Why Are Grow Lights Purple? (And Are “Blurple” LEDs Effective?)
Last updated February 29, 2020 By Steven 12 Comments
Only LED grow lights are purple. And only some.
Why are they purple?
Well, technically they aren’t.
The light appears purple due to the differently colored diodes in use: mainly blue and red. This pinkish/purplish glow has also been dubbed “blurple”, a term that is often used in a somewhat derogatory way these days.
Because many of the earliest LED grow lights, especially the low quality ones from China, emitted a “blurple” light. And people who bought those lights got burned.
They ended up with a light that couldn’t grow a blade of grass and understandably developed a negative impressions of purple lights.
Is that impressions justified? Yes and no.
We’ll get into that a bit more below. First we’ll go into more detail on why these grow lights look purple.
Why Are LED Grow Lights Purple?
LED grow lights have multiple diodes that each emit a single color of light. Some have only white diodes, while others have diodes in various different colors. It is the combination of those colors that creates the light we see.
Fixtures that emit a purple light contain a large amount of red and blue diodes. The smaller the ratio of red to blue, the more purple the light looks. The larger the ratio, the more pink it appears.
Since red wavelengths are the most important for plant growth and plants like a ratio of around 5 to 1 of red to blue light, most LED grow lights actually contain more red than blue diodes. This means that their light is actually more pinkish than purplish. It is the “blurple” light I mentioned above.
Why Do LED Grow Lights Use Mainly Red And Blue Diodes?
Plants use mostly red and blue light for photosynthesis. They use about 5 times as much red light as blue, and far more of either than any other color.
Many LED manufacturers took this knowledge and constructed grow lights featuring nothing but red and blue diodes.
They said that using white diodes would mean lots of light in other wavelengths like green and yellow, which plants don’t use. You would essentially be paying for electricity to create light that just goes to waste.
With only red and blue diodes, all of the electricity is used to create light that plants absorb and turn into energy. That is why their LED fixtures had only blue and red (and sometimes a few white) diodes.
Or so they claimed.
In actuality, they used mainly red and blue diodes, because they are easier and cheaper to make.
But consumers bought into the “red and blue light only is best” myth. At one point, it was very hard to find lights that were not mostly red and blue.
So why do I call it a myth? Is red and blue light bad?
No, it isn’t. It works just fine. But it is not ideal.
Are Purple LED Grow Lights Effective?
Purple LED lights work. They veg and flower plants well.
But more and more, we are coming to the realization that full spectrum white light is better for plants. It turns out that, while plants don’t use green or yellow light as much during photosynthesis, they do make use of some.
Besides, sunlight is white light that contains all colors of the spectrum. And sunlight has been growing plants since long before humans ever even walked the earth.
HID lighting hasn’t been used for growing quite that long, but it has been in use for decades. And it is also white light.
Metal halide bulbs emit cooler white light, with higher amounts of blue, while HPS bulbs emit a warmer white light, with much more yellow, orange and red.
Both do not contain all colors in similar amounts, like sunlight, but both are still white light. Newer ceramic metal halide bulbs come much closer to natural sunlight, containing a very similar spectrum.
The light from white LED diodes also contains a spectrum similar to sunlight and CMH bulbs. Both white LEDs and CMH bulbs are much more effective at growing and flowering plants than LED fixtures with only red and blue diodes.
But there is an even better spectrum for plants than this.
What Color Spectrum Is Better Than Purple?
As mentioned, plants want light in every color of the spectrum. But they want more blue and even more red, than any of the other colors. Thus, it stands to reason that the best light for plants contains all colors, but contains an extra heavy dose of red, and more blue than other colors, but less than red.
And that is the ideal spectrum. Almost.
Adding in a bit of UV and IR light has been shown to improve yield qualities, so having some light in the UV and IR wavelengths is even better. Learn more about the best color lights for plants here and about the effect UV light has on them here.
In short, what we want is a spectrum like the one shown in the chart above. One with light in every color, but a large peak on red and a smaller peak on blue. In addition, small tails that extend from the blue side into the UV wavelengths and from the red side into the IR wavelengths.
How Do We Get This Ideal Spectrum?
These days, there are a lot of LED grow lights that provide the ideal spectrum. But there are only a handful that do it efficiently and also sell for a reasonable price.
Black Dog lights, for example, have a great spectrum. But have you seen their pricing? The Phytomax-2 1000 costs over $2000!
It is possible to get the same great spectrum while spending far less. Let’s look at some of those lights.
Many people swear by HLG grow lights. Most of their fixtures have all-white diodes. Two of their fixtures add in some deep red.
They are much cheaper than Black Dog, but still cost quite a bit more than Chinese brands (HLG lights are made in China, but the company is American). Read my review of HLG grow lights.
Mars Hydro’s newest lights also use all white diodes and some of their new fixtures also combine those with deep red diodes. They are very similar to HLG lights, but with a much lower cost. Read my review of the Mars TS and SP fixtures.
The main difference is that HLG uses Samsung chips, while Mars uses lower quality Epistar chips. For budget lights with the higher quality Samsung LED diodes, check out my Spider Farm quantum LED review.
Neither of those options have UV light and only the ones with far red diodes have IR light, but only a small amount. To get both UV and IR, along with all colors and peaks on the red and blue, your best bet are COB LEDs.
I have a rundown of the best COB LED grow lights here and another one of the best full-spectrum white LED grow lights. Both feature the Phlizon COB series of lights as the number one pick.
The Phlizon lights have full-spectrum white COB LEDs, plus additional diodes that provide red, blue, UV and IR light. In short: they have the perfect spectrum for all stages of plant growth and are especially great at flowering.
COB LEDs have taken the growing world by storm. Not only have a great white light spectrum, but they are also incredibly intense and achieve a much deeper canopy penetration than other LED diodes. I’ve written a whole article on why COBs are great for plants.
For years, Amare were the only good provider of COB LEDs. They still are a good provider, but they are expensive. Optic LED then came along and sold very similar lights for less. But they are also still expensive.
Phlizon sells fixtures that are virtually identical to the Optic lights, but cost half the price. That is why I recommend them in both of the article mentioned above. Read my review of the Phlizon COB fixtures here for more.Do you know why many LED grow lights give off a purple light? I explain the reason and also tell you why these purple lights are not as good as you were led to believe.
Make the Most of Your LEDs: 5 Tips for Cannabis LED Growing
The growing prominence of LED grow lights in the cannabis community is undeniable. So we have put together a few tips for anyone wanting to give them a go.
With LED technology rapidly advancing in recent years, more cannabis growers are now switching to LED for their indoor operations. Merely a novelty just a few years back, LED grow lights are now performing as well, if not better, than HID lamps, and have also become more affordable. Due to the many advantages of LEDs, from consuming less energy to being more robust and having a longer life span, they are now a great choice for indoor cultivators of different skill levels. If you grow cannabis with LEDs or plan to make the switch, here are some tips for you.
WHAT TO LOOK FOR WHEN CHOOSING AN LED GROW LIGHT
Before you go buying an LED grow light, it helps to know what’s available. Currently, there are three main types of LEDs that you can use to grow cannabis, each of which has its pros and cons. The type of LED light you should choose will depend on what exactly you’re looking for, and how much money you’re willing to spend.
3 MAIN TYPES OF LED GROW LIGHTS
- STANDARD (“PURPLE”) LED
These standard LED light fixtures were the first type available for growing, and today, they’re still widely available. These lights contain a lot, sometimes hundreds, of small to medium wattage LEDs (3–5 watts per single LED) in a compact fixture. Cannabis growers sometimes refer to these as “purple” lights, as they often comprise a mix of red and blue LEDs that combine to emit a purple hue.
The biggest advantage of these standard LED lights is their price point. Most are manufactured overseas, and you can find them aplenty on eBay and other places online. A disadvantage is that their quality is often lacking; they can be less than reliable, and their light output is often lower than other types of LEDs, leading to lower yields. To remedy this, we’re now seeing standard LEDs begin to include COB LED lights or UV LEDs in addition to the red and blue, which can help with yield and bud quality.
These standard LED light fixtures were the first type available for growing, and today, they’re still widely available. These lights contain a lot, sometimes hundreds, of small to medium wattage LEDs (3–5 watts per single LED) in a compact fixture. Cannabis growers sometimes refer to these as “purple” lights, as they often comprise a mix of red and blue LEDs that combine to emit a purple hue. The biggest advantage of these standard LED lights is their price point. Most are manufactured overseas, and you can find them aplenty on eBay and other places online. A disadvantage is that their quality is often lacking; they can be less than reliable, and their light output is often lower than other types of LEDs, leading to lower yields. To remedy this, we’re now seeing standard LEDs begin to include COB LED lights or UV LEDs in addition to the red and blue, which can help with yield and bud quality.
COB means “chip on board”. A COB LED is made of many hundreds of tiny LEDs on one single small chip, as opposed to differently coloured LEDs spread over the entire fixture (as is the case above). COBs are among the most efficient LEDs. They produce a very intense white light that is similar to the natural light spectrum of the sun. One advantage of COBs is that they have good penetration into the plant canopy due to their intensity, resulting in a final yield approaching that of quality HID lamps. They also have a light spectrum that is optimal for healthy growth, and are very energy-efficient.
The drawback can be that a quality grow light with COB LEDs is quite expensive compared to cheaper purple lights. Some grow light manufacturers combine several COB LEDs into one fixture, often equipping them with lenses and reflectors. There are also lights available that are comprised of only one single COB. These single-COB fixtures can be a good choice for larger growing spaces, as you can space a number of them evenly for light distribution across the entire area. Most growers use COB LEDs with a light spectrum that works both for vegging and flowering, but you can also find those with a spectrum (“colour temperature”) tuned specifically to vegging or flowering.
COB means “chip on board”. A COB LED is made of many hundreds of tiny LEDs on one single small chip, as opposed to differently coloured LEDs spread over the entire fixture (as is the case above). COBs are among the most efficient LEDs. They produce a very intense white light that is similar to the natural light spectrum of the sun. One advantage of COBs is that they have good penetration into the plant canopy due to their intensity, resulting in a final yield approaching that of quality HID lamps. They also have a light spectrum that is optimal for healthy growth, and are very energy-efficient. The drawback can be that a quality grow light with COB LEDs is quite expensive compared to cheaper purple lights. Some grow light manufacturers combine several COB LEDs into one fixture, often equipping them with lenses and reflectors. There are also lights available that are comprised of only one single COB. These single-COB fixtures can be a good choice for larger growing spaces, as you can space a number of them evenly for light distribution across the entire area. Most growers use COB LEDs with a light spectrum that works both for vegging and flowering, but you can also find those with a spectrum (“colour temperature”) tuned specifically to vegging or flowering.
Spread-style LEDs are comprised of a large number of small LEDs that are spread out on a larger panel or board. There are also spider-style LEDs and rack-style LED lights, which are widely used in commercial greenhouses. The spider-style LED lights don’t use flat panels, but spider-like “arms” with LEDs instead.The main advantage of spread-style grow lights is that they are among the most energy-efficient LEDs, which means you can get the most light for the wattage you’re using. A disadvantage is that quality spread-style LEDs, such as the spider-style lights, can be extremely expensive.
Spread-style LEDs are comprised of a large number of small LEDs that are spread out on a larger panel or board. There are also spider-style LEDs and rack-style LED lights, which are widely used in commercial greenhouses. The spider-style LED lights don’t use flat panels, but spider-like “arms” with LEDs instead. The main advantage of spread-style grow lights is that they are among the most energy-efficient LEDs, which means you can get the most light for the wattage you’re using. A disadvantage is that quality spread-style LEDs, such as the spider-style lights, can be extremely expensive.
THE ADVANTAGES OF GROWING WITH LED LIGHTS
We’ve already mentioned that LED lights have several advantages when compared to other types of grow lights, such as HID. Here is a full rundown of why you may want to choose LEDs for your next growing operation.
1. LED LIGHTS ARE MORE ENERGY-EFFICIENT
Compared to HID lights, LEDs are a lot more energy-efficient. They use less electricity, and will cost much less to operate in the long-run. Although high-end LED lights can sometimes cost a good chunk of money outright, the investment is almost always worth it as your savings over time will make up for the higher initial cost. Likewise, quality LED light fixtures will also have a longer life span compared to HID, the latter of which tends to lose performance over time and needs frequent replacement. A good LED light can last you many years with no maintenance needed.
2. THEY RUN COOL
LEDs produce a lot less heat compared to HID lights, which can be a big advantage as you won’t require extra cooling systems in your grow room or tent to keep temperatures optimal. This is especially advantageous if you grow in summer or happen to live in a warmer climate. The downside to this is that if you live somewhere cold, you may now need to consider a heater in the colder months. But as LEDs save you money over time, this can make up for the potential costs of running a heater.
3. WITH LED, YOU CAN MOVE YOUR PLANTS CLOSER TO THE LIGHT
LEDs produce less heat, which means less stress on your plants—so you can move your lights closer to your plants without any negative effects. Higher light intensity translates to higher yields!
4. LED LIGHTS REDUCE YOUR WATERING SCHEDULE
With less heat produced by lights, the soil in your pots will stay moist for longer, thus reducing the amount of times you need to water. If you’ve just switched from HID to LED and are used to your plants drinking quite a lot, you now need to be careful with your new watering schedule under LED, otherwise you might overwater your ladies.
5. YOU NEED LESS NUTRIENTS
When you water cannabis plants, you’ll normally do so with an infusion of nutrients. In addition to watering less, your plants will also need less nutes than they would before. In addition to some nice savings on nutrients, the less-frequent watering and feeding schedule will also decrease nutrient buildup, so there’s a lower risk of nutrient lockout and plant deficiencies.
GROWING WITH LED: WHAT TO CONSIDER FOR EACH STAGE OF CULTIVATION
As we touched on earlier, many types of LEDs have a fixed light spectrum that works for both the vegetative (growing) and flowering phases of cannabis. This way, you can just use the same light throughout your entire grow from seed until harvest.
Although this is convenient for most, there are those who want to fine-tune their lights for best results and optimal efficiency in each growing phase. For this purpose, some commercial LED lights have a switch to activate a veg light spectrum or a flower light spectrum. Here are some more factors to consider throughout each stage of growth.
A) LED LIGHTS AND SEEDLINGS
As soon as your seeds have sprouted, your soon-to-be cannabis plant will need light to grow. Compared to more mature plants, however, your seedling is much more sensitive to intense light. Because of that, you should be careful when starting out with strong LEDs.
If your LED has a dimming option, turn your light to a lower intensity. If this isn’t an option, consider moving your lights further up, away from the seedling. On the other hand, ensure that you do not move the lights too far up, as this could cause the seedling to grow spindly and lanky.
Likewise, if your LED has a switch to activate either a vegging or flowering spectrum, set it to veg, where the light normally emits a “cooler” blueish light, which is optimal for this stage. Set your timer to 18 hours of light per day, with 6 hours of darkness.
As your seedling grows taller, stronger, and approaches the most robust part of the vegetative growing stage, you can then gradually increase the light intensity.
B) LED LIGHTS DURING VEGETATION
Set your light to 18 hours per day and 6 hours of darkness. Some growers choose to grow with 20–24 hours of light to maximise vegetative growth.
Monitor your plant’s development; if all goes well, it should grow healthy, strong, and bushy. If it grows lanky and spindly instead, this is likely because your plant is not getting enough light. Increase the intensity by lowering the light toward the plant canopy or turning up the intensity using the dimmer if your light has one.
How long you want to veg your plant will normally depend on how much space you have available. You can technically let your plant grow under 18–24 hours of light as long as you want, but there will likely come a time when you want to switch to flowering, as the plant would otherwise simply grow too big. Know that some cannabis strains can stretch considerably (up to 2x or more) during early flowering. Take this into account upon deciding when to initiate the switch to bloom.
C) LED LIGHTS FOR FLOWERING
Photoperiodic cannabis starts to flower in late summer when the daylight hours naturally begin to diminish. Indoors, the grower is responsible for inducing bloom by setting the light schedule to 12 hours of light and 12 hours total darkness. If your LED light has a flowering switch, turn it to flowering mode.
When you flower indoors on a 12-12 schedule, it is important that the 12 hours of darkness are not interrupted. So make sure that your tent or greenhouse doesn’t have any light coming in from outside. This would otherwise revert your flowering plant back to veg or potentially cause other issues such as hermaphroditism.
If your LED has a dimmer, now is the time to turn your light to its maximum intensity, or lower your light to the recommended distance from your plants for the flowering stage. If you are not sure what this distance is, most grow light producers have recommendations available.
Important: if you change anything with your lights, such as when you increase intensity and/or lower their position, make sure to do so gradually over several days, rather than in one go. Too sudden of a change can stress your plants too much.
AUTOFLOWERS AND LED
If you’re growing autoflowers rather than photoperiodic strains, you don’t need to bother with initiating flowering by switching your lights to 12 hours on/off. You can just leave your autoflowers at 18–24 hours of light per day up until harvest. Then again, if your LED light has a flowering switch, you should still use it once your autoflowering cannabis is in bloom. This will help increase yield.
LED COMPARED TO HID GROW LIGHTS
HID lights, such as MH/HPS grow lamps, are still widely used as they are cheaper than good LEDs, yet are still reliable for growing top-quality weed. Furthermore, grow tent kits often include HID lights, so many new growers start out with these, rather than LEDs. If you’re wondering now whether you should switch to LED, here are some more aspects to think about.
WHAT IS YOUR BUDGET?
Although you can get LED grow lights “for cheap” nowadays, many of these budget versions from overseas are not worth the money you’d save outright from avoiding high-quality fixtures. If you want quality LEDs, you will normally need to spend some good money to get a light that promises good yields and will last you a long time. So if you’re on a budget and don’t want to, or can’t, spend a lot, it makes sense to continue with HID for the time being, rather than settling for a cheap LED. HID lights will still do a splendid job supporting growth and flowering—in fact, they can still outshine a decent amount of LEDs when it comes to performance.
HEAT PRODUCED BY HID LAMPS CAN BE A PRO OR CON
As already mentioned, HID lamps produce a large amount of heat. So, if heat in your grow room is a concern, you definitely want to look into LEDs. This can save you additional money on exhaust and cooling systems. On the other hand, if you grow in a cold environment, you may just want to stick with your HIDs as they keep the grow room cosy for your plants without needing additional heating.
WHICH LIGHT GROWS BETTER (AND MORE) BUDS?
Are there any differences in bud quality and yield with LEDs compared to MH HID lights? Some growers say that MH lamps give better yields or “prettier buds” compared to LEDs. But there are also those who say that, although HID might give you better yields, LED lights make for a better taste and/or overall better quality of weed. Obviously, what is really “better” is open to interpretation.
For additional information on how LEDs compare to other types of grow lights, you can also read our article on the pros and cons of different types of lights for cannabis.
HOW TO AVOID PROBLEMS WHEN GROWING WITH LED
Modern LED grow lights, for example COB lights, can emit light that is as intense as that from HID. If your plants are too close to your LEDs, this can lead to “light burn”, with discoloured or bleached leaves, nutrient deficiencies, and all sorts of growing troubles. Because of this, it is important to keep your LEDs the proper distance away from your cannabis plants.
There is no “one size fits all” recommendation for the right distance for all types of LEDs, since this varies greatly by type. It depends on the amount of light your LED is emitting, whether your lamp also uses lenses or reflectors, and so on. The manufacturer of your lights should clue you in to the recommended lamp distance from the canopy, either on the instructions that come with your lights or on their website. As a general rule, however, most LEDs should be about 30–45cm away from the tops of your plants to support healthy and vigorous growth.Making the switch to LED grow lights can be as intimidating as it is exciting. Here are 5 tips all new LED growers should know. ]]>