HPS vs LED Grow Lights: The Spectrum Efficiency Showdown

 

The HPS vs LED grow light matchup is a clash of the titans.  Is LED more efficient than HPS?  How do we conduct the ultimate grow light review?

Growers endlessly speculate and debate which is better for plant growth. I know that you have an opinion, I certainly did!

When I stumbled upon the results of what I’m about to show you, I was completely shocked.

It went against everything I was told and read about online, which is why I am eager to share it with you.

You’re about to learn something you’re never going to forget, and your plants will thank you!

If you’re completely new to indoor LED grow lights, you might want to check out 7 Myths LED Grow Light Companies Tell You


The Spectrum Breakdown: HID Bulb vs LED Chip

 

First of all, it is no question that LEDs are more efficient at creating light than an HPS lamp.  LEDs will always beat HPS on a light meter…

But what we haven’t seen is the definitively better growth performance from LED grow lights, even at wattages that are nearly the same.  It has confused the growing community for years, and for good reason!

Some days it seems like LEDs are just… a passing and expensive fad.  Other days it looks like HPS is outdated after the next bulb swap.

You’ve seen the side-by-side grows on YouTube, however, they are often biased or just done wrong.  It is hard to put together a scientific test! There are a lot of factors to consider: temperature, distance, humidity, water, nutrients, strain, grower experience…

If we took the simple approach and put one brand of light against another, that isn’t exactly scientific, and actually, won’t tell us much.

For example, comparing the “GrowBoss 400W LED” vs the “HotDawg DE 1000W HPS” light doesn’t help us understand why or what is causing the plants to grow better.

Don’t get me wrong, comparisons are valuable, but they are quickly outdated as new technology is introduced.  Grow lights are always getting brighter and brighter…

What we need to know is what type of light is actually best for plant growth.

Am I right?

LEDs come in all sizes and colors: blue, red, purple, white, and every manufacturer claims they have created the “perfect spectrum”.  With so many conflicting marketing claims, a lot of them must be wrong and only a few right… but who?

HPS bulbs simply come in different wattage sizes.  Some HPS bulbs contain enhanced blue or other small spectrum changes, but at the end of the day, an HPS is an HPS.

Let’s face it, this is going to be a hard one to crack, so where do we turn?

SCIENCE!

 


Introducing Our Test Subject: The Tomato Plant

 

Tomato seedlings wired up with a water supply

 

The tomato plant is a fantastic test subject.  It’s commonly studied and is a good representation of the entire family of flowering & fruiting plants.

When growing a flowering plant, we want them to grow big and strong in the vegetative stage.  Plants with many big leaves and thick stems give us the power and structure needed for the flowering stage to achieve massive yields.

Got wimpy and small plants in veg?  Maybe on the tight and bushy side?  You’re going to have disappointing results come harvest time.  Plants need a robust, strong, and large structure to gain momentum for explosive growth in flower.  There is no way around it.

In fact, you should be waiting until your plant becomes a certain size and strength before flowering, so if your growth spectrum isn’t helping you achieve that goal, think of the time you are wasting!

 

Tomato Test Chamber
Tomatoes growing in a lighting test chamber from the scientific study featured in this article.

 

We will be presenting the results of an exciting scientific study that puts grow lights on a level playing field.  This research equalized technology by testing all the grow lights at the same intensity of light.

We present the results of this study done by a scientific laboratory and used wideband, narrowband, and white LEDs, some with filters to test how plants responded to different % light spectra (blue/yellow/green/red/infrared) which shows us how plants truly respond to colors, which is very exciting.

This means we rule out the many factors that change from brand to brand.  We can now focus on how efficient the spectrum of the light is to achieve growth.

A plant’s response to spectrum is timeless.  No matter how far technology advances, plants remain constant and react to light the same from day to day.

We can’t beat the sun, but when creating light ourselves with electricity, certain colors are better than others.

Identifying the best performing spectrum is a true test of efficiency that will stand the test of time…

 


The Test

32 tomato plants per light source were tested in this study, and were grafted from clones for consistency.  They were scored on dozens of criteria after 4 weeks of growth, and a few of them help us understand growth performance:

  • Leaf Area (growing power)
  • # of Leaves (growing power)
  • Fresh Weight (plant structure)
  • Dry Weight (plant structure)
  • # of Flower Buds (beginning flowering results)

We want high scores in all of these categories at the end of our vegetative cycle.  Bigger leaves, heavier stems, more flower buds = bigger harvest!

What you’ll discover is that colors and their combinations significantly affect how plants grow.  Armed with this knowledge we can grow better plants in our own homes using the latest science!

Now…on to our contenders.  If you’ve been growing for a while, I’m sure you’ll recognize these familiar faces.

 


Contestant #1: Purple LED Grow Lights

 

These “narrowband” LEDs are the oldest LED technology, developed in the 1990’s, and are still in use today.  Each LED only outputs a small range of color.

Blurple LED manufacturers claim that plants mainly use red and blue light because that is what Chlorophyll A/B pigments absorb.

These lighting fixtures use many different “LED colors” (aka multi-band) to create a wider range of light, and the spectrum will match as closely as possible the graph of Chlorophyll absorption.

Additionally, these manufacturers claim that the reason why HPS is inefficient is that it pumps out too much green and yellow light.  This makes this showdown a bit more interesting.  They’re showing a spectrum, and we’re about to see some actual results 🙂

You might also see them mention similar statements about white LED lights — that yellow/green light is not important for plant growth.

This group also holds a belief that blue is for vegetative and red is for flower.  If you have switches on your LED light, you will learn if they are doing what you actually want to your plants!

Below are two graphs from a leading purple grow light manufacturer, Kind LED Grow Lights. These claims are echoed by others in the industry.

“HPS Contains Wasted Energy” Source: Kind LED Grow Light Website – https://www.kindledgrowlights.com/pages/led-grow-light-vs-hps-grow-light
“This spectrum matches exactly the colors plants absorb” Source: Kind LED Grow Light Website – https://www.kindledgrowlights.com/pages/indoor-grow-light-spectrum-and-par-reading

 

 

Are they right?  Do plants use only red and blue light?  Are yellow and green colors wasted?

 


Contestant #2: White LED Grow Lights

 

White LEDs are increasingly popular and are becoming ubiquitous in our society.  LEDs are making their way into every corner of our world, from street lamps to flashlights.

Huge advancements in this technology allow for a very efficient LED that can produce a rainbow of colors (unlike narrowband LEDs) by using a “phosphor”.

A phosphor spreads light across many colors like a prism.  The shape and curve of the spectrum is designed to affect how our eyes perceive the color. “Kelvin” (Color Temperature) and “CRI” (Color Accuracy) are two metrics that white LEDs will always abide by.

White LEDs are created for human eyes.  The LEDs are designed to create a color that is both efficient and conforms to a Kelvin and CRI rating.  They are “locked” into certain shapes of the spectrum, so the color options are somewhat limited.

White LEDs will always try to maximize green and yellow light, because those are the colors that appear brightest to human eyes.  That’s the lot in life for most LEDs – serving humans, and not plants!

Spectrum response of white LED temperatures (source)

 

While these LEDs are not rated nor designed for plants, some growers have found that they perform well because they provide a wide spectrum of light, not only red and blue.

Manufacturers that use these LEDs often say that they are efficient because they match the “McCree PAR graph” or “fit inside the HPS graph”.

Here is a graph commonly used by white LED grow light manufacturers, this one is taken from Nextlight LED Grow Lights.  The green “line” is a white LED, the rainbow outline is the spectrum of a High-Pressure Sodium bulb.

 

“White LED is Enhanced HPS” – Source: Nextlight LED

 

Do you think white LEDs can match the growth performance of HPS?  Does the graph above even match the HPS spectrum?

Below is the famous “McCree Curve”, the version found in the original scientific paper by Dr. McCree:

 

The McCree Curve as found in – “THE ACTION SPECTRUM, ABSORPTANCE AND QUANTUM YIELD OF PHOTOSYNTHESIS IN CROP PLANTS”

 

The White LED seems to fit in the same shape as this curve and “match” it.

 

Both purple and white LED manufacturers point to valid scientific graphs relating to plants… who will win?

 


Contestant #3: High-Pressure Sodium (HPS) Grow Light

High Pressure Sodium Street Lamp
The yellow glow of High-Pressure Sodium street lamps.

 

Here comes the king! The reigning champion of grow lights. Do you think the HPS can be dethroned?

The High-Pressure Sodium bulb originated in the 1970’s and became ubiquitous in street and warehouse lighting.  The “yellow glow” was everywhere.

Someone had the grand idea of trying this bulb for plant growth, and now growers swear by the HPS.  It’s got a spectrum with plenty of yellow, red, and far-red, which is great for flowering.

How will it do in vegetative growth?  Will it stand up to the science of LED?

HPS is generally shunned for vegetative growth because of a low amount of blue, so plants can get a bit stretchy.  However, is it a myth that HPS shouldn’t be used in vegetative growth because of its spectrum?  Will plants grow lanky with a weak structure and small leaves?V

Maybe plants really don’t use green or yellow light…

 


Spectrum Composition

 

Okay!  Here are the spectrum compositions that were used in the laboratory test.

These graphs help clarify exactly the ratio of colors in each spectrum.  A specific breakdown is useful because it’s not (always) obvious when looking at a spectrum curve.

When we’re talking about photobiology, it’s important to work off of percentages and color ratios.  These are the clues we have to understand what a spectrum is doing to the plant.

What do you think? Is the red and blue spectrum optimized for Chlorophyll absorption going to pull ahead?

Is the green light in the white LED spectrum going to bog it down?

What about the little amount of blue in HPS? Are plants going to grow weak and lanky in veg?

Here we go… prepare to be surprised.

 


The Results

Are you surprised?  Remember, all of the lights were scientifically adjusted in a laboratory setting to be the same intensity in the same environment.  32 plants were used for each spectrum, which means this is a very accurate test.

Since HPS won in every category, it scores 100%.  For the other two contenders, their score is measured as a percentage of that score.  This means purple LEDs are only half as efficient and white LEDs lag by 25%.

This also means that more light from LED is needed to achieve the same results as HPS.  If you do a quick search in Google for “LED light burn”, you’ll see horror stories… this is one reason why.  More light is needed for equal results — eek!

If you’re a data person, check out the results table below:

Fresh Weight (g) Dry Weight (g) # of leaves Leaf Area (cm2) Flower Buds
Purple LED 26.5 2.3 8 724.3 2.3
White LED 48.8 3.8 9 1117.1 4.9
HPS 67.3 5.9 10 1269.6 7.3

To this day, even after analyzing this particular study for over a year, I can’t get over how spectrum caused such a difference in performance!

Different colors of light cause different characteristics to come out in plants.  There are multiple layers of biological light receptors within a plant – they are complicated, living beings that sense for light information in their environment!  It’s way cool…

Can you figure out what wavelengths were responsible for the growth changes?

And as far as performance goes,  I think you will agree that there was a clear winner.

For you HPS growers out there, it remains the king!  If you can handle taller plants in your grow setup, the HPS provided the biggest leaves, heaviest structure, and the most flower buds — a surefire winner for the vegetative growth of the tomato leading to a bountiful flowering harvest. 

Now, we might want to add a tiny bit more blue to the spectrum to help with stretching.  However, we can only do this to a point before yields start to diminish.

 

Purple LED Leaf Size
White LED Leaf Size
High-Pressure Sodium Leaf Size

Did you think that blue light would have assisted vegetative growth? Notice how that as blue light increased, the smaller the leaves became.  Less growing power!

How about that white LED?  Green light certainly seemed like it gave a  boost in the results.  This must mean there is more to know about photosynthesis than just Chlorophyll absorption.  If you’re going for LED, at least choose something that has a large amount of green or yellow light.

This spells some trouble for those of us out there who have already purchased LED systems… up to 100% more light from LED may be required to achieve the same results as HPS.  How’s that for efficiency?


Is this the end for LED?

Far from it!  If you couldn’t tell after reviewing these LED technologies, neither purple nor white was the best for plant growth.  There has to be something better out there…

… and there is.

I have a surprise for you… this scientific study also tested new, emerging LED technology.

The results are stunning.

This LED technology allows us to attain the results of HPS at the same intensity.

Check out the results below.  In some cases, HPS was outperformed…

Again, remember, we are working with the same intensity, only special colors within the spectrum are causing this massive boost in growth.

Do you have an idea of what could be causing the massive efficiency gain?

 


Two Men of Plant Science: McCree and Emerson

 

Two men made breakthrough discoveries in plant science.  Their discoveries, together, unlock secrets we can use to maximize growth in our gardens with artificial light.

 

McCree

 

The first man, Dr. McCree, observed and recorded what is known as the McCree PAR Graph:

 

The McCree Curve as found in – “THE ACTION SPECTRUM, ABSORPTANCE AND QUANTUM YIELD OF PHOTOSYNTHESIS IN CROP PLANTS”

 

Many people look at this graph and draw the conclusion that plants do not use light above 700nm.

Light in this color (above 700nm) is called “infrared light”.

The graph does show little effectiveness above 700nm…  That must mean infrared light has little to do with photosynthesis, right?

But get this:

That isn’t the right way to look at this graph.  McCree put a leaf in a special growth chamber and gave it a single wavelength, and measured the result.

So — the key thing to note is that this graph shows the effectiveness of a photon once absorbed in a plant, but it is showing the result of how a plant responds to one color at a time.

I’ll repeat this…

One color at a time.

Our collective knowledge has this fact confused, so it’s important for you to understand how to interpret this graph correctly.

May your mind think differently about plants and light after this article!

What this is telling you is that the closer light gets to red (600-700nm) the more effective it it is, which is why red is so good for plant growth.

That brings us to the part where infrared light becomes incredibly effective.

It’s almost like it has a secret power…

 

Emerson

 

Robert Emerson discovered the “Emerson Effect” in 1957.

Can you figure out the special ability that infrared light (700nm) has when it is combined with red light (680nm)?

 

That’s right, the amount of photosynthesis jumps by 50%.  Instead of 1+1 = 2…  It’s 1+1 = 3

Okay, so we really want infrared in our spectrum.

How do we do that?

Well, if you’ve read 7 Myths LED Grow Light Companies Tell You,  it’s clear that the older “narrowband” LEDs is not very efficient at creating infrared light.

Also, it’s aim is off.

See the graph above? We’re looking for light surrounding 700nm.

Infrared diodes miss the mark at 680-730nm, reducing their effectiveness to activate the Emerson Effect.

So it’s best we avoid older narrowband technology and focus on creating a continuous band of light in the red and infrared range.

This way we can pick up the full benefit of the plant photosystems (I & II) that reside at 680nm and 700nm.

What’s that technology called?

 

 

The Wideband LED

 

Our savior!

 

 

Wait a second, I’m sorry, the graph above was actually the old narrowband LED.

This LED will have the following issues, so it’s best we look for another solution for our red and infrared:

  • Low canopy penetration
  • Oversaturation of the top leaf tissue, leading to light burn
  • Limited color output, very small range

So, on to the new technology that is going to start taking over the LED game, the wideband red LED.

I hate to gush, but this type of light technology puts color right where we need it.

It’s dreamy really… Just think of the amazing plant growth you’re going to get.

Just look at all that color in the 680nm – 720nm range…  Beautiful!

 

… sweet sweet yields ahead!

Our Electric Sky LED Grow Lights adopt this new & groundbreaking technology in a special spectrum tuned for ultimate flowering plant performance.  Check them out here.

Thanks for stopping by and reading the article.  I hope you learned something.

Happy growing!

14 thoughts on “HPS vs LED Grow Lights: The Spectrum Efficiency Showdown

  1. Pingback: Electric Sky LEDs: The Next Generation of Grow Technology?

  2. Steven C Reply

    I have 3 es180’s in a 4×4 tent and all I can say is WOW. I can’t believe the growth rates. I’ve been growing for over 20 years, the last 8 years indoors so as you can imagine I have had about every kind of light imaginable. Since I started growing with these lights I have put my m/h hps 1000 and kind k5 xl 1000 into storage. Nothing comes close to these lights. Besides the fast growth rates (knocked about 2 weeks off my flower time), my yields increased by around 20 percent, and the frost… OMG, the frost on my plants is amazing. In my honest opinion, these are the best lights on the market. Way to go Dan. You knocked it out of the park.
    Customer for life.

  3. Wil F Reply

    I was skeptical about purchasing these lights since everyone claims that their lights are the best on the market. I got two ES 300’s in a 4×4. All skepticisms were put to rest as the weeks passed. The growth rates are ridiculous! I damn near grew myself right out of the tent! Light coverage is perfect. Gonna get a 5×5 next. These ES300’s will definitely be able to handle it.

  4. S Courington Reply

    I purchased the es180’s, 3 of them for my 4×4 tent and I connot believe the growth. I switched to flower earlier than I usually do and it’s a good thing because they BLEW UP in flower. My plants almost tripled in size. I have never seen growth like this.
    Thanks Dan, your lights are the best.
    Customer for life!!!

  5. SimonK Reply

    Thanks for this! Those are some interesting results. But did you forget to mention the power ratings of the light sources you tested?

    • greensunshine Post authorReply

      Hey Simon, this is referencing a scientific study, all light sources were tested in a lab setting for equal PPFD, so wattage was ruled out. Thanks for asking! This is merely a demonstration of how much spectrum is important for plant growth!

  6. Jakub Reply

    Hey, I would like to repeat the question about wattage. Could you please comment what wattage per area unit was used in each of the setups?

    With lack of this information it is actually impossible to answer the question which growing method is most [per watt] efficient, or even to compare them.

    • greensunshine Post authorReply

      Hi Jakub,

      Great question. Actually, plants don’t understand “watts” they understand light output (aka, umol/J). So this study did not consider wattage at all, it equalized the output to the same light intensity for each light source and distances: here

      Keep in mind, this study is simply showing the difference of spectrum to the plants since the lights were adjusted to equal intensity. This study is not factoring in how efficient each source is at creating light. If we wanted to understand electrical efficiency, then watts matter. When we’re simply viewing things in the eyes of the plant, only spectrum and light intensity matters.

      Hopefully this makes sense!

      Dan

  7. Shaun Reply

    This is the most bogus article I’ve ever read. LED craps all over oldschool HID lighting, outperforming it by twice the efficiency or better now. Good old 3000k spectrum LM561C diode based boards are now destroying anything an HPS could achieve, and that’s not even considering more advanced spread spectrum LED boards. Of course watts matter in this context, we want to know how much wattage was capable of growing how much plant matter. Sure you state the output was equalized, however if a luminaire only required half the energy consumption to produce that same output, then clearly you have a winner in terms of growth per watt, which is really what counts.

    • greensunshine Post authorReply

      Hi Shaun – I completely agree! LED is crushing in efficiency against HPS — even though the “spectrum” of white LED isn’t as efficient as HPS when looking at photon for photon. This matters when vetting the significance of umol/J, which LED definitely has on its side.

      Since a photon is not just a “photon”, and plants are living beings that adapt and change their growth shape, speed, and size depending on the kind of light wavelengths they receive, spectrum is important. To evaluate a spectrum (which this article focuses on), we have to rule out watts altogether.

      LED is so efficient that at this point, we reach a maximum of how much light plants can use, so have to be careful with the type of light we give our plants. If we give plants the right type of light (i.e. a better spectrum) we’ll need even less power — more points in the LED corner.

      Plants will also grow significantly differently under various types of spectrums, this is the reason why HPS definitely still has a prominent place in horticulture — especially because of the infrared output, which plants love and White LEDs don’t have. White LEDs are designed to provide the most light in the range that the human eye can see, rather than what plants can use, so exploring and learning how plants respond to a spectrum at the same intensity, which this article explores, is critical for innovation in our space.

      Thanks for the comment!

  8. James Reply

    How come there’s no spectrograph representing your full Spectrum? Every indoor grower Is looking for that perfect spectrum. Your marketing is compelling. I am on the fence. Wide band diodes I think is a big key. Two things missing in my View. Spectral control and a dimmable feature.

    • greensunshine Post authorReply

      Hi James,

      Thanks for the note! Our GS1 spectrum is patent-pending and proprietary to our brand, but it grows like nothing else on the market, and does what it says it does – bigger and faster growth! Keep in mind this light has over 50% red and 10% infrared, most white systems on the market have less than 40% red and 3% infrared. These are the key areas for photosynthesis POWER!

      We are working on a fully dimmable and easy-to-use wideband spectrum-adjustable system for growers. Stay tuned!

      Dan

  9. Dylard Reply

    I will stick with my HPS. I find the proof is in the product, efficiency and all aside. I have found that the LED grown fruit to be inferior to the HPS fruit. And yes by fruit I mean cannabis. Maybe it is different for tomatoes but if the end product is inferior I care not how much power was saved. Sorry LED lovers if I hurt your feelings. Seems like CMH (ceramic metal halide) May be a good middle ground.

    • greensunshine Post authorReply

      Hi Dylard,

      Thanks for the comment! I agree. Yes, it’s true, previous purple and white LED systems not only leave out colors that plants need, but many systems were actually just about as efficient as HPS/CMH… until about 1-2 years ago.

      This is the reason our product focuses on a wide spectrum for plants, which is what this article is about, and this product has been tested over and over by growers showing fantastic results in quantity and quality.

      All plants need is the right intensity and the right spectrum, LED is finally here and is only getting better.

      On the upside, along with saving power, you’re putting hundreds if not thousands of dollars in your pocket over years of operation of an LED system 🙂

      Dan

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