Most savvy marijuana growers have heard of the high-yielding high intensity discharge (HID) lighting technology known as double-ended bulbs.
You can view internet videos of bloom-phase grow rooms that utilize double-ended (DE) high-pressure sodium bulbs and environmental protocols in which yields exceed three pounds of dry weight buds per 1000-watt bulb.
These impressive returns come in part because quality DE bulbs deliver far more light intensity and photosynthetically active radiation (PAR) per watt than the standard single-ended bulbs cannabis growers have been using for decades.
Photosynthetically active radiation is the segment of the radiation spectrum that most stimulates photosynthesis. Old-school grow lights emit lots of light and heat, but aren’t engineered to transform most of the electricity they consume into wavelengths matching the ideal PAR spectrum.
The best double-ended grow lights are designed to efficiently convert watts to PAR, and to provide ultraviolet and infrared wavelengths that stimulate production of cannabinoids and terpenoids. In contrast, most brands of single-ended HID bulbs emit little if any ultraviolet and infrared wavelengths.
Here’s a very useful video that explains photosynthetically active radiation:
Not only are DE grow lights better for your plants’ growth rate, potency and yield, they also save you money because the bulbs deliver maximal, consistent light output for far longer than standard HID bulbs, and DE ballasts tend to last longer than standard HID ballasts.
Some grow-light testers report that even after 10,000 hours of use, quality double-ended bulbs can still output 83–93 percent of their original intensity.
Another benefit is that DE bulbs and reflectors deliver a larger light footprint than equivalent watt standard bulbs. A standard 1000-watt HID provides enough light for 16–20 square feet of garden space, whereas a quality 1000-watt DE grow light provides more PAR and a larger coverage area, between 20–30 square feet.
It’s easy to see that DE lights provide more and higher-productivity light to marijuana plants using less electricity and fewer lighting fixtures, and that growers using well-made DE grow lights don’t have to replace their bulbs and ballasts anywhere near as often as if they were using standard grow lights.
Double-Ended Grow Light Disadvantages
Until recent innovations in technology, there were technical and practical limitations that discouraged some growers from using DE grow lights. One big problem has been that increased light intensity and PAR generated by DE bulbs may be too strong for your plants, especially when bulbs and their fixtures are placed the same distances from the plant canopy as regular single-ended HID bulbs are placed.
I’ve seen marijuana leaves shrinking away from DE lights, even when the grow lights were 30 inches or more from the canopy. Problem is, the extra space you have to put between DE grow lights and your cannabis canopy is vertical space many growers just don’t have.
Growers in rooms with traditional ceiling height (about eight feet) or lower, and growers who use grow tents and chambers, have learned the hard way that full-size photoperiod cannabis plants can be burned by DE lights.
Because DE bulbs put out much more ultraviolet and infrared wavelengths than single-ended bulbs, plants too close to these stronger bulbs are overstressed, buds grow thin and airy, and crops are bombarded with too much light and infrared heat.
The default DE grow-light strategy has been for growers to use grow rooms with 10-foot ceilings, but this isn’t a viable option for most marijuana growers.
New Double-Ended Lighting Technology & Trends
The great news is that the DE grow lights industry has heard the grower complaints and as a consequence has created a new generation of bulbs, reflectors and ballasts that make these grow lights a great choice for a wider variety of grow-room situations.
Indeed, some manufacturers have created DE bulbs and accompanying ballasts that can run at 750 watts or less, not just at 1000 watts.
Some manufacturers reengineered their reflectors to create wider light distribution, decreasing the amount of overkill direct energy plants received from reflectors that were more narrowly focused.
DE grow light manufacturers now offer adjustable reflectors and reflector inserts that change the angle and profile of light thrown from a bulb, altering the hot spot underneath the lights to better accommodate situations in which vertical space is lacking.
It’s important to remember that double-ended ballasts, reflectors and bulbs are all part of one unit. This is quite different than single-ended grow lights that can be run as bare bulbs in a socket, or in various types of reflectors, with ballasts corded to the bulbs and/or reflectors, allowing placement of ballasts outside the grow room.
With DE technology, the bulb fixture, reflector and ballast are all in one conjoined unit, which somewhat limits grow-light placement flexibility, keeps ballast heat in the grow room, and has made it more difficult in some cases to use standard light stands or light movers.
It should also be noted that due to high temperature requirements necessary to keep a DE bulb stable and operating at maximal efficiency, most manufacturers don’t recommend using air-cooled reflectors with these bulbs. This means that when using DE lights, grow-room heat that can be removed from the space via a sealed reflector, ducting and exhaust fans when using regular HID lights will stay in the grow room. The heat must be removed via room exhaust fans and/or mitigated using air conditioning.
Bigger Yields & Less Electricity Usage
I recently spoke with a professional commercial grower who did a side-by-side grow op test to compare double-ended bulbs to regular HID bulbs.
He had two identically sized grow rooms boasting eight-foot ceilings, with sets of clones from the same mother plants. All growing protocols — hydroponics nutrients, temperature, humidity, added CO2, etc — were identical.
He started both sets of clones using T5 fluorescent bulbs for the first two weeks, then switched to identical metal halide single-ended bulbs in identical reflectors with identical ballasts to finish off grow phase.
The clones were all at the same height and stage of development when he started bloom phase. In one room he used three 750-watt iluminar double-ended grow lamps. In the other room he used three HID single-ended bulbs in reflectors, coupled with adjustable ballasts.
Even two weeks into bloom phase, he saw that clones growing under the DE lights were flowering earlier and showing more budding sites compared to the clones in the single-ended room.
Three weeks into bloom phase, he was shocked to see that the DE bud development was much thicker and more resinous than the buds grown under the single-ended light.
He admits to “compromising the comparability” of the experiment because he dialed up his standard ballasts to 1000 watts instead of the 750 watts he started at, hoping his plants in the standard HPS room would fill in and become as sticky as the buds in the DE room.
When he harvested, dried, cured and weighed, the numbers were starkly conclusive. From 2250 watts of DE lighting he produced two ounces shy of six pounds of dry-weight buds, which averaged to just under two pounds per 750-watt light.
From 3000 watts of standard single-ended HID grow lights he produced five pounds of dry-weight buds, which is slightly more than one-and-a-half pounds per 1000-watt light.
He used more electricity to run the single-ended HID room, not just because he ran 1000 watts per light instead of 750, but because the 1000-watt lights generated more heat than the 750-watt DE.
Plants grown under the DE lights had superior bud development, potency, resin gland percentages and terpenoid scent. Growers who cultivate marijuana to make concentrates report that DE grow lights produce more cannabinoids and terpenoids per watt.
The obvious return on investment increase from DE bulbs — coupled with the new generation of technology that allows growers to use the lights in rooms in standard-height ceilings — is spurring more growers to switch out their old-school lights for DE technology.
Guidelines For Getting The Best Results From DE Grow Lights
Optimize your hydroponics nutrients, CO2 levels and climate control so the increased PAR double-ended bulbs give you is integrated into an amped-up overall cultivation regime. This article contains a series of videos explaining how to run an optimized, high-input, high-yielding grow room.
Avoid using Gavita lighting. The company was recently taken over by Hawthorne, a subsidiary of Scotts Miracle-Gro. Scotts has long been in bed with environmentally harmful corporations like Monsanto, and has monopoly intentions in the hydroponics industry. Gavita DE lighting fixtures, ballasts and bulbs are much more expensive yet not more productive than lower-cost equipment from companies like Iluminar.
There are now metal halide and high-pressure sodium DE grow lights on the market. There are also many more manufacturers getting into the DE business. We advise you to visit your local hydroponics store and discuss with the staff your ceiling height in your grow space and what kind of growing system you use so you can see the gear and make the right choices.
The new generation of DE grow lights is very useful for screen of green and sea of green gardens grown in rooms with normal ceiling height or taller-than-average ceilings.
Initial startup cost for quality DE gear has decreased because new manufacturers have stepped in to provide items at a lower price point. You can now get a dimmable, 1000-watt DE HPS fixture for about $400. Always check with your hydroponics retailer to see if a DE fixture you’re interested in can run both metal halide and high-pressure sodium bulbs. Also inquire about warranties, and ask about complaints or compliments the store has received in regard to specific manufacturers or models you’re interested in.
The brand of DE bulb makes a big difference in performance and longevity. I recommend Ushio, Hortilux and Philips bulbs.
Invest in a PAR meter and use it to test grow lights before you buy them. Understand that a PAR meter is different than a lumens meter, which only measures the amount of radiation. A PAR meter measures photosynthetically active radiation. You can also use the meter to ensure ideal PAR penetration and coverage in your grow room.
Quality DE grow lights direct way more infrared radiation than regular grow lights. Your plants may be negatively affected by the radiation, especially if your grow room isn’t cooled properly so that the plant canopy overheats from absorbed infrared. If you see your plants’ leaves folding down away from the lights — almost as if they’re overwatered or are wilting yet overwatering and drought aren’t the problem — it could be that the infrared is overloading your plants. The fixes for this include better cooling and aeration of leaf surfaces, raising your DE lights a few inches at a time, and using inserts to spread the light footprint to relieve infrared stress.
In summary, we celebrate the fact that the days when double-ended grow lights could only be used by growers who had 10-foot ceilings are over. Get into the new generation of DE lighting so you too see bigger yields and lower costs in your grow room.