
- 400-490 nanometers - This "blue" light is used by plants primarily during the vegetative growth phase
- 580-700 nanometers - This "orange-red" light is used by plants during the flowering and fruiting phase
You might be wondering, "What about the gap between 490nm and 580nm? Why don't plants use that range?" Well...have you ever wondered why most plants are green? The choloroplasts in their cells absorb blue and red light, but reflect green light, which just so happens to be the color you see in the 510-570nm range!
See Also: How Does Light Affect Plant Growth?
Now that we know the "type" of light (PAR) that plants need in order to grow, flower, and fruit, we need to look at how "much" of that light we need to use. It doesn't do your plants a lot of good to not be getting enough of the right type of light!
The amount of light is also known as intensity. The intensity of light that is put out by your grow light can vary widely depending on the type of light (covered in-depth below) and the way that you position your light. Proper light positioning is therefore absolutely crucial to a successful indoor grow.
Power refers to how much electricity your grow lights use. It's measured in watts. Different types of grow lights use vastly different amounts of power.
For example, LED lights consume less overall wattage than HID lights. This doesn't mean that LED lights are better, though — there are many more factors to consider.
The footprint of your grow light refers to how much surface area it covers. It's a function of the distance that you place your grow light away from your plants.
The further your grow light is away from your plants, the greater the footprint, but the lower the intensity. The opposite is true if you place it closer to your plants.
Getting the placement of your grow lights correct is a balancing act between the heat output, intensity, and overall footprint of the light. Learning how to place your lights comes with experience.
Learn More: The Inverse Square Law for Light and Hydroponics
Photoperiod refers to how much light you are giving your plants in a 24-hour period. Unlike growing outdoors, you are not limited by the sun, so you can light your plants 24/7 if you wanted to.
Changes in photoperiod are a trigger for some plants. The change signals to the plant that it's time to start fruiting or flowering. If you're growing a plant like this indoors, you'll need to change your photoperiod to trigger the flowering phase of growth.
Types of Grow Lights
Now that we've covered some basic properties of lighting, lets' get into the different types of grow lights on the market.
This is a confusing topic for many growers due to the confusing naming conventions and the sometimes misleading claims of lighting manufacturers.
I hope to shine some light (pun intended) on the different types so you can make an educated decision for your garden.
High-Intensity Discharge (HID)
HID lights are a crowd favorite amongst growers for their impressive light output and relatively low cost
Metal Halide (MH)
Metal halide grow lights are popular during the vegetative phase of a plant's life cycle. This is because they put out more light in the blue range of the spectrum. Plants use far more blue light in their vegetative phase than they do red light.
High Pressure Sodium (HPS)
High pressure sodium grow lights are used throughout a grow, but are especially favored during the flowering or fruiting phase. They put out a lot of red and orange light, which plants use heavily during the final stages of their life.
Ceramic Metal Halide (CMH)
Ceramic metal halide lights are some of the most exciting to come on the market. Although they sound like an offshoot of the classic metal halides, they actually work quite differently.
Growers are flocking to ceramic metal halide lights these days due to their balanced spectral output. They have a great mix of blue, orange, and red light. This makes them an excellent "all around" choice for growers.
Right now, they come in 315w and 630w sizes from a few different reputable manufacturers. The 315w systems typically replace a 400w HPS or MH light, so you're not only saving energy, but also getting a better overall spectral output.
Fluorescent lighting is extremely popular for the beginning stages of a plant's life cycle. Many hobbyist and commercial growers use them for starting seeds, rooting cuttings, and early to mid-stage vegetative growth.
They're extremely efficient from an energy standpoint, don't put out a lot of heat, and come in convenient sizes for indoor growers.
While it's possible to build your own setup with individual CFL bulbs, the standard these days is to use a T5 fluorescent tubes in a variety of sizes. T8 and T12 bulbs also exist, but they're far less efficient and have fallen out of popularity.
When buying T5 lights, you have two decisions to make:
- How many bulbs do you want?
- How long do you want your fixture to be?
The number of tubes in a fixture ranges from 2-16, and the length of fixtures ranges from 2'-4'.
Learn more: T5 Grow Lights Explained and Reviewed
High Intensity Fluorescent (HO / VHO)
There are two more varieties of fluorescent tubes. High output (HO) and very high output (VHO) are the exact same technology, but just put out more light.
Because they are more powerful, they also run hotter, so they must be placed further away from your plant canopy to prevent burning.
Light Emitting Diode (LED)
When LED grow lights first came on the market, they were met with incredible skepticism for two reasons:
- Manufacturers were making incredible claims about their effectiveness and efficiency
- They were a new lighting technology and old-school indoor growers were suspicious
These days, LED lighting is more established and is incredibly popular among some growers. LEDs have a few unique benefits that most other types of lights can't match.
First, they use an incredibly low amount of energy and put out very little heat. This is a big factor for many growers who don't want to spend a lot of ongoing money to light their gardens, and don't have the space to deal with a lot of heat output.
They're also made up of many small diodes, meaning that each diode can be customized to put out a specific wavelength of light.
The most advanced LED lights are custom-built by growers using chip on board (COB) LEDs for maximum light output and customizability.
* COB LED section coming soon.
Plasma grow lights are a newcomer to the lighting industry, boasting incredible claims about their efficiency. In many ways, it feels a lot like when LED lighting first appeared, with manufacturers making outlandish claims to sell units.
There are some unique advantages to plasma grow lights, though. Plasma bulbs last far longer than HID alternatives and put out a more full spectrum of light. They also perform equally when at a lower wattage. In many ways, they're similar to ceramic metal halides.
However, they're also quite a bit more expensive. They're a relatively new technology that hasn't reached the mass market, so prices are still very high.
Learn more: Plasma Grow Lights Explained and Reviewed
Grow Light Cost Calculator
Calculating the cost of running your grow lights is fairly simple:
((Total Wattage x Hours per Day) / 1000) x Cost per Kilowatt Hour x (31 for month, 365 for year)
To make it easier, I've created a simple calculator that automatically calculates the daily, monthly, and yearly costs for your lighting. All you need to do is put in your local cost per kilowatt hour (found on your energy bill) and the number of hours per day you run your lights.
Additional Grow Light Parts
Most (but not all) grow lights need some additional gear to work properly. If you're using HID lights, you need a ballast.
Section on magnetic ballasts is coming soon!
Section on electronic ballasts is coming soon!
Learn more: Digital Ballasts Explained and Reviewed
Reflectors and Hoods
Grow light reflectors and hoods are essential for most types of lighting. As an indoor grower, you want to get as much out of your lights as possible. That means you don't want to waste light output on areas of the garden that you
Maintaining Your Grow Lights
Whatever type of grow light you're using, it's a good idea to follow a few best practices to make sure you're getting the most out of you lights.
These concepts are simple and will allow you to get your money's worth out of your investment in grow lights.
Heat and Cooling
One byproduct of producing light is heat. Different grow lights have different levels of heat output. For instance, LEDs put out very little heat, while a 1000w HPS bulb puts out a lot.
When growing, you must take into consideration how much heat your light puts out and place them far enough away from your plants to avoid burning.
As a general rule, LEDs can be placed the closest to your plants, followed by fluorescents. HID and plasma lighting should be placed the furthest away.
All grow light bulbs degrade over time. Depending on the type, some degrade much quicker than others.
HID Bulb Degradation
HID bulbs degrade over time just like any other bulb, but the reason is different. Every time your turn on your HID lamp, the voltage pulses far above the level it operates at normally.
This pulse damages the bulb every single time you turn it on. After about 6-12 months, the properties of the bulb change enough that the spectral output of the bulb is significantly worse.
T5 Fluorescent Bulb Degradation
Fluorescent lighting degrades much slower than HID lighting. There are a few reasons why this happens, but what you need to know is that they usually only lose about 10% of their lumen output after 20,000 hours.
LED Bulb Degradation
Overall, LED bulbs degrade far slower than other types of bulbs. As a comparison, an incandescent bulb will degrade in 6-9 months the same amount that a LED bulb will in 15-20 years. That is a HUGE difference.
Most manufacturers rate their LED fixtures at 50,000-100,000 hours before bulbs have degraded so much that they need to be replaced.
While true, the temperature that the bulbs operate at is a huge factor in how quickly they degrade. The hotter they run, the quicker they degrade, making the 50,000-100,000 hour numbers drop dramatically.
When to Replace Your Bulbs
No matter how well you take care of your bulbs, you'll need to replace them every now and then.
As a rule of thumb, you should replace your HPS and MH bulbs when they have reached 50% degradation. You can do this with a PAR meter.
For some growers, this is an unnecessarily complicated process. As a general rule, HID bulbs should be replaced every 6-12 months.
Additional Grow Light Articles
- The Best Full Spectrum LED Grow Lights [Updated 2017]
- Metal Halide Grow Lights Explained and Reviewed
- Ceramic Metal Halide Lights: What They Are And How To Use Them
- The Best HPS Bulbs For Your Garden
- How Does Light Affect Plant Growth?
- T5 Grow Lights Guide for 2017
- Plasma Grow Lights Guide for 2017
- Grow Light Reflectors and Hoods 101
- CFL Grow Lights: The Ultimate Guide
- Types of Hydroponic Lighting: What You Need To Know
- Growing Plants with LEDs: An Epic Gardening Guide
- The Ultimate Guide to LED Grow Lights