11 Core guidelines to know before buying grow lights for urban farming

Grow lights are available in an incredibly wide amount of prices, sizes, and styles.

(for a complete guide to the different types of grow lights and a discussion of their strengths and weaknesses, check out this article.)

11 Core guidelines to know before buying grow lights for urban farming

For someone just starting out with urban farming, navigating this process to buy the correct grow light(s) is not always a simple task.

Before you make a purchase decision, you may want to consider these guidelines to consider before buying grow lights: 


Skip to: 
1. Space Available
2. Heat and grow lights
3. Know the key grow light specs
4. Budget
5. Vendor Quality
6. Common grow lighting accessories
7. Know the Unit Economics (cost to light per unit area)
8. Scalability
9. Safety
10. Purpose
11. Miscellaneous Helpful Notes on grow lights


1. Space Available

 One of the most common questions beginning urban farmers ask involves managing limited space when starting an urban farming project.

If you don't have the space to operate a certain type of grow light, you won't be able to use it.

The reality is that different grow light types will require different amounts of spacing in between the bulbs and fixture and the plants. If your plants are too close to the lighting, they will at the very least have lower yield and may even literally be burned.

When space is efficiently used with grow lights, vertical farming stacks can also be feasible by creating multiple layers of plant beds and grow lights.

Do get an approximate idea of the space you will need vertically, see the tables below for LED (light emitting diode) and HPS (high pressure sodium) lighting. At the end of the day, the spacing necessary will have a lot to do with the strength of the light - the stronger the light, the more space needed is a fair rule of thumb for urban farming beginners who don't want to over-complicate planning.

LED approximate lighting distances. Source
HPS / MH approximate lighting distances. Source

2. Heat and grow lights

One of the major components of indoor growing is the temperature inside. Generally speaking, most types of grow lights will generate heat:

High Pressure Sodium / Metal Halide: will generate significant heat, must use in unison with fans or other tools for ventilation.

Fluorescent: will not generate as much heat as other grow lighting options, but still significant.

LEDs: extremely minimal heat, in most cases, you will not need to factor in any temperature differences if you are using LED grow lights.

Tip: Most content online will discuss the downsides of heat, the preventative measures required with grow lights that generate heat, and how to prevent overheating. However, for many urban farming beginners, risk of temperature becoming too low can be decreased by using a grow light that generates some heat.

Keep in mind that just because a grow light adds warmth, you will likely need to take other steps if you are growing in a particularly cold room (< 20 C or 70 F). Some options include tenting for insulation or heating pads.


3. Know the key grow light specs

Grow lights have 3 primary attributes to consider:

intensity: Lumens are a measure of a light's intensity or brightness, however this measurement is designed to quantify human visibility, not plant visibility.

The metric to consider for grow light intensity for urban agriculture is Watts (W). Generally speaking, the higher the watts, the better.

Light wattage is a key indicator of light pricing, so managing the cost-wattage trade off for your first grow light system is important.

Color: certain color spectra are better for growing plants than others. "Red" and "Blue" light spectra are ideal for plant growth, with red being associated more with the flowering stage of plant growth and blue with the vegetative stage. color is measured by wavelength (nanometers).

One of the biggest advantages of LED lighting is that it has highly customizable wavelength capabilities without changing fixtures. This results in the ability to custom-tailor the light regiment for a plant in order to create optimal qualities like flavor, texture, or even plant color.

A related metric is color temperature, measured in Kelvin (K). Keep in mind that for fluorescent CFL lights and T5,T8,T12 fluorescent tubes, color temperature will be listed on the packaging but not wavelength.

Day-length / Rated Life: A last important spec to consider is rated life of your lighting and how that coincides with not only your budget but your "day-length", or how long you are using your grow lights on a day to day basis.

While some types of grow lights have rated lifetimes of over 10 years, warranties on lights often will fall into the 3-5 year range. The durability of your light will be determined primarily by how you use it.

For example, constantly moving lights to new systems will wear down the lighting more, leaving it in the same system without much disruption may give you more usage.

As a rule of thumb, dividing the rated life by a factor of 2 is a safe precaution.


4. Budget

example cost breakdown for different TX fluorescent lighting. source

One of the most important metrics to consider when buying your first grow light is the price of the grow light.

The good news for grow lights is this: there are a lot of options at all price points.

$: CFL bulbs: can be found on amazon for less than 10 USD

$$: T5, T8, T12 fluorescent: good value for less than 100 USD. A 4 tube T5 grow light system can generate multiple hundreds of dollars worth of produce in a year (1-2 year pay back period with all other costs factored in besides lighting).

$$$: LED and High Pressure Sodium (small sizes): most LED solutions will be on the pricier side relative to fluorescent, if you are going to spend on LED's, your best option is to invest in a light from a well established LED vendor (full explanation in the next section "Vendor Quality") 

$$$$: Most heavy duty commercial style systems will involve high pressure sodium/metal halide (collectively referred to as HID or high intensity discharge)and high priced options are increasingly now appearing for LED systems. These systems will range in the thousands of dollars+ (USD) and will often be part of larger systems involving grow tents, grow "boxes", air filters, fans, controlled environment features, etc.


5. Vendor Quality

There are over 57,000 results on Amazon.com for the search term "grow lights". This vast array of options is not equal as far as quality goes.

For grow lights, ratings and reviews on sites like Amazon, Alibaba, or even niche sites for grow lights may not guarantee you are receiving the product quality you paid for.

How so? 

With grow lights, the technical specs in reality often are not as advertised, even for a brand new product.

In this case study from Albopepper.com the true wattage of brand new LED grow lights varied wildly (one light had 34.2% lower wattage than advertised).

When you are paying for grow lights, a lot of what you are paying for is wattage, so this is a serious risk to consider when buying grow lights. This sort of issue could cost you hundreds if not thousands of dollars, and, most importantly, time, if undetected.

Solution: trusted brands like Lumigrow may have more expensive products but also have a long track record of shipping consistently performing products. International products from countries like China should be reviewed thoroughly.


6. common grow light accessories

Often times a grow light will be the only part of the "package" or "kit" you are purchasing. Here are other potential additions besides the grow light that you should know about: 

ballast/fixture: grow light systems require an electrical component called a ballast to regulate the power supply in the grow light. if you are buying just a bulb, of course you will also need a ballast. this is a necessary component for lights. ballasts can be purchased independently from grow lights but grow lights can also have the ballasts incorporated into unit. 

grow tents: grow tents are another feature mainly seen with more expensive systems. Tip: It's worth noting that many of the benefits of a grow tent that help create a more controlled growing environment can be replicated cheaply DIY (not all the benefits).


7. Know the unit economics

Awareness of the cost per unit area required to light your crops is a good way to compare different grow lights and prices.

Examples for comparison:

- an 89$ T5 fluorescent 2 foot 4-tube system costs approximately $0.29 per sq inch of coverage (~304 sq inch coverage).

- 35$ LED light with $0.24 per sq inch of coverage

- $36 LED light with $0.25 per sq inch of coverage


8. Scalability

If you're planning on starting with a small growing operation but think you may eventually work up to selling your crop to restaurants, you need to keep in mind the scalability of the grow lights you are purchasing.

For example, fluorescent grow lights like T5, T8, and even T12 have been demonstrated to perform well in stacked arrangements.

Other questions to consider: 

How will the power requirements of your grow lights change at scale? 
How will the unit economic cost change?
Will I be able to effectively grow at scale with this type of grow light only? 


9. Safety

As detailed in 7 tips for vertical farming beginners, not all grow lights have the same safety risks.

Two key areas to evaluate with grow light safety are 1) how fragile the light is, and 2) the materials that are present in the light itself.

In both of these categories, LEDs have a clear advantage. For household growing projects where pets or children may be disturbing the lights, LEDs are much less likely to break when knocked down or jostled, due to the small size of the diodes and the way they are situated in the fixture.

Other lighting systems like fluorescent tubes and HPS lighting can be very fragile and will shatter or even explode if they are knocked over with enough force.

Additionally, mercury is present in fluorescent lighting while it is not present in the majority of available LED systems, if there is a broken bulb this is another safety hazard to consider, especially with children, pets, or any type of foot traffic in your growing area.

One extra consideration: HPS, Metal Halide, and even Fluorescent bulbs give off a significant amount of heat. If you are not sure you have the proper counteractive measures to mitigate this heat, not only will your plants suffer, but you may be creating a fire hazard.


10. Purpose

Take a moment to re-focus on the purpose of your grow light plans and needs now that you have read most of this article.

For a new comer, it can be tempting to buy a more complex system then necessary. One of the misconceptions about grow lighting is how little you really need to get a basic start.

Starting with a modest light set up, and making sure you have all other non-lighting aspects covered is one of the safest approaches.

With that in mind, here are some other articles to help you cheaply and quickly get started: 

> Beginner urban farming tips from Replantable, the hottest urban farming project on Kickstarter

> 3 Urban farming tools for less than 100$ beginners should know about

> Vertical farming beginner tips with Eric Amyot, CEO of modularfarms.co


11. Miscellaneous Helpful Notes on grow lights

here are a couple more tips for you, if you're still looking for more information. we will update this list and add on tips in the future: 

- fundamentally, all grow lights are replicating the sun. however grow lights are not as powerful as the sun, plan to run grow lights for 12-18 hours per day. Timers can help you manage this cycle.

- Fluorescent lights will not typically have color temperature / Kelvin rating listed on packaging in normal stores, instead they will be more loosely categorized into categories like "warm glow", "soft white", "bright white", "daylight" and "cool white" that each correspond to ratings

- When looking for fixtures / ballasts look for ones that have reflectors. Reflectors will help you significantly increase the efficiency of your lights. As an example, fluorescent lights emit light in all directions with equal intensity. Without a reflector, up to half of your light will not be shining where it needs to shine: on your crops.

- more on cost guidelines:

- Roughly 2/3 of the your grow light expense should be the fixture/ballast and 1/3 of the expense should be the bulbs. other one time costs may involved for things like mounting.
A reasonable payback period for a non-commercial grow lighting system should be around 1-3 years.