Choosing the right grow light involves a lot of research so we put together this comparison between the different types of grow lights we’ve tried and look at the quality of light they produce. Factors such as the shape and size of your space, and the spectrum you want, and your ideal start-up and operating costs are all factors you can take into account when deciding which of these is best for your situation. (It’s probably LED)
Rather than comparing specific models within a category, we’re comparing the different lighting categories themselves. We also don’t go too in depth with spectral analyses so this article is more of an overview if you’re getting started. None of the links are affiliate links, and most importantly we’re not sponsored by any brand, so this is just an unbiased look at the tools we’ve come across over the years.
Grow lights in question
The lights we tend to use are in the lower-medium range in terms of strength and output, typically ranging from 100W-400W power draw. Wattage is often used as a rough gauge on the strength of a light, but when you consider the variety of efficiencies of different set ups (such as LED arrays with a high output per-watt), their strength won’t always be well reflected by wattage figures. It’s a bit like rating a car’s horsepower by how much gas it consumes. If you’re looking for high-power grow light comparisons you can check out higher strength arrays but we’ll leave that up to the experts on lighting and yield!
Grow Light Types
Comparison Setup
The lights are all set on the same plinth 24″ from the wall, and a 36″ ruler is attached to the wall to get an idea of the distance of the fade, rate of fade, warmth and coverage. Each photo is shot with the same settings to ensure that the brightness, warmth, and tint of each light is true in comparison without the auto white balance undoing the natural color of the light. Shot from the same distance at 125/sec, 400 ISO, f8, and 4800K, M+1 to balance for our studio.
While we made efforts to stabilize the setup, it’s mostly just to see the light quality with an idea of scale. Coverage and light quality varies per brand and model so these pictures and notes aren’t to be taken as gospel, more detailed information should be available for each specific light on their websites.
LED Grow Lights
LEDs are the most modern option of this collection, running cooler and producing higher output per watt than older generations of lights while consuming less electricity. They can produce a more optimized light spectrum too so the wavelengths of light are better tuned to match the needs of plants. LEDs are also known to last a lot longer compared to other lighting types.
Where HPS bulbs shout, LEDs sing
Dr. Bruce Bugby of Utah State University argues that the traditional measure of Photosynthetically Active Radiation or PAR excludes some wavelengths that support photosynthesis:
“Wavelengths are synergistic. The best analogy I can use is a balanced diet,” says Bugbee. He explains that a robust component of various wavelengths both within and outside of PAR allows greater rates of photosynthesis than narrow-band spectra, achieving an effect that’s greater than the sum of the parts. “You have to have all the nutrients for proper growth.”
Redefining the McCree Curve at Utah State University
The ability to create arrays of multiple diodes means you can construct lights that produce a more balanced spectrum for your plants. You can read more about the lighting metrics PAR, PPF, and PPFD here.
That said, LEDs can cost more up-front. Most companies on the market use diodes from other manufacturers for their lights and assemble them onto boards with drivers, heat sinks, casings etc. One way to sift through them is to find the brand of diode in their product description; CREE and Samsung are two manufacturers to look for since they produce some of the most efficient LEDs for agricultural production. Because of this, it’s really the configuration of LEDs and the housing hardware that makes the difference between LEDs.
So let’s take a look at a few archetypes:
https://siliconlightworks.com/resoures/what-are-cob-leds
https://www.samsung.com/led/lighting/applications/horticulture-lighting/
https://fluence.science/redefining-the-mccree-curve-at-utah-state-university/
https://fluence.science/science-articles/horticulture-lighting-metrics/
LED Bar Light
This HLG bar light is the most recent addition to our collection. It’s a 4 foot bar-shaped array of white LEDs with red diodes every few inches. Because it’s less than 2 inches wide and not even an inch tall it’s great for a long, narrow grow space like a cabinet. Their narrow profiles and passive cooling makes these a discreet, low maintenance lighting solution for small to medium sized plants. LED bar lights often come in 2 ft, 3 ft and 4 ft options, but common dimensions can be found on Samsung’s website.
We just finished our first grow using this light and it produced nice resinous flowers that are frostier than we’ve seen with HIDs. LED bar lights tend to be less powerful than full size arrays, and are often used as supplementary lighting or side lighting in larger grows. HLG recommends using 2 of these for a 4’x2′ space but because we’re growing small bonsai in a 4’x1′ space, one seems to be enough per cabinet. If you’re going for a large yield you can consider adding more bars in your setup or upsizing to a full-size array.
In terms of light quality this bar produces a soft, diffused, almost ‘smooth’, slightly warm white light. 244 white Samsung LM301B diodes are supplemented by 10 Deep Red diodes that deepen the spectrum. The metal bar runs warm but not too hot to hold on to, so you can get the light close to the ceiling of your grow area if need be, and handle it comfortably.
https://www.samsung.com/led/lighting/led-modules/industrial-light-module
https://www.ledgrowlightsdepot.com/products/horticulture-lighting-group-hlg-saber-100
https://horticulturelightinggroup.com/products/hlg-saber-100w
Read more about our DIY grow box cabinet build with the HLG here!
LED COB Spotlight
COBs are a single chip that are technically arrays of diodes. They’re often positioned behind a convex lens to project light directionally like a spotlight. In this case we have the Optic 1 by OpticLED, which is powered by a single CREE XLamp CXB3590 COB. You can also switch the lenses out for ones with different angles to control the range of coverage.
We found these lights to be surprisingly powerful at just 54 watt power draw, projecting a strong, slightly warm light with a sharp edge. The light produced by a single point can feel a bit harsh or “dry”, by creating hard shadows with sharp edges and less ambient light. While it doesn’t have multiple diodes dedicated to higher and lower ends of the spectrum (like deep red and UV), the ‘full spectrum’ 3500k option is still well rounded.
These require a bit more distance than bar lights due to the concentrated beam, so they work well in tall square spaces like closets or tents. Like the HLG, these are often used as supplementary lighting in larger operations, and as they don’t need a fan, they’re also noiseless. One thing to consider if you’re using this as your main light, is that it has a circular profile and can create dark spaces in corners. These tend to run a bit warmer than the bar light but are still cool enough to hold which is definitely a plus for COBs with oversized heatsinks.
https://cree-led.com/media/documents/ds-CXB3590.pdf
LED mixed-diode array
An LED array is technically a configuration or arrangement of multiple diodes which allows LEDs of different spectrums to be mounted together, optimizing the wavelengths to best supports photosynthesis.
We powered our larger grow tent with this mixed LED array, the Optic 2 (gen4). It contains a total of 88 diodes, with two of them being the same large COBs seen in the Optic 1: the CREE CXB3590, and the rest being a pretty diverse variety of single spectrum diodes.
COBs:
1xCREE XLampCXB3590 Cool White
1x CREE XLampCXB3590 Warm White
Bloom Enhancers:
72x Samsung LM301H (3500k)
8x CREE XPE Deep Red (660nm)
4x CREE XPE Royal Blue (460nm)
1x Ultra Violet
1x Infrared
This light is great for a medium sized grow space, light quality is fantastic, and it’s one of the more powerful lights we have at the moment. The diversity of the diodes in the Bloom Enhancer portion is highly nutritious and then COBs add some muscle to the mix. Its dimension and coverage is reminiscent of the HID/hood combination, producing a rectangular area of coverage. At the time we had a ton of ventilation and flowered under the COB + Bloom Enhancers at 80% and the leaves had a beautiful bluish-green iridescence with frosty colas.
As for the hardware itself, it’s a metal housing construction with sturdy dimmer knobs and separate heavy switches for the COBs and the enhancers. The housing itself doesn’t get hot at all, though the internal fans make a tiny bit of noise.
The Optic 2 offers more control than the COB only light, with dimmers and switches enabling you to control brightness or switch between COB-only and COB + enhancers. Another big plus for this type of light is that it’s great for both vegetative phases and flower because these bloom enhancers can be turned on when in flower to adjust your plants changing needs as resin production picks up. One of the CREE COBs is slightly warmer than the other, the difference slightly noticeable in the top two photos; the side left of the ruler a bit cooler than the right side.
OpticLED assembles these from components, so the configurations are key. The housing, dimmers, drivers, heat dissipation, spectrum quality, even reaching outside the visible light spectrum with the Infrared and UV diodes are all major pros to consider for this type of light. If we were in a slightly larger space we would be running this as our main light. Mixed LED arrays can be found for less as well by other brands, but the quality can vary quite a bit so it’s worth at least looking the maker of the diodes.
HID (High Intensity Discharge grow lights)
HIDs are a slightly older technology than LED, often referred to as being part of a different, previous, generation. HID refers to a class of bulbs known as High Intensity Discharge lights, including Metal Halide and High-pressure Sodium bulbs.
The light spectrums that HIDs produce are good but not quite as well tuned as LED, offer lower efficiency, and produce lots of heat. That said, they can be quite powerful, and the startup costs are low compared to LED setups. Where an LED could run around $250 to $500, a MH or HPS bulb and hood can cost as little as $100-150. The electricity cost is something worth considering, because HIDs draw considerably more energy for the same output. We grew with the HID for a few years with our bigger bonsai before recently switching to LEDs.
Metal Halide Bulb (MH)
Metal-halide bulbs have a spectrum which is slightly better for the vegetative phase, with its cooler white spectrum. Feels like daylight without being too harsh, and the spread is quite soft.
While we used MH and HPS for a few years, we found that the bulbs are fragile, get piping hot, can break and even release mercury. That said, the startup cost of a MH/HPS setup tends to be pretty affordable and still works well in many situations.
High Pressure Sodium Bulb (HPS)
Another bulb that works interchangeably with metal-halide bulbs is the HPS, the high-pressure sodium bulb. Because this bulb has a slightly warmer spectrum with a bias toward the lower end, it’s ideal for the flowering stage. It is often used in tandem with the metal-halide bulbs, with the vegetative phase being driven by the cooler white MH and flowering by the HPS.
These are common practices and not necessarily rules though of course, you can technically flower with just one type of bulb. HPS have the same drawbacks around heat, fragility and efficiency, and both bulbs will benefit from annual replacements for around 20-30 dollars.
Personally I found the ‘daylight’ white Metal Halide to be more liveable than the HPS, in the sense that it feels more like you’re outdoors rather than in a grow room. Overall the fact that the bulbs are interchangeable is helpful and the cost being so low makes HPS, and HIDs in general still worth considering.
Fluorescent Grow Light
Not quite an ideal spectrum but fluorescent grow bulbs are accessible and easy to start up. These are usually rather low power, but when they’re put together in numbers they can throw some light. Often you’ll find these strung together in small houseplant nurseries powering tropical plants.
While they don’t generate too much heat and allow lower wattages, this light doesn’t quite have the output necessary for much agricultural output. Most importantly I think is that the tube is loaded with mercury – it’s not even that they break often, it’s that you’re constantly worried about breaking this long thin tube of glass. Overall fluorescents are not quite ideal but will still grow plants, and while you can grow cannabonsai with these, they’ll likely end up thinner and longer than preferred due to low-light induced stretching.
Amazon ‘Blurple’ bulb
These lights are often advertised and recommended by Amazon, and unfortunately I think a lot of people think it’s just a casual purple color. It’s actually so vivid it leaves you completely disoriented. Instant headache! Even if the plants liked this type of light much, there are other options that don’t cause pain, so save yourself the trouble!
Our Grow Light Recommendation
So there are a lot of things to consider when picking a light, and hopefully this series has helped with giving some basic information around the lighting types and some of their characteristics!
We’d recommend an LED array or a mixed diode bar light if you’re going to be growing for a few years. It’s worth the investment and the plants will thank you! If you’re just experimenting and know you won’t be for very long, the HPS/MH bulb HID set up may be the best if you’ve got the space for it!
