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 does not provide many definitive answers even after hours of looking. As aspiring expert horticulturists, we have now spent a great deal of time researching LED grow lights in the hope of answering the question of whether we should all be using this latest tech in all of our gardening endeavours. 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 we have trying to make head or tail of this mountain of information (and disinformation!), we created this website to summarise our 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 lamps 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.
Types of LED grow lights
LED grow lights come in all shapes and sizes and as the technology evolves and more companies and organisations get into the business of growing plants under LED plant lights, the variety of LED grow lighting is becoming increasingly diverse so categorising the different types in this rapidly changing landscape can be a challenge. To begin with, a few different competing LED packaging technologies exist in today’s grow lights, these include:
In addition to these different LED packaging technologies, LED grow lights also come in a variety of form factors including:
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 nanometers (nm). So for instance, 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, maximise 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), our first instinct as to which is better for plant growth will typically be 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 lighting, 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 plant 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:
Clearly 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. We 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 us 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. So 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 we 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 us that they have a role to play in the plant - so shouldn't they be included?
Anyway, the bottom line is that you can't 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? 😉
Until someone comes up with a 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, we're 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.
Other advantages of LED grow lights?
Another important advantage of LED lights for plants 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 lamps, far less heat is produced and this provides us with some other important advantages:
So, we don't know about you but we're 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...