Greetings all. There are a lot of variables when it comes to cannabis grow lights, especially flowering lights. The widely accepted generality here about flowering under warmer/yellower/redder spectrums, like an HPS (High Pressure Sodium) bulb would emit, being the only way to go. I disagree. In fact, I couldn’t disagree more.
Until fairly recently I haven’t used my beloved Eye Blue Hortilux bulbs due to my aversion to the super high prices on these bulbs. Recently, I found them for about $90.00 each at GrowAce Online 400 Watt Eye Blue Metal Halide Bulb. They came fast, and I believe this is a fair price for these bulbs, considering their supreme high quality for growing/flowering cannabis.
I have been growing, mostly indoors for like 70% of the time, for just shy of a half century now—yikes. I have used a ton of different lights over that time. In today’s article, I am going to share some insights and advice on your flowering cannabis grow lights. Let’s run down some basics regarding kickass cannabis grow lights in general, then more specifically flowering lights. Now, for a bit about color temperature, in a very noncomplex fashion…
Cannabis Grow Lights: Color Temperature for Dummies
We don’t need to get all technical here at all. You simply need to know the basics. The color temperature of light (bulbs) are warmer, or cooler, in other words, redder, or bluer. You will see the word “daylight” on some bulbs, these are (cooler) bluer bulbs. Color temperature is measured in kelvins. Sunlight has a color temperature of 5,500 kelvins.
Most flowering lights are closer to 3,000 kelvins, so very “warm” or red, as far as color temperature. My very favorite flowering HID (high intensity discharge) bulbs are 6,500 kelvins (uber blue), the Eye Hortilux Blue metal halide bulbs. I know some of you guys are like “WTF?” Well, to those of you that think this is straight outta crazytown, I want to ask you, have you ever tried flowering with a bluer light? A high quality one?
While color temperature is an important factor for cannabis grow lights, another factor just as important is overall spectrum. Full spectrum bulbs are the only choice for cannabis growing in general, if you ask me. In a nutshell, you want full spectrum lights, that are as close to the color temperature (5,500 kelvins) and spectrum of the sun as possible—duh—indoor sunshine is what you are aiming for.
The Longevity of Grow Lights
In the warmer summer months, I use LED lights to flower with. I run 2 flowering tents that are 3’x3’x7’H Gorilla tents. My flowering LED lights are HLG 300 (300 watts each) full spectrum quantum boards, that are a color temperature of 4,000 kelvins. As you can see in the photo above, they work quite well. In the winter months I run HID 400-watt flowering lights; these serve as heaters and lights in the cooler ambient seasonal temps. Either Eye Blue (Hortilux), or Agrosun (Hydrofarm) metal halide bulbs are what I run.
I have had my HLG 300 LED lights for several years now without any problems, or significant reduction in lumens or spectrum. My metal halide bulbs run for just about 1 year to 15 months. Agrosun bulbs run at full output for about 11 months, and the Eye Blue bulbs run just about 14 months at full output. These times are based on a photoperiod of 12 hours on per day.
Long ago I tried some CMH bulbs (ceramic metal halide), and while I thought they worked great, they only kept full output for about 6 months before waning as far as intensity (lumens) and spectrum. I’m sure they must have come a long way by now, and while I haven’t tried them again lately, I hear good things about them from many peeps.
LED and HID Cannabis Grow Lights for Flowering
Intense, full spectrum HID cannabis grow lights that are also right around 5,500 kelvins color temperature, often fall short due to very short bulb life—at full power and full spectrum—in my experience. The 4,000 kelvin range is also sub-par in my experience when it comes to HID bulbs. The 6,500 kelvins of the Eye Blue metal halides are pretty “blue” but they work extremely well for flowering. Supreme connoisseur cannabis.
Alternately, LED lights of quality, that are in the 4,000 kelvin range and full spectrum work very well indeed. LED lights run really cool compared to HID lights, so your lighting choice should be influenced by your ambient temperatures surrounding your grow rooms. The longevity of LED lights is a huge thing to consider as well. Do your research!
The Advantages of Flowering Under Bluer LED and Eye Blue HID Lights
Here’s my story, and I’m stickin’ it to ya, heh heh. The first advantage of bluer color temperatures for your cannabis grow lights, especially when flowering, is the structural enhancement. Flowering plants past halfway into their flowering stage will often times tend to want to fall over, or branches will bend far downwards heavy with buds. You can pretty much say bye-bye to all that stuff when using bluer full spectrum intense lighting.
Whenever I say “full spectrum” I am referring to a spectrum close to that of the sun, as close as possible. In the photo above you can see the difference between the sun’s spectrum and the spectrum of a fluorescent bulb. The fluorescent bulb is for sure “cool” at 4,100 kelvins, but has a weak ass spectrum, and no intensity whatsoever.
Under bluer full spectrum lights, your plants’ resistances are higher, and speaking of higher, the resin production is higher using bluer full spectrum. The terpenes are more pungent as well. Yields between something like an HPS (3,000 kelvins) and an Eye Blue MH (6,500 kelvins), both full spectrum HID bulbs, will be just about identical. The difference will be the HPS buds will be a bit larger, while the Eye Blue MH buds will be denser and slightly smaller in size. But your Eye Blue MH buds will be noticeably more potent.
Some Other Differences When Flowering with Bluer Cannabis Grow Lights
Generally speaking, plants flowering under warmer color temperatures, around 3,000 kelvins, tend to use a lot of magnesium and calcium. Plants flowering under cooler color temperatures tend to use more nitrogen and potassium.
Cooler cannabis grow lights, also cause the plants to begin flowering a tad slower than warmer lights at the start of flowering. Don’t get your panties in a bunch, they make up for it with an extra fattening up spurt of growth right at the end of flowering—last 2 weeks or so.
Lastly, and perhaps most importantly, if you decide to try a blue halide for flowering, do yourself a favor and get the real deal Hortilux Eye Blue metal halide. They now work on digital or magnetic ballasts, and there just aren’t any blue HID bulbs out there that come anywhere close to the Eye Blue baybee. Don’t skimp here.
Afterword with Rev
I hope you are doing well out there my green amigos. I just made myself a big old honkin’ hashish ball that weighs 17 grams, heh heh. Good hunkering down supplies. If ya wanna, check out another cool article by yours truly here at SKUNK: Fading Your Cannabis with Rev
You can get the Agrosun MH bulbs for pretty cheap, but if I were you, I would spring for the 90 bucks and grab yourself an Eye Blue baybee! If LED shopping, well, I of course highly recommend the HLG 300 at 4,000 kelvins. However, there are really good LED lights out there you just gotta do your homework, and make sure they will last. Hope you try the blues … Rev out…
I'm The Rev, and I have been with SKUNK for about a decade now. I hail from Southern California, spent mucho time in Northern California, and now reside in Southern Oregon; always coastal. I am an all natural style cannabis grower and I have written a couple books on the subject - check out True Living Organics 2nd Edition on Amazon - I have been growing for over 45 years, and I have been breeding cannabis for over 30 years. Check out kingdomorganicseeds.com to see some exotic selections. Growing connoisseur cannabis is what I teach mostly, growing it in living soil without using liquid organic nutrients to feed the plant. I am also a highly skilled synthetics grower, hydroponics, aeroponics, DWC/SWC/NFT, Ebb and Flow, and soilless, but I cringe when smoking synthetic grown herbs, so for the last 15 years or so I preach the artisan style of all natural growing, specializing in container growing. Cheers and welcome aboard.