What Is Lux and Why Is It Important?


What Is Lux and Why Is It Important?

Understanding how measurements of lumens may impact growers’ choices when it comes to lighting is relatively easy. The chart below outlines bulb types and brightness to give growers a better idea of what to expect.

As noted above, lux is a measurement of how much visible light falls on a surface. It is measured as a product of lumens per square meter. Lux is arguably a more important metric for growers since it defines the amount of light that actually reaches a plant canopy instead of the brightness emitted from the light source.

It’s common to see measurements listed in either or both lux and lumens. Unfortunately, these units only measure visible light. That is, the spectrum of light that humans can perceive with their eyes – not the full spectrum of light that plants require to grow and thrive. That’s measured in PAR.

How Is PAR Quantified and Why Is It Important?

PAR, short for photosynthetic active radiation and sometimes referred to as PAR photon irradiance, is the best tool for understanding how light intensity and spectra influence plant growth.

Unlike lux and lumens, it is not technically a metric or a measurement. It defines the spectral range of a light and is usually measured in energy units (W/m2), although some scientists, botanists, and light manufacturers still use einstein units.

PAR can be measured most accurately using a spectroradiometer. If growers have the chance to evaluate spectroradiometer patterns produced by the light manufacturer, a third-party testing facility, or an unrelated scientific experiment, they should definitely do so. Look for irregular patterns and note that these may be indicative of insufficient light intensity in certain spectra.

It’s worth noting here that some color spectra within the visible light range are more useful to plants than others. It’s also worth noting that the ends of the PAR extend beyond the visible spectrum.

While humans can only see light with wavelengths between 380 and 750 nm, plants can benefit from light wavelengths extending up to 780 nm. Wavelengths above 750 nm produce infrared light, but the fact that growers can’t see its effects doesn’t mean it’s not important. Thankfully, even the most efficient of grow lights still produce sufficient infrared light to supply plants with everything they need from that end of the spectrum.

When evaluating what grow lights to use, look for a light that offers a wavelength range that covers the entire PAR spectrum (400 nm to 700 nm) but emphasizes the red and blue wavelength ranges. Experienced growers may want to focus on different wavelengths of light within this spectrum, depending on their growing goals and what types of plants they are cultivating.

For those just getting started with indoor setups, it’s best to look for a light that offers customizable wavelength capabilities. This lets growers tailor the light regimens for their plants as they learn more about what each species or strain needs. LED lights are a great choice since many high-end models are fully customizable. That means growers can provide plants in the vegetative stage with more blue light, then switch over to increased levels of red light during the flowering stage.

What Are Watts and Why Are They Important?

Watts don’t measure light intensity or spectra at all. Instead, they measure rates of power use. This is relevant to growers because manufacturers often use wattage as a proxy for describing a light’s power capability. Don’t just assume that higher wattage means a stronger light, though, because efficiency tends to increase as wattage decreases. LED lights are a perfect example of this. Their efficiency is influenced by design features and quality of components, and one of the things growers like most about them is that they don’t consume much power. That doesn’t mean they don’t produce plenty of light.

The lumens produced per watt of power by LEDs are almost always higher than other types of bulbs.

However, LED lights are especially prone to reductions in efficiency as they increase in wattage. That’s because the semiconductor circuit board that contains the LEDs heats up when it is exposed to more power, and higher temperatures can cause significant decreases in efficiency.

Bonus Metric: Day Length / Rated Life

The rated life of a lighting system may not affect how well the fixtures and bulbs perform on a daily basis, but it can definitely have an impact on growers’ budgets. Some types of grow lights boast rated lifetimes of over 10 years, while others will only last between three and five years. Keep factors like the day-length, or how often the lights are switched on each day, in mind when evaluating rated lifetimes of different lights.

4. Budget

In an ideal world, no grower would have to settle for less efficient or less effective lights as a result of budget concerns. Not everyone has a ton of expendable cash to put into setting up a new system, though, so budget still belongs near the top of any reasonable list of considerations. The good news is that there are plenty of options available at all price points. The bad news is that the grow lights that require the smallest initial investment often come with hidden costs.


CFL bulbs are usually the cheapest option. Growers can usually find single bulbs for less than $10. They’re not designed explicitly for growing plants, which means there won’t be any helpful features like the ability to customize the light spectrum or turn them on and off automatically according to the plants’ schedules, but they’ll do in a pinch.


Growers who have less than $100 to spend per light but don’t want to settle for regular CFL bulbs can find T5, T8, and T12 fluorescent grow lights within their price range. They’ll need to buy a few of them to grow any amount of food or flowers but the system should still be able to pay itself off within a few years.


LED lights tend to be more expensive than their fluorescent counterparts, but they’re worth the money. LED light systems designed for growing indoors have all the features growers need to control light intensity and PAR, which can be a huge asset in even small-scale grow rooms. They’re also more energy-efficient than CFLs, so while LEDs require a larger initial investment, they’re better able to pay for themselves over time.

HPS lights sometimes fall into this price category, as well, but only the small-sized lights. Specialized HPS grow lights should still have plenty of features, but they’re less energy efficient than LEDs.


Heavy-duty commercial systems often feature HID lights. Most use a combination of HPS and MH fixtures. These systems can cost well over $1,000, and since they feature lights with higher heat outputs, they require ventilation, air filtration, and indoor climate control. The cost of running HID light systems can be quite expensive, so it doesn’t make sense for novice growers looking to start moving their operations indoors for the first time to invest in this kind of system.

There are also some high-quality LED systems that fall into the higher price range. They are a better fit for home growers who have the extra money in their budgets for professional-grade equipment. Since LED lights produce very little heat, there’s often no need for extensive support systems with multiple fans, ventilation points, and environmental controls. This makes getting started growing indoors much simpler, to say nothing of budget concerns.

5. Vendor Quality

Even with a particular price point, not all grow lights are equal. To complicate matters further, not all vendors are equally reputable. That means the technical specs for a product may not be accurately portrayed in marketing materials, which can create some serious problems for growers who are relying on their new equipment to perform as advertised. Some lights are less powerful than their manufacturers’ claims would indicate, while others have shorter rated lifespans or produce a narrower spectrum of light.

Given that grow lights can be quite expensive, it’s essential that even novice growers do their due diligence when it comes to evaluating vendors. Issues like overstated or inconsistent wattage and the potential for premature failures can wind up costing growers tons of time and hundreds, or even thousands, of dollars. Investigating a company to ensure that its products are sound and its business practices are beyond reproach takes far less time and ensures that money invested into grow lights will be well spent.

How to Evaluate Vendor Reputation

The first thing to do is to check the vendor’s website. If it looks anything less than 100% professional, consider that a warning sign. Make sure the website offers plenty of information about the company, including a phone number that customers can call for support, a physical business address, and information about the vendor’s shipping, warranty, and return policies.

Be wary of any vendor that offers deals online that seem too good to be true. While buying lights from a reputable vendor online can help growers save money, it’s better to trust a domestic company that sells only high-quality brands than it is to go on a discount site and look for lights made in China and sold by random online merchants. Scams are common in all industries, and this one is no exception.

Don’t just assume all the information on a company’s website is accurate. Turn to third-party review sites, forums, or local friends and family members for advice, and check with the Better Business Bureau regarding customer complaints. Investigating a company’s reputation only takes a little time and it can save consumers a lot of money and endless headaches.

Brands to Look For

Most vendors source their products from at least a few manufacturers. Try to find one that only sells high-quality, name-brand lights and accessories. Here are a few well-respected brands to look for:

  • Fluence produces a wide array of lights and lighting products designed explicitly for indoor commercial growers. This Austin-based business has been producing high-quality products since 2013 and is well known for its Ray, SPYDR, and VYPR series lights.
  • Gavita Horticultural Lighting produces LED lights and accessories for customers ranging from huge commercial growers to novice home growers who just need a single light fixture. The company has been in business since 2010 and have developed a good reputation for its products.
  • Iluminar manufactures some of the highest quality grow lights available. They can also manufacture custom projects for their customers.
  • NextLight produces products ranging from small-scale LED systems to large commercial systems. They also manufacture LED accessories.
  • Optic LED provides indoor growers with LED lights designed specifically for indoor cultivation. Their products are popular among small-scale growers.

What to Avoid

No matter how tempting it may be, don’t rely on sites like Alibaba for grow lights. It’s fine to check reviews and ratings on Amazon but buy directly from reputable vendors. It gives consumers the chance to speak directly with a customer service representative who can provide accurate specs and answer questions and ensures that they will get the right products. Merchants on Alibaba and similar sites practice drop shipping, which means they never even see the products they sell, and are known for sending customers cheap knock-off products. When deals look like they’re too good to be true, it’s usually because they are.

6. Common Grow Light Accessories

The easiest way for growers who haven’t yet familiarized themselves with indoor growing practices to ensure that they’ll get everything they need to set their lights up and start using them immediately is to buy a grow light kit. Kits come with not just the lights, but also all the accessories required to set them up and run them. Once they know their way around lighting and accessories, growers can purchase individual lights and separate accessories to customize their systems, but unless they’re willing to devote a lot of time to learning new skills, kits are a much better option for those just getting started.

What You Need to Know About Grow Light Kits

The best way to figure out what’s available for grow light kits is to contact a vendor directly. Each kit is a little different, so it’s difficult to make generalizations. As a general rule, though, top-end kits come with these accessories at a minimum:

  • Fans and/or filters
  • Grow tents
  • Ducts and clamps

Buying Separate Accessories

Want to buy high-quality grow lights then create a customized system? For those with experience in the field of lighting installation, this may be an option. Here are a few of the most essential accessories to look for:

  • Ballasts are used to regulate the power supply to grow lights. Prefabricated kits almost always come with ballasts, as do many specialized grow lights designed specifically for indoor cultivation. Those who are purchasing individual bulbs or tubes made by generalized manufacturers will need to buy these essential components separately.
  • Grow tents make it easier to create a controlled environment in spaces that were not explicitly designed for indoor horticulture. They often come included with more expensive systems, but they can also be purchased separately or even replicated more cheaply by especially handy growers. Grow tents make it easier to control everything from temperature to moisture levels, which protects both plants and growers’ indoor spaces, so they’re worth the money.
  • Ducts and clamps are used to ensure that the grow tent is sealed. They also make it easier to keep wiring organized.
  • Fans and Filters play several important roles in an indoor grow. Fans help to ensure proper airflow, reduce residual heat from lights with high heat outputs to create a steady temperature, and improve the air quality in a grow room or grow tent. High-quality filters will also remove contaminants and help to control unwanted odors.

Whether growers choose to purchase prefabricated kits complete with tents, fans, ducts, and ventilation systems or create their own systems using separate lights and accessories, they are better off buying high-quality products instead of cutting corners. It’s the best way to ensure that everything will run as intended, which is essential given that the plants will rely exclusively on artificial lighting to grow and thrive.

7. Know the Unit Economics (Cost to Light Per Unit Area)

No matter what kind of equipment they use and on what scale, growers need to understand unit economics. Unit economics can be understood in the context of grow lights as the ongoing cost of lighting a particular area. For commercial growers, understanding unit economics also requires balancing the cost of operating a lighting system against the potential profits produced by the crop. For now, let’s just take a look at the ongoing costs of operations.

Understanding the Unit Economics of Grow Lights

Understanding the unit economics of a particular grow light requires two pieces of information: the local cost of electricity and the power draw of the light system.

Growers need to find out how much they pay for electricity. They can find this out by asking their utility providers, who will provide information about electrical costs as a product of centers per kilowatt-hour (kWhr). Bear in mind that the cost of running a grow light extends slightly beyond the base kWhr price of electricity. Providers always tack on fees and taxes, which usually amount to around 50% of the kWhr price of power. That means if the company says it charges $0.08/kWhr, consumers are likely paying more like $0.12/kWhr.

Determining the wattage of the bulbs is a little easier. This information should be available on the manufacturer’s technical spec sheet and on the lights themselves. Remember to multiply the wattage of a single light by the number of lights in the array to get the total power consumption of the system.

To determine the unit economics of the system as a whole, divide the wattage by 1,000 to accommodate for the fact that electricity prices are provided in kilowatt-hours, not watt-hours, then multiply it by the cost of electricity per kWhr.

Example #1

Feeling confused? Let’s take a look at an example that might be applicable in a very small-scale grow room or tent:

  • You buy four 40w CFL bulbs for a new grow. Multiply 40w by 4 to get 160w of total power consumption for the system, then divide this number by 1,000 to get the total power consumption in kWhr of 0.16 kWhr.
  • Your cost of electricity is $0.10 kWhr after taxes and fees. Multiply that by 0.16 kWhr to get $0.016/kWhr.
  • This equation, which can be expressed as (40x4)/1000 x 0.10 = 0.016, will give growers the approximate cost of running their lights for one hour.

To get an accurate idea of the cost of running the system throughout the growing season, growers will have to determine what light schedule they will be using and approximately how long it will take for their crops to grow. For the sake of simplicity, let’s extend the above example under the assumption that growers will be using their lights 24/7. Although few crops require round-the-clock lighting, assuming constant use gives growers an idea of what to expect under the most intense usage scenario.

  • Take the hourly cost of $0.016 required to run the setup for one hour and multiply it by 24 to get a daily cost of $0.384. It will cost roughly 38 cents to run the lights for one full day.
  • Multiply $0.384 by the length of the growing season to get the overall power consumption required to grow the crops. Most crops require a growing season of at least 90 days, so let’s assume that everything goes smoothly and growers are cultivating short-season crops. This gives an equation of $0.384 x 90 = $34.56.

This may sound like a great deal, but it’s important to note that 160 watts of power won’t produce sufficient lumens to cover any reasonable growing area. This setup would be fine for a very small-scale grower just experimenting with indoor cultivation for the first time, but it certainly wouldn’t provide sufficient light for a commercial grow, or even a large-scale home grow.

Example #2

Home growers who are looking to get more serious about their operations often purchase LED grow lights, which typically offer the highest lumen-to-watt ratio. To use a real-world scenario that would actually be applicable for more serious growers, let’s take a look at the unit economics of the Fluence SPYDERx PLUS. This light is designed to cover a 4’ x 4’ area and delivers an average of 1030 µmol/m2/s of uniform light. It takes 660w to run but is large enough to cover a small grow room without additional lighting. Let’s use the above formula to determine how much it would cost to run the SPYDERx Plus through one growing season.

  • Divide 660w by 1,000 to get 0.66 kWhr.
  • Multiply 0.66 kWhr by $0.10 to get $0.066/kWhr.
  • Multiply $0.066/kWhr by 24 to get a daily power consumption rate of $1.584.
  • Multiply $1.584 by 90 to get a seasonal operational cost of $142.56.

The difference in unit economics is huge, but so is the efficiency of the lighting system. Growers who are serious about producing decent crops indoors will find that the first example doesn’t provide sufficient light, while the latter one will allow their plants to grow and thrive. A basic understanding of unit economics is the first step toward determining operational costs.

8. Scalability

Many novice indoor growers purchase their first light arrays with the intention of expanding their farming or horticultural operations from there. When this is the case, scalability becomes a serious concern. The right lights will improve unit economics and allow growers to create efficient modular systems as they scale their operations up, but not all grow lights are created equal from a scalability perspective.

There are two factors to consider when evaluating the scalability of a lighting system. First, growers should ask themselves how the system will perform from a cost perspective as they scale up their operations. Second, they should determine how the lights they choose will affect yields as they begin producing more crops. Let’s break down how each of the three main lighting types performs on both of these levels.

CFL Lights and Scalability

CFL lights are used primarily by small-scale home growers. They don’t scale well from either a cost perspective or a yield perspective and will need to be replaced with commercial-grade lighting if growers get serious about their operations.

CFL lights have a low output compared to other options, so growers need to use more than one of them. They also need to be placed closer to the plants in order to work. These problems are counterbalanced by the fact that they’re inexpensive, work in almost any standard light fixture, and come in various color temperatures. Small-scale growers who don’t plan on expanding their operations or don’t mind investing in new equipment if they do can start out with CFL lights, but no serious grower would use them.

HID Lights and Scalability

HID is considered one of the best options for commercial-scale indoor growing. These high-quality lights are less expensive than other options with comparable light outputs, and they produce great results. They scale well as long as growers are willing to invest in accessory equipment like fans and ventilation.

HID lights produce a lot of light, but they also produce a lot of heat. This means they must be placed much farther away from the plants and they must be outfitted with special hoods and ballasts. They also require specialized sockets and have relatively short lifespans. Growers who invest in HID lights may feel stuck with them since they require so much specialized gear, which means they’ll also be stuck with the disadvantages of excess heat production and frequent bulb replacement.

LED Lights and Scalability

LED offers the best scalability of any type of grow light. LEDs are energy efficient, produce next to no heat, plug into standard outlets, and have long lifespans. They’re also powerful enough to cover large areas. The only real downside to LEDs is that they cost more than CFL and HID lights. As technology continues its march toward progress, though, they are quickly becoming more affordable.


When it comes to scalability, LEDs are the best way to go. They can be used in small-scale home grows and large commercial grows, alike, which means those who develop a passion for indoor growing can purchase more lights without having to scrap the systems they already have in place.

9. Safety

Some grow lights create more safety risks than others. There are two factors that influence the safety of a light: its fragility, and what materials it uses. LEDs also have a clear advantage in this category. Here’s why:

They’re Less Fragile

LEDs are less likely to break when jostled or even when knocked down. This makes them relatively safe even in household grows where pets, children, or careless adults may disturb the lights once in a while. Unlike other options like fluorescent tubes or HPS lights, they won’t shatter or explode, even if they’re knocked over with significant force.

They Have a Low Risk of Causing Fires

Contrary to popular belief, most of the fires started by grow lights aren’t caused by excessive heat output. They’re usually electrical fires. HID lights are far more likely than LEDs to cause fires since they require specialized wiring and large, 220V “dryer” outlets. Not all growers know how to safely and efficiently perform electrical work, which means those who use HID lights without adequate experience are more likely to experience electrical fires.

They Contain No Mercury

Most high-quality grow lights contain mercury, which can pose a serious health hazard to growers and their families if the lights break. LEDs contain no mercury. That means even if they break while people are in the grow room, there’s no need to worry about exposure to this dangerous toxin.

The Exception to the Rule

Any grow lights can create a perfect environment for mold if growers aren’t careful. That’s because turning the lights on and off alters the moisture levels in the room, leading it to condense when the lights aren’t on. Since LEDs don’t produce as much heat, it takes longer for the excess moisture to evaporate, even when they are on. This is one of the few areas in which LEDs do not perform noticeably better than their alternatives.

10. Purpose

Before purchasing grow lights, newcomers to indoor cultivation should stop to give some thought to exactly what they’re trying to do. Defining the purpose of the grow room will narrow down options and clarify which of the factors discussed above should be prioritized when making a final decision. Growers should ask themselves the following questions:

  • Do I want to grow commercially? If so, LEDs and HID lights are the best options.
  • Is growing just my new hobby? When this is the case, CFLs or smaller LEDs will do the trick.
  • Do I need to optimize yields? Those who want to produce maximum yields in small spaces should restrict their options to HID lights or high-end LEDs.
  • How large is my budget? If it’s extremely small, invest in some CFLs for now and upgrade the light array later.

There’s no one right answer to the question of which grow lights are the best since every indoor grower has different intentions. Answering these purpose-driven questions will give growers a better idea of how to evaluate the information presented above in reference to their unique situations.

11. Miscellaneous Helpful Notes & FAQs on Grow Lights

Choosing a light array is one of the hardest parts of setting up an indoor grow, but that doesn’t mean growers who have already evaluated their options and made their choices are off the hook entirely. There are a few things they’ll need to keep in mind if they want to get great results.

10 Mistakes to Avoid Once You Buy Grow Lights

  • Burning the plants
  • Providing insufficient lighting
  • Using the wrong light spectrum
  • Choosing the wrong light schedule
  • Not adjusting the height of the lights as the plants grow
  • Failure to provide proper maintenance
  • Using low-quality LEDs
  • Placing the lights at the wrong distance from the canopy
  • Overwatering the plants when switching to LEDs
  • Failing to consider all the factors when buying lights

Most of aspiring indoor growers’ questions should already have been covered above. There are a few more things some people think about before purchasing lights, though.

Can You Use “White” Household LED Lights to Grow Plants?

Household LEDs are cheaper than specialized grow lights, but they don’t emit a full light spectrum. In fact, they typically emit less than 30% of the PAR required for growing plants indoors. Just buy the grow lights.

Grow Lights in Greenhouses

If you live some place with a short growing season, supplementing direct sunlight in a greenhouse with artificial lighting is a great idea. It allows growers to experiment with plants that require longer growing seasons without having to invest in new, fully enclosed some place grow rooms. Just try to stick with less than 20-40 watts of light per square foot and make sure to provide supplemental heating to accommodate plants from warmer climates.

How Long Should Grow Lights Be Left On?

There’s no universal answer to this question. As a rule, most plants need 12-16 hours of light per day, but some plants can benefit from 24-hour lighting. It’s best to research each plant’s needs under normal, outdoor conditions where the plant thrives, then try to replicate them.

What Type of Light Is Best for Growing Plants Indoors?

Almost any kind of light can be used to grow plants indoors, but the options discussed above are much better than incandescent bulbs. For more in-depth details on why, re-read the article.

Can Any Light Be Used as a Grow Light?

Technically, yes. However, anyone but experimental growers are better off buying specialized grow lights. They’re designed to provide a full PAR spectrum to ensure that plants get all the wavelengths they need to grow and thrive during different stages of development.

Other Helpful Notes and Tips

Still want more information? Here are a few last notes and tips that can help growers get started:

  • Grow lights aren’t as powerful as the sun, so they need to be run for longer. Timers can help growers manage their light cycles appropriately.
  • Fluorescent bulb and tube manufacturers don’t include information about color temperature on their packaging. Instead, they categorize the bulbs into categories like “warm glow” and “daylight.” This makes it hard to use normal fluorescent lights not designed for indoor growing.
  • Always buy ballasts that have reflectors to increase the efficiency of the light array.
  • Around 2/3 of your lighting budget should be spent on fixtures. Only 1/3 should go to bulbs
  • Most non-commercial growers can expect a high-quality lighting system to have a payback period of between one and three years.
  • Anyone can grow plants indoors. It just takes research, practice, and the right equipment. Those who have come this far and are ready to purchase their first lighting arrays are already well on their way to producing high yields of quality crops, so buy the lights and get growing!
  • The Bottom Line

If it seems like choosing the right grow light is a difficult process, that’s because it is. There are tons of options out there, but they’re not all created equal. Whether they plan to grow a few plants in a closet or eventually scale up to a full warehouse setup, growers should take the time to review the differences in products described above and find the ones that provide the best fit for their needs, goals, and budgets. When in doubt, don’t hesitate to ask a reputable light manufacturer or an expert in the field for help.

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