Ultimate Guide to Buying Grow Lights


Ultimate Guide to Buying Grow Lights

Grow lights come in a variety of sizes and styles, so those just getting started with indoor gardening can quickly find themselves overwhelmed. Choosing the right lights isn’t just a matter of finding a product that fits the grower’s budget. It’s important to take everything from grow light specs to environmental conditions into account. This article will offer an in-depth review of everything novice growers need to know to make an informed decision.

Introduction Part A: Basic Grow Light Comparison

Don’t have tons of time to read up on every factor to consider before buying lights, but want to know what each style has to offer in terms of life span, color temperature, approximate appearance, and general pros and cons? Check out the diagram below to learn the basic differences between the most popular types of grow lights.

Want more in-depth information, including a complete breakdown of each of the points introduced above? You’ll find it in the in-depth chapters following these brief introductions.

Introduction Part B: What (Exactly) Are Grow Lights?

There are three main categories of grow light: High-Intensity Discharge (HID) lights, Compact Fluorescent (CFL) lights, and Light-Emitting Diodes (LEDs). Both Metal Halide (MH) and High-Pressure Sodium (HPS) lights fall under the category of HID grow lights. CFL grow lights include T5, T8, and other models. While there are some noteworthy differences between different lights within these general categories, all products within a general category work in similar ways.

How Do HID Grow Lights Work?

HID grow lights are some of the most powerful lights available to today’s indoor growers. They consist of a glass tube that contains gases, metal salts, and two tungsten electrodes and produce light by passing an electric current between these two electrodes. Here’s a diagram for clarification: 

How Do CFL Grow Lights Work?

CFL grow lights operate on similar principles to HID grow lights, but with a few key differences. Like HID lights, CFLs rely on electrodes to send electricity through inert gases. However, CFL lights produce visible light only after the protons released during this process pass through the bulb’s phosphor coating. Refer to the diagram below for a more visual explanation.

How Do LED Grow Lights Work?

LED lights work a little differently. With LED lights, an electrical current passes through N and P-type alloys separated by a small gap. It is the movement of electrons through this gap that generates light. Here’s a basic diagram for visual thinkers:


Introduction Part C: How Much Do Grow Lights Cost?

We’ll go into budgeting in more depth later, but for now, here’s a basic breakdown of how much different types of grow lights cost:

Keep in mind that growers must consider not just the initial investment required to purchase lights, but also the ongoing costs associated with powering them, replacing bulbs, and compensating for efficiency loss over time.

Introduction Part D: Recommended Grow Lights to Buy

Don’t have time to read through a 7,000-word article, but want to find high-quality lights that will fit your budget? Here are a few options to try:

  • Budget pick: The Sun Blaze T5 by Hawthorne is a fluorescent strip light fixture that makes a good choice for those on a strict budget.
  • Mid-range: The SPYDR 2x by Fluence is a great choice for home and small commercial-scale growers. This LED system was one of the earlier models produced by Fluence and is designed to provide lighting to a 4’x4’ area at just six inches above the canopy, so it’s perfect for grow rooms with minimal space.
  • High-end: The PHYTOMAX-2 by Black Dog LED is one of the most advanced LED grow lights available. It’s expensive, though, so most first-time indoor growers prefer to get their feet wet before jumping in the deep and end buying high-end LED light arrays like the PHYTOMAX-2.
  • Introduction Part D2: Recommended Grow Light Accessories

Some grow light kits come with everything required to set them up straight out of the box, but many require purchasing accessories separately. This can be a blessing in disguise since it gives growers more control over their lighting setups. Here are a few popular accessories to consider:

  • Smart power strips
  • High-quality power cords
  • Premium grow tents
  • Light movers and hangers
  • In-Depth Chapters

Growers who are just looking for some basic, introductory information can follow the links above to find high-quality grow lights that should suit their needs just fine. For those who want to know exactly what they’re getting, the following chapters will offer arguably the most in-depth guide on how to choose grow lights available. Skip around to find relevant information or read through the entire guide to ensure that you buy exactly the right products to meet your unique needs.

1. Distance Between Grow Lights and Plants (Space Available)

One of the most important questions novice growers can ask themselves before choosing lights is how much vertical space they have available to accommodate plants, lighting, and the space required between the two. Room size affects everything from what light intensity growers will need to how high the lights can be positioned off the plants’ canopies. Before discussing things in more depth, let’s look at a helpful graphic that can be used to determine wattage requirements and height requirements in small spaces:


Growers need to know more than just how many watts of power their lights draw to figure out whether they will have enough space to accommodate them, though. Grow light distance charts, also referred to as PAR vs distance charts, will offer growers the information they need to space their fixtures appropriately and determine the right hanging distances, but only once they’ve determined which kinds of lights will be the best fit for their grow rooms. That’s because each type of grow light requires a different spacing between the bulbs and the plants.

Growers who have minimal usable vertical space between the tops of their plants at full height and the light ballasts may be restricted in their buying options if they don’t want to burn their plants. They should seriously consider investing in LEDs or CFLs rather than high-intensity HID lights. Here’s a helpful graphic spaced to scale that offers a good visual explanation of why this would be the case:

Most small-scale growers prefer either CFLs or LEDs thanks to their lower space requirements, but commercial-scale growers may have the space to accommodate medium-watt and high-watt HID systems, which require between one and four feet of space depending on their intensity. This chart offers a good idea of acceptable ranges of distance for HID lights:

Various sources tend to give slightly different advice regarding ideal spacing. When in doubt, follow the recommendations of more experienced indoor growers and, if possible, find experts who specialize in growing the particular crop in question. Bhang has different light and temperature requirements than garden vegetables, for example, so the information available on generalists’ sites may not be accurate.

As a general rule, the stronger a light is, the more room growers will need to leave above their plants’ canopies. That’s why it’s wise to purchase lighting systems that can be moved up and down as plants grow, are harvested, and are replaced by seedlings. Experienced growers use PAR vs distance charts like the example below to determine more precise light spacing.

Some also increase their yields by altering spacing during each phase of plant growth or even use specialized software programs to optimize their grow rooms’ layouts. All that is a little beyond the scope of an article about choosing grow lights, but those who find themselves drawn into the fascinating world of indoor plant cultivation may want to research these subjects further once they’ve gotten the basics down.

2. Heat and Grow Lights

As astute readers may already have guessed, heat output varies substantially between different types of grow lights. That’s why it’s so important to space them appropriately. It’s also why this chapter fully deserves its place near the top of the list of what novice indoor growers should consider before purchasing lights.

Understanding the Basics

Before discussing heat production and different types of grow lights in more depth, it’s worth introducing a few basic concepts. First, all lights produce heat. More accurately, all lights produce infrared (non-visible) radiation, which most people describe in colloquial terms as heat. That’s because the process of converting electricity into light generates three different types of radiation: infrared radiation, visible radiation, and ultra-violet radiation. These three types of radiation, or light, all occupy different areas of the electromagnetic spectrum (see below).

Different types of lights produce these types of electromagnetic radiation in different concentrations. That’s because the efficiency of a particular grow light at converting electrical energy into visible light affects how much infrared radiation it produces. In other words, more efficient lights produce less heat, and less heat is a good thing for growers.

There are two reasons indoor growers are better off buying more efficient lights that produce less heat:

1. High heat can reduce yields and burn plants.

2. High infrared radiation output means the light is producing less visible light, which is what plants need.

How Do Different Grow Lights Compare?

More efficient lights produce less heat. They typically have lower power requirements, as well, but more about that later. For now, here’s what growers need to know about the heat output of each category of lights:

Heat from CFLs

CFLs, including T5 and T8 bulbs, generate more heat than LEDs, but less than HID lights. They have modest power draws and are generally recognized as being relatively efficient.

Heat from HIDs

Both HPS and MH lights generate significant amounts of heat. That means growers will need to place them further from their plants’ canopies and may need to invest in fans and ventilation systems for their grow rooms. Ceramic metal halide (CMH) lights have lower heat outputs, but they’re significantly more expensive.

Heat from LEDs

LED lights are touted for their efficiency and produce only minimal heat. It’s important to note that price points are important with LEDs, though, since heat output typically increases as price decreases. LEDs range substantially in price, but it’s worth investing in high-quality lights.

Quantifying Heat Generation

Heat outputs are measured in British Thermal Units (BTUs). Lighting manufacturers typically include BTU values on their bulbs’ packaging or in their marketing materials, so it’s easy for growers to calculate heat generation for their setups. Just take the BTU value offered by the manufacturer and use a BTU calculator to determine how much the lights will heat the grow room. Keep in mind, however, that BTU calculations offer only general guidelines since factors like insulation, outdoor temperatures, and even ceiling height can all impact heat dispersal in an indoor grow room.

Knowing the exact quantity of heat each type of grow light generates and what kind of effect it will have on grow room temperatures won’t just make it easier to choose a light array. It will also allow growers to determine whether they will need to invest in heat-reducing equipment like fans, ventilation systems, or heat pumps.

3. Know the Key Grow Light Specs: Lumens, Lux, PAR, and Watts

Now that future indoor growers have an idea of how available space and heat generation might impact their purchasing decisions, it’s time to start looking at technical specifications. Light manufacturers use different metrics to measure light intensity and power consumption, the most common of which are lumens, lux, PAR, and watts. We’ll take a look at each of these specs in detail below, but first, a few definitions:

  • Lumens measure the amount of visible light emitted from a single light source.
  • Lux measures how much visible light falls on a surface.
  • PAR coverage refers to the color spectrum of usable light produced by a grow light. There is some debate as to how far this spectrum extends.
  • Watts is the standard unit of power consumption in the International System of Units, with one watt equal to one joule per second.

Now that we’re clear on that, let’s move forward.

So What Are Lumens and Why Are They Important?

As noted above, lumens measure the quantity of light in the visible spectrum emitted from a light source in all directions. When consumers see measures of lumens on grow lights, they can assume that this metric defines the maximum amount of light that their plants could absorb. Without sufficient brightness, measured, to reiterate again, in lumens, plants won’t be able to photosynthesize efficiently and grow.

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