LED Grow Lights (or is it L.E.D. Grow Lights!): The Facts


There is a ton of information on the web and lots of academic studies looking at the use of LED grow lights for plant growth but a lot of it is confusing and had not really given me many definitive answers after a couple of hours of looking. As an aspiring horticulturist, I have now spent a great deal of time reading and researching LED grow lights in the hope of answering the question of whether I too should be using this latest tech. There are bound to be lots of you out there asking the same question, and so you don’t spend (waste?) as much time as I did trying to make head or tail of this mountain of information (and disinformation!), I created this website to summarise my findings and to answer questions from an amateur gardener’s point of view.

First off, what are LED grow lights?

For the totally uninitiated, light-emitting diodes (LEDs) are the same little lights that you find on everyday electronics, so for example, the pinpoint of light flickering away on this laptop (or is it an old-fashioned desktop?) that shows that it is alive and kicking or that the hard drive is working, is an LED. The LEDs used in LED grow lights are essentially the same as these but they are much more powerful and a bunch of them are grouped together into a single fixture to provide plants with enough light for them to grow.

Are LED grow lights better than other light sources?

Well, before we can answer that question, we have to know a little bit more about light itself. Without delving too deeply into the physics, light waves come in an array of different colours each with its own unique wavelength that is measured in nanometres (nm). So for Image of the colour spectrum of visible lightinstance, blue light might have a wavelength of 430nm or red light might be 660nm. Even different shades of the same colour have their own precise wavelengths within the range for that colour, so a deep red would be something like 700nm, whereas a lighter shade of red might be 640nm. Unlike conventional electric lighting which emits a range of colours simultaneously (combining to form the final white light product that we see), an LED essentially only emits light of one particular wavelength (in reality, it actually emits a very narrow band of wavelengths, but for our purposes, we can think of it as emitting only at its designated wavelength). Combining LEDs of different wavelengths into a single light fixture gives us the power to precisely control the colours of light that plants are exposed to, and in so doing, maximize exposure of our plants to light that promotes optimal growth, or that’s the theory anyway!

LED grow lights vs sunlight

Since plants have evolved over millions of years to grow in sunlight (which consists of the whole spectrum of visible light plus ultraviolet and other non-visible wavelengths), my first instinct as to which is better for plant growth, as I am sure yours will be, is to vouch for sunlight. What could be better than beautifully natural sunlight stimulating our plants to grow? But before we dismiss the idea of human-made Image of the sun against a blue skylighting, we should acknowledge that there is some evidence where one might argue that nature is not as optimally designed as it might first appear. There have been studies that have suggested that too much light (and in particular the yellow colour wavelengths) can start to stress plants out and inhibit their growth by suppressing chlorophyll formation. Since we are pretty sure that plants don’t use every wavelength of light within sunlight and some wavelengths may even be inhibitory, this raises the question of what happens if we were to remove those undesired wavelengths. Is it possible to increase the level of growth in our plants?

Another argument in favour of us having the potential to design lighting that is ‘better’ than sunlight is that nature evolved not to please us humans, but through a Darwinian ‘fight for survival’ mechanism from the point of view of the plant. So ‘better’ growth might mean different things from a plant’s perspective than it does from ours and there might be some naturally-evolved plant processes that may be undesirable to us as plant growers. An example of this can be seen with fruit-growing, where we have become quite adept at crossing plants to produce ‘better’ varieties of fruit which do not contain seeds (for instance, seedless grapes or some types of citrus fruit). Yet the whole reason for a plant to produce fruit in the first place is as a mechanism for it to disperse its seeds – what possible use is there for a plant to have seedless fruit? – there isn’t.

Of course there are also other more practical reasons why we might not be able to grow our plants in sunlight, like we may not have the space to grow them outside in the first place or we may not want to expose them to the possibility of pests and diseases. Alternatively, we may live in a place that is often overcast (sound familiar?) or where the outside conditions are unsuitable for the type of plants that we would like to rear.

Irrespective of our reasoning for growing plants under electric lighting, the problem we currently face is that scientists are a long way from fully understanding all the complicated systems and processes that go on in a plant in response to sunlight, and for that reason, given the choice between trusting a couple of hundred years of scientific endeavour versus millions of years of evolution, it’s really a no-brainer. So when choosing indoor lighting, we should try to stay as faithful as possible to the structure of sunlight, and we can use our current knowledge of what photosensitive pigments are found in plants as a guide to determining the wavelengths of light that are required for optimal plant growth, even if we don’t yet fully understand what all their functions are.

LED grow lights vs other lighting systems

Are LED grow lights better than other electric lighting systems? The answer to this question is a bit clearer. There are several factors to account for when comparing lighting systems – below is a comparison of the electrical properties of different light sources:
Table comparing the life expectancy and electrical efficiency of different lighting technologies
Bart chart comparing the life expectancy of different lighting technologiesClearly LED grow lights have a huge advantage in how long they last, and more importantly, they are far more electrically efficient i.e. they use a lot less electricity, which should be good news for our electricity bills. I did initially start out with a table comparing the energy and cost differences one might expect to achieve with the different grow lighting systems, but it proved to be too unreliable primarily because trying to get an answer as to what are equivalent grow lamps between one system and the next (for example HID vs CFL grow lights) appears insurmountable to me at the moment. The problem is that different lighting systems inherently emit different wavelengths of light with plants using some of them and ignoring others. So you can’t just compare the Lumens or the Lux (measuring brightness) between lamp types because although you might be able to match them in terms of brightness, the individual wavelengths themselves and the usefulness of the light itself to the plants will vary.

So you might think, ok, we should be comparing the photosynthetically-active radiation or PAR emitted from each light type. To measure PAR we appear to need to know the Photosynthetic Photon Flux Density (PPFD) in µmol/m2/sec of each type of light. Damn, can they make it more complicated!? So that means the number of photons (think light particles) that hit one square metre of plant surface each second. That’s better. But this still does not address the problem of the differing wavelengths. Please correct me if I am wrong, but let’s say that you have the required amount of PAR for your type of plants, say 400 µmol /m2/sec. If all 400µmoles of that photosynthetically-active light is of the same wavelength, let’s say 660nm of red light, then surely that is not comparable to another type of light that is emitting the same 400µmoles of light particles but of 430nm blue light!? Clearly, the two different types of light are both photosynthetically-active radiation but each is going to have very different effects on plants since different plant pigments will be activated. Also, just on a more technical note, another beef I have with PAR is that it has been defined to include photosynthetically active wavelengths only between 400nm and 700nm! What about UV light (below 400nm) and far-red wavelengths above 700nm? It is pretty clear to me that they have a role to play in the plant – so shouldn’t they be included?

Anyway, the bottom line is that you cant really compare lamps emitting different wavelengths unless you break down the number of particles of each photosynthetically-active wavelength and compare their levels individually. So who is up to the task? 😉 Seriously guys, I could be missing something so if I’m not making sense then please let me know…but try and keep it as simple as possible for this simple-mined person please!

Until someone comes up with a better explanation, or better method for comparing lighting systems, trying to compare the costs of running each type of lamp in any meaningful way seems impossible right now. Instead, we need to move to a more empirical method where we should be trying to get plants to grow identically under different lighting systems in order to identify ‘equivalence’ between the lighting systems. Pretty inaccurate, I’m sure you will agree, but probably the best method that is available right now if we really want to know which system costs more to run. So I plan to begin experimenting in the future, so stay tuned…

Other advantages of LED grow lights?

LED grow lights are not in heat

Another important advantage of LED grow lights over other lighting systems is to do with the level of heat that they emit. The reduced electrical efficiency of other lighting systems really comes down to the fact that they waste a lot more of their energy producing waste heat…and so they get very hot. With LED grow lighting, far less heat is produced and this provides us with some other important advantages:

  • plants can be placed closer to light sources thereby using the available light as efficiently as possible.
  • plants tend to transpire less when it is cooler and therefore end up using less water overall.
  • plants tend to slow down growth as they approach lamps that contain blue light and it is possible to get their growth to stop within an inch of the grow light. This provides for an exquisitely simple control mechanism for plant size without doing anything other than deciding the height at which the grow lights are positioned. Practically, this can be achieved with LED grow lights, but not so with other lamps (assuming they emit blue-light in the first place) where the excessive heat emitted can damage plants when they grow too close.


  • LED grow lights do not require ballasts. What’s a ballast I hear you say. A ballast is some additional circuitry (usually in a bulky box) that is required in conventional grow lighting to prevent it from destroying itself. Ballasts use power to perform their function and this is another reason why conventional lighting is more costly to run.
  • With conventional lighting systems, we have limited control over what wavelengths of light they produce without using additional filters. Filters are inefficient, provide us with a limited ability to select desired wavelengths, and add to the cost of the lamps. The nice thing about LED lighting is that we can select the wavelengths of emitted light simply by incorporating the appropriate LEDs, so it should just be a matter of getting the perfect combination together…that is assuming that we know what that combination should be in the first place!
  • Theoretically, with LEDs, we have greater control over the intensity of light since LEDs are dimmable. Although I haven’t currently found any LED grow lights on the market that have this feature, I would not be surprised if they are produced in the near future to give us greater control over our lighting regimes.
  • and finally for the space scientist in each of us…recent evidence from NASA (who are trying to maximize the nutritional content of food for their future long-duration flight astronauts) suggests that through controlling the wavelengths of light that plants are exposed to, it is possible to increase the nutritional antioxidant content of vegetables (in this case, lettuce and radishes).



So, I don’t know about you but I’m pretty convinced that LEDs are the grow lighting system of the future (if not the present as well), but with the one caveat that we first need to know more about the lighting needs of our plants. Let’s see if we can get a better picture of that…

NEXT: what to look for in your LED grow lights…

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