If you are reading this there is a good chance you’re considering growing indoors, which means you’ll need to buy a grow light. The problem with starting fresh is that there is so much information online, it is hard to know what is accurate and what is not, and you might come away with more questions than answers about lighting.
You might have heard about PAR maps, PPFD, spectrum, and efficacy, but what do those mean and how do you use those terms (and more) to guide you toward finding the perfect light for you?
We put together this article to help guide you through understanding what a “grow light” is and how to choose the right one for your needs.
What is a Grow Light?
A simple question without a simple answer: what is a grow light? A grow light is any type of artificial lighting that uses an electrical current to produce light in the visible spectrum, which plants use to go through the process of photosynthesis.
We use grow lights by hanging them above a plant so that light shines down upon the plant(s) evenly, allowing the plant to absorb as much light as it can without getting burned.
A good grow light will imitate the most useful parts of sunlight – the “useful” part of sunlight for a plant coincides with the visible spectrum – all the colors from violet to red and including a few fringe colors that our eyes cannot see like ultraviolet and infrared light.
For the purposes of growing indoors, there are three primary types of lights, some require extra equipment to operate while others come complete and can be plugged directly into your wall outlet.
These three types of lights are:
- High-Intensity Discharge (HID), including Metal Halide (MH), Ceramic Metal Halide (CMH), and High-Pressure Sodium (HPS)
- Light Emitting Diodes (LEDs)
- T5 Fluorescent
In the next section, we will use terms like “temperature” measured in Kelvin (K), “light wavelength” measured as nanometers (nm), and “peaks” in wavelengths. We discuss exactly what those terms mean in the “How Does a Grow Light Work” section.
How Does a Grow Light Work
A grow light works by emitting energy in the form of light but in creating light, bulbs will also emit heat as a byproduct of the process. This heat can be a positive byproduct if you are growing plants in a cold climate or plants that prefer higher temperatures, or it can be a negative byproduct if you live in a warm climate, have trouble controlling humidity, or want a lower temperature range.
A grow light pulls electricity from your electrical socket and likely uses a ballast to convert the 120V electrical current into a wattage that is usable by the bulb. The grow light’s efficiency at converting your home’s electricity to the light put out by the bulb without losing some of that electricity in the process is called its efficacy: the less energy lost in the form of heat and by powering the conversion.
If you want to understand the relationship between your electrical outlet and the energy put out by your light better, you’ll need to understand the relationship between voltage and wattage, which can be found here.
Plants mainly utilize light that is within the visible spectrum or just outside of it. Therefore, grow lights aim to produce the exact coloration that plants desire – this allows for the most efficient use of electricity while having the best results.
We measure color wavelength in two ways: nanometers (nm) and Kelvin (K). Nanometers refer to the actual wavelength of the light, measured from peak to trough, while Kelvin refers to the “temperature” of the light.
Via Wikipedia
Via Wikipedia
For more about how light coloration and temperature affect plant growth, read our next section, “What Color of Lights Do Plants Grow Best In.”
Now, something important to remember when we are talking about light is that light is subject to the laws of physics and all the strange, quirky reality that comes with it like the fact that light is both a wave and a particle simultaneously! Light arrives as a “photon,” which is essentially the carrier of the electromagnetic force, and is the quantum form of all electromagnetic radiation, whether that be from the Sun or your growing light.
When light is delivered (falls or pours) to a surface, it arrives as a photon or a packet of electromagnetic radiation, and we can measure this arrival to help us see how effective our grow lights are at covering a surface!
We measure the number of photons that arrive in a given area through a term called the Photosynthetic Photon Flux Density (PPFD for short), which is then mapped onto what we call a Photosynthetic Active Radiation (PAR) map. Big terms, but both of these are quite important for growers! Let’s take a look at why that is.
PPFD measures the number of photons that arrive in an area over a given amount of time. PPFD is measured in micromoles per square meter per second (µmol/m2/S). Usually, the higher the number the better.
A PAR map shows a comparison of PPFD spread across an area. One of these maps should be included with every grow light and they will look like the one below.
This PAR map is from the VIVOSUN VS4000. It says that the VS4000 was hung 12 inches above the floor and covered a 5×5-foot space. In the center of this map, we can see the PPFD is very high, while near the edges the PPFD is much lower, which is to be expected as the light coverage is weaker. An analogous example would be shining a flashlight in the dark and noticing that the light looks weaker around the edges of the coverage.
What Color of Light Do Plants Grow Best In
Now we have covered light “intensity” and “coverage” with a PAR map and PPFD, let’s consider how light coloration factors into growing a plant.
Plants go through four main stages of growth: germination, when the seed sprouts its taproot and first shoot; seedling, before the seed grows its first set of true leaves; vegetative growth, when the plant has its first set of true leaves until it matures to be ready to flower and reproduce; and flowering, when the plant produces flowers for reproduction and is mature enough to spread its fertilized seeds.
Through each stage of growth, a plant will utilize a specific coloration to produce the amino acids that it requires to build the structures of that stage. The germination stage does not require specific light so we will omit it here. Let’s look at the details.
| Stage of Growth | Color Preference (higher -> lower) | How the light is utilized (sources: 1, 2) |
| Seedling | Blue, blue-green | Blue: The opening and closing of stomata; helps develop thicker, robust foliage; stimulates amino acid production for structural compounds (1) |
| Vegetative | Blue-green, red, ultraviolet | Blue: The opening and closing of stomata; helps develop thicker, robust foliage; stimulates amino acid production for structural compounds (1); Red: promoting elongation and growth, mediating flowering (2) |
| Flowering | Red, blue-green, infrared, ultraviolet | Red: promoting elongation and growth, mediating flowering (2)
Blue: The opening and closing of stomata; helps develop thicker, robust foliage; reduces stretching (1) |
Yet, when growing a plant, there can be such a thing as too much light, both in terms of intensity (see “how high should I hang my lights” for further information) and in terms of coloration.
Too much blue light and not enough red light: this is hard to do, but if your plants receive too much blue light and not enough red light they will likely grow smaller, develop brown leaves, and will die.
Too much red light and not enough blue light: your plant will start to “stretch” by developing elongated stems and branches.
Types of Grow Lights
These three types of grow lights have a lot of variation of styles within their respective categories, whether that be wattage (which corresponds to size – higher wattage requires a larger light), layout or style, or required accessories like fixtures and reflectors.
High-Intensity Discharge (HID) Lighting
HID lighting has been a very popular choice for growers for decades because of its cheap components, reliable results, and industry standardization through over a century of technological development. HID bulbs operate by passing an electrical current through a pressurized tube filled with a type of chemical that, when heated, emits light. Different chemicals produce different colors. Plants prefer specific colors at specific periods of growth, so different light bulbs can be used to match these preferences.
High-Pressure Sodium (HPS)
HPS bulbs have dominated the HID industry for decades and are still one of the most popular lighting options on the market. This isn’t surprising: HPS consistently demonstrates that it grows some great plants that provide huge yields.
HPS bulbs create light by passing an electrical current through pressurized sodium gas, which emits a warm orange-red light. Because of this, HPS bulbs are excellent for flowering plants, but they also excel at growing during the vegetative stage.
HPS bulbs require that you use a reflector and a ballast, which adds an additional cost but does indeed help with directing light.
Metal Halide (MH)
Metal halide lamps are an old technology going back to the beginning of light bulbs. Metal halide bulbs use another noble gas that, when heated, emits a white-colored light that mimics the temperature of light during early spring, so these lights are great for early life growth to vegetative growth.
These bulbs also require a ballast and a reflector to operate and usually do not do very well during the flowering stage of growth because they do not provide enough red light for flowers and buds to develop properly so they have fallen out of favor with many growers.
Ceramic Metal Halide (CMH)
CMH bulbs are a relatively newer technology for HID systems. They are an improvement on MH technology and produce a wider spectrum of light by using a more refined mixture of noble gasses and a ceramic plate where the electromagnetic process takes place.
CMH bulbs are a major improvement in the industry and have shown great results, yet there is some hesitancy to adopt the new technology because LED lighting emerged and gained all the attention. That said, CMH bulbs are relatively inefficient because they emit a lot of heat and require a ballast and reflector to operate.
| HID Type | Temperature (Kelvin) and coloration | Matches with (growth period)… |
| High-Pressure Sodium (HPS) | 2700K; emphasis on yellow, orange, and red (580-630nm) with an additional peak at far-red and infrared (820nm) color | Predominantly flowering, but also vegetative |
| Metal Halide (MH) | 4200K; emphasis on blue (365-435nm) and green/yellow (540-580nm) color | Predominantly seedling and vegetative |
| Ceramic Metal Halide (CMH) | 3100K; emphasis on green/yellow (565-590nm) and red (590-625nm) color | All stages of growth |
| HID Type | Efficiency | Heat Output | Lifespan (use hours) |
| HPS | Medium | High | ~24,000 |
| MH | Low | High | ~24,000 |
| CMH | Medium | High | ~24,000 |
Light Emitting Diodes (LED)
LED grow lights are the newest technology on the market and are quickly taking over as the most used grow light both recreationally and professionally. This is because LEDs are extremely efficient and, while their upfront cost is higher than other systems, they last longer, they are more efficient with electricity, they produce a full light spectrum, they are easy to set up, they don’t produce a lot of excess heat, and they are extremely reliable.
The major drawback to LEDs is that there is no industry standard for how they are constructed so craftsmanship and quality can vary widely.
T5 Fluorescent
You’re probably already familiar with fluorescent bulbs – they are often used in office spaces – but you may not know that they are also very popular for growing indoors. They use low energy and have a long lifespan but their light output is a white-blue color and the intensity and temperature are too low for any plant that is not a low-light plant. They are excellent for starting seeds and early vegetative growth but they often cannot keep up with the needs of plants as they grow larger.
| Light Type | Pros | Cons |
| HPS | · Produce a lot of light
· Industry standard · Cheap start-up cost · Excellent results · Dimmable · Excellent flower production |
· Require more electricity and is less energy efficient than other options
· Requires excellent airflow and ventilation · Emits a lot of temperature, controlling temperature in a space can be difficult · Higher cost in the long run · Requires a reflector and ballast · Decent lifespan but brightness dims over time |
| MH | · Great for seedling and vegetative growth
· Produces a lot of usable light · Very cheap to purchase and operate · Dimmable |
· Requires a reflector and ballast
· Decent lifespan but brightness dims over time · Poor results during flowering · Weaker performance than HPS or LED bulbs · Requires a ballast and reflector to operate · Coverage area can be weak |
| CMH | · Last twice as long as HPS or MH
· Burn hotter and create light closer to natural sunlight · Produce sufficient light to support vegetative and flowering growth · Dimmable |
· Requires a ballast and reflector
· Still relatively expensive when compared to HPS and MH bulbs · Emits more UV light than other bulbs meaning growers need to wear long-sleeved shirts and sunglasses · Brightness dims over time · High temperatures can be difficult to control and can damage plants |
| LED | · Energy efficient and produce more light per watt than HID or T5 (usually)
· Operate at lower temperatures · Longer lasting than other lights · Full spectrum that can be fine-tuned for different growth stages · Dimmable · Cheaper to operate · Can be plugged directly into a wall outlet · Can be entirely automated · Easiest to grow with requiring no extra equipment |
· Expensive initial cost
· Cheap LEDs can cut corners on performance · Sometimes not strong enough for flowering · No reflector included · No industry standardization so quality can vary wildly |
| T5 | · Less expensive than other grow lights
· Great for low-light plants · Great coverage area · Last longer than other grow lights · Low operation temperatures |
· Can only be used for specific situations like low-light plants or for seedlings
· Are not useful for flowering · Are not useful for vegetative |
How Far Should Seedlings Be from a Grow Light?
This is a great question that has a few different answers because it depends on the kind of light and the stage of growth your plant is in. Think of a flashlight again: when the light is closer to a surface, the ring of light is small, but the brightness is more intense. When you pull the light away from the wall, the coverage area grows larger, but the light intensity grows weaker.
Ideally, we would like intense coverage over a large area, but this is only possible with very high-end equipment, so we need to find a balance between the two and a couple of factors play into this: heat produced by the light, brightness, and stage of plant growth.
Take a look at the following chart for guidance. Keep in mind, these numbers are general reference points
| Light | Nearest distance (inches) | Furthest distance (inches) | Seedling height (inches) | Vegetative height (inches) | Flowering height (inches) |
| 100W LED | 12 | 24 | 16-24 | 10-16 | 12-16 |
| 200W LED | 12 | 36 | 24-36 | 16-24 | 12-16 |
| 300W LED | 12 | 36 | 24-36 | 16-24 | 12-16 |
| 400W LED | 12 | 36 | 24-36 | 16-24 | 12-16 |
| 1200W LED | 18 | 46 | 32-46 | 24-36 | 18-28 |
| HPS | 24 | 60 | 48-60 | 36-48 | 24-36 |
| MH | 24 | 60 | 48-60 | 36-48 | 24-36 |
| CMH | 24 | 60 | 48-60 | 36-48 | 24-36 |
| T5 | 6 | 18 | 12-18 | 6-12 | 6-10 |
How to Hang a Grow Light?
Hanging a grow light is easy and most grow lights come with the equipment to set everything up. Be aware that HID and T5 bulbs are just that, light bulbs, so you’ll need to get a ballast and a reflector before you are able to use your light. With LEDs, you can simply hang them and then plug them in.
Regardless, the process of setting up your lights is simple – VIVOSUN includes rope rachet hangers with every light so set up is simple.
Step 1: Gather your supplies.
Step 2: Hook the metal hangers (if included) to your light. Next, connect the carabiners on the rope rachet hangers to the hoops on the metal hangers.
Step 3: Hang the long end of the rope hanger on the cross bars, loop it over the bars, and connect it to the rope.
How Long Should a Grow Light Be On?
The grow light on and off cycle is called the “photoperiod.” Your photoperiod is going to vary depending on the type of plant you are growing but you can assume that all plants need periods of darkness to utilize the sugars, amino acids, and building blocks by sending them to the appropriate place, just like a child needs enough sleep to grow.
Let’s break down what a good photoperiod is for certain plants, like cannabis, based on the stage of growth.
| Stage of growth | Time on (hours) | Time off (hours) |
| Germination | 16 | 8 |
| Seedling | 18 | 6 |
| Vegetative | 18 | 6 |
| Flowering | 12 | 12 |
As you can see, the flowering stage has a notably longer off period. This is because, like most flowering plants, cannabis reacts to light changes in the natural environment to stimulate the production of flowers and fruits. Just as the amount of available light changes during the year, you should change the amount of light available to your plant as it matures to encourage flowering.
How Much Is a Grow Light
The price of a grow light can vary wildly especially when you add in the cost of extra equipment like reflectors and ballasts. Let’s take a quick look at the average price range for various grow lights. Be aware, as the light becomes more powerful (higher wattage), the price will go up.
| Light type | General price range (dollars) |
| LED board | $70 – $500 |
| LED bars | $150 – $500 |
| HPS bulb | $10 – $30 |
| HPS bulb + reflector + ballast | $150 – $300 |
| MH bulb | $10 – $30 |
| MH bulb + reflector + ballast | $150 – $300 |
| CMH bulb | $50 – $80 |
| CMH + reflector + ballast | $150 – $300 |
| T5 bulb | $20 – $40 |
| T5 bulb + reflector + ballast | $70 – $200 |
What Is the Best Grow Light for Indoor Plants
When you ask the question “Which grow light is best” for indoor growing, you’ll get a ton of different answers. A better way to get to the bottom of that question is to ask, “What is the best grow light for me?” If it is your first light, you’ll probably want to look into LED grow lights.
LEDs are an excellent, reliable, powerful new technology that is extremely easy to use and set up. We have a ton of guides about LED lights, so check them out here!
Factors to Consider When Choosing Grow Lights
There are a few factors we recommend when choosing your next grow light:
- Cost: Find a fixture that fits your budget. Look at your electricity bill and expect that it will rise in the coming months when you start running your grow light. HID bulbs will be more expensive to operate, LEDs will be cheap, and T5 bulbs will be very cheap. Check out our blog on the price of growing at home versus purchasing cannabis from a dispensary to see what you will save.
- Size: Your light size can be thought of in two terms: the literal size of the fixture and the wattage. The larger the size the higher the wattage, which means it will take up more space in your grow area and may be too powerful for your space. Check out our sizing chart here.
- Uniformity: Uniformity refers to the balance of the light spread as shown by a PAR map. Try to find a light that has an even PAR map, where light is not much dimmer around the edges than in the middle – the more even the light distribution the better.
- Efficiency: You’ll want an efficacy rating of around 2.5µmol/J. This shows that the fixture is quite efficient at providing light to your plants in a good spread without wasting excess energy.
We hope this long guide helps direct you to find the perfect grow light for your tent. There is a lot of information here so if you made it this far, very well done! You’re on your way to being a great grower – this is just the beginning and it’s a very exciting beginning!
If you have any questions, please don’t hesitate to reach out to us!
And be sure to check out our other blog posts for useful tips on becoming a great grower!
Subscribe to the VIVOSUN newsletter for growing tips, grower stories, and special offers, and get 12% off your first order!
We love the new VIVOSUN Smart Grow System and we are certain that you too will love it once you try it.
And join our Facebook farmer’s community for even more exclusive contests and prizes!
Download VIVOSUN App to get 18% off and explore more information!
