A topic that has been covered a thousand times over, but we’ll do it as well. Some articles out there are pro LED, some are pro HID, others are neutral. While we’re pro LED, we’ll still try to highlight both pros and cons of these grow lamp types in a neutral and objective way. We do believe that HIDs are the better choice in some circumstances, but our general opinion is that LEDs are easier to manage/work with, last longer, and are more efficient. They are simply easier to get started with and there are both good options for beginners but also for pros. LED lamps do come with a higher up-front cost but typically this investment is returned in a year of growing due to savings in electricity as the average LED lamp is more efficient at converting electricity into light than a HID.
HID: HPS, MH, CMH
HIDs, or High Intensity Discharge fixtures is a category where HPS (High Pressure Sodium), MH (Metal Halide), and CMH (Ceramic Metal Halide) are all apart of. These are all bulb-type lamps but they are manufacturerd a bit different and have different characteristics. The bulbs are fixed to a ballast (“driver”) and there’s a reflector above the bulb so that the emitted light is reflected downwards. There are also double ended bulbs which are typically more efficient but also more expensive.
LEDs (Light Emitting Diode) also come in different formats. We have the usual LED light fixtures, thare are COBs (Circuit on Board), and QBs (Quantum Board, which is essentially just a LED panel with a driver). More on different LED types HERE. The common factor with LEDs is that the technology uses diodes instead of bulbs. A single LED grow light can consist of anything from a few diodes to thousands.
Management & longevity:
– HID: After the bulb has been fixed to the ballast and then the reflector mounted then the entire system is hung at an appropriate height, it’s good to go. The ballast and reflector will work for a long time but the bulbs degrade quickly and need to be replaced after about a year of use. Some replace them after each grow though. With most HIDs it’s recommended to use one bulb for veg and one bulb for flowering as they emit different colored light, more on this under Spectrum.
– LED: Unless you buy a DIY kit, LED lamps will come fully assembled and after you hang the system and plug in the cord, it’s ready to be used. The diodes typically last for more than 50.000 hours and well built fixtures only degrade about 30% during the first 50.000 hours. 50.000 hours works out to 2777 days or 7.6 years if the lamp is operational for 18 hours a day (which is a high number), every day. No need to change diodes either. The standard setup works both throughout veg and flowering stage.
Spectrum refers to what type of light color a lamp emits. In recent years interior design trend is to use colored LED bulbs or strips to add a bit of zazz to one’s home. Some are red, some are blue, some are green, etc. White light consists of all colors; blue, green, yellow, red. A combination of these makes white light. If there’s a hint more blue, then the light will become so called “cold white”. More red would make it “warm white”.
The sunlight’s spectrum looks like this:
Plants have been thriving under this spectrum from millions of years and they still do. So we’ll want to replicate this spectrum to some extent. Arguments have been made that plants do not need green light as photosynthesis is mostly triggered by blue and red light. While this is true, research and studies have confirmed that some green light helps with plant health and appearance, so it should not be ignored.
Here’s an illustration of what wavelengths (light colors) that drive photosynthesis in plants:
Now let’s take a look at what spectrum HIDs and LEDs typically emit.
A quick search for “HPS spectrum” on Google gives us this image:
We see right away that the peaks, i.e. the most intensive light colors, are nowhere near the photosynthesis trigger curve.
– CMH spectrum:
Here we see that the spectrum has a broader reach and covers more of the colors that benefit photosynthesis. Still, we see a lot of emitted colors that are not too efficient. Remember: electricity is required to produce light so the part of the spectrum that is of little use for plants is “wasted”. I.e. you are paying for the electricity but the result (the emitted light) does not do a whole lot for your plants.
– LED: As each diode can be customized to emit any color visible to the human eye, it’s easy to make efficient and spectrums. Manufacturers can select diodes that together produce the desired spectrum. It can be all blue, or all green, or all red. Any kind of spectrum is possible.
With our knowledge about photosynthesis and plant health we’ll want a spectrum that has a decent amount of blue light, a decent amount of green but plenty of red as it is the red light that primarily benefits plants during their flowering stage, when they produce buds.
There are bad LED lamp spectrums out there though so don’t believe all LED lamps are good.
Some manufacturers opt to use only blue and red diodes which makes for this spectrum:
We see that there is some blue but almost no green, then massive red spikes. While this may be efficient, it doesn’t fully stimulate plants.
Here’s another, better, example:
Here we see a fairly good balance of blue-green-red. Possibly a bit too much cyan, green, and yellow but definitely better than the previous example.
Some researches say that a balanced spectrum of approx 20% blue, 20% green, and 60% red is the ideal combination for a full cycle grow.
Efficacy (umol/J or PPF/W):
Efficacy is a term used to describe how well, or how efficiently, a lamp converts electricity into light. Sort of like miles per gallon or kilometers per liter when talking about cars, but reversed. The higher the efficacy, the more efficient the lamp is at producing light, whereas with cars you want as low number as possible. Efficacy is measured in umol/J, micromoles per Joule. The efficacy rating is based on the total light output from the light source. What’s not account for is where this light ends up. A significant amount of light can be lost through reflection or missing its intended area (the canopy of your plants).
– HID: The best HIDs, double-ended Gavita Pro 1000W (~$600), can reach up to 1.8 umol/J efficacy. The more wattage, the higher efficacy, to some extent. The more budget and beginner friendly HIDs are clocking in at around 1.0-1.4 umol/J.
– LED: Today, in mid 2019, the top of the line diodes that are used commercially clock in at around 2.4 umol/J (white diodes) to 3.0 umol/J (red diodes). Once they have been fitted to the lamp and some driver loss is accounted for, the best performing LED lamps (quantum boards) typically operate at around 2.1 umol/J (~$1000 for a Quantum Board that has Gavita-comparable reach).
Price matters, quality costs. Diodes and lamps with high efficacy are more expensive than diodes with low efficacy. Low end LED lamps at around $70-100 (regular fixtures, not COBs or QBs) usually run at 0.7-1.0 umol/J. We see this with Mars Hydro, Viparspectra, Bestva, etc.
A bit more higher end LED fixtures that sell for around $150-200 may reach 1.5 umol/J, or around that neighbourhood.
How about an example to put things into perspective?
We have two lamps, A and B. Both lamps produce the exact same spectrum but lamp A operates at 0.8 umol/J efficacy while lamp B operates at 1.6 umol/J (twice the efficacy of lamp A). This means that lamp A needs to draw twice the power to produce the same amount of light as lamp B. Or, a different approach, lamp A produces half the light output as lamp B if they draw the same amount of electricity.
Wattage (power consumption):
Power consumption or draw power refers to how many watts, or how much electricity a lamp consumes per hour. This data will be shown by the manufacturer. It’s good to know the draw power as that lets you calculate how much the lamp will cost to run hourly, daily, monthly, or yearly.
Very, VERY, oversimplified: the more wattage a lamp draws the more light it emits. While this can be used as an indicator, it’s not very accurate on its own. As we saw above, efficacy and spectrum also play into the mix. Don’t look exclusively at draw power (watts) but do use it as an indicator to get an idea of a lamp’s output. For instance, a 50W lamp will never be able to put out the same amount of light as a 300W lamp. Well, if the 50W lamp would have six times the efficacy of the 300W lamp then they would be equal but such large differences in efficacy don’t really occur.
Some manufacturers also tend to market their lights based on their total diode wattage, eg. 50 diodes at 10W each would make a “500W” lamp. This incredibly misleading and does not say anything at all about the lamp as a whole or its performance. More on this HERE.
Point being: look for draw power and not total diode wattage.
HDI vs LED wattage:
People typically say “my LED lamp draws much less power than my old HID/HPS!”. While this can be true, and in most cases it is true, it’s important to also consider efficacy and spectrum to understand the most crucial point: light output. If a lamp has low draw power but also low light output, then you’re most likely doing yourself a disfavor as the lower light output will likely affect your yield. Lower power consumption is overall good and should be aimed for but only if the lamp still produces enough light output (PPF), and the light is projected onto the designated grow area (PPFD, more on this further down).
Heat is directly tied to wattage. There’s a term called British Thermal Unit, Btu, and this tells us that 1 watt produces 3.41 Btu/h. Btu is a type of measurement for temperature but not exactly like Farenheit or Celsius. The definition of Btu:
“One Btu is equal to the amount of heat required to raise the temperature of one pound of liquid water by 1 degree Fahrenheit”.
In short: no matter if you’re using LEDs or HIDs, the heat produced by either one of these lamp types will be the same as long as the draw power (watts) is the same.
One 300W LED lamp will produce the same amount of heat as a 300W HID.
The reason LEDs are generally considered more cool running than HIDs is that an average 200W LED can usually replace aan average 300W HPS. Or an average 400W LED can replace an average 600W HPS.
The reason I keep saying “average” is because, as we discussed above, this has a lot to do with spectrum (light quality) and efficacy. A very poor LED lamp with low efficacy (let’s say 0.7 umol/J) would probably be equal to an HID, i.e. a poor 200W LED lamp would give about the same light output as an average 200W HID. However, a good LED lamp (decent efficacy, 1.4 umol/J), would be much more efficient than an average HID. Here it would probably be enough to have 200W LED to replace a 400W HID. This is, of course, a bit generalized and simplified but I hope you get the idea.
Light footprint (coverage):
Okay, this is pretty important and most of the time HIDs beat LEDs in this regard. When growing weed indoors under any light source, you want that lamp to give an even light distribution across the canopy of your plants. Light intensity is measured in PPFD and mature plants will want about 600-800 PPFD. If you’re unfamiliar with PPFD, we have a separate article about it HERE.
– HID: As HIDs have one single bulb that emits light in ALL directions, 360 degrees, but with a reflector on top so that the light is reflected downwards, the intensity of its footprint will be much more even compared to LEDs. Let’s take a look:
From Sanlight.com’s site where they test the footprint of a 250W(!) HPS at 20 inches (50 cm) height in a 80×80 cm tent, which is almost 3×3’. We see that the center value is 560 PPFD (umol/m2/s) and even (almost) at the outer edges it produces 350 PPFD or above. The difference between the outer edges and center spot is only 210 PPFD or 60% (560/350). Let’s take a look at a LED light.
Most LED lamps, especially in the beginner friendly segment, have a perfectly even distribution of their diodes on the board of the lamp. While this may sound good, in practice this creates very intense hot spots right below the lamp. The spread of the light is worse than with HIDs so the light won’t reach as far off-center and the outer edges will have very low light intensity, in general.
Footprint Viparspectra V450 (200W draw):
Footprint from Vipars website. Here we see a 36×36” footprint map, which is 3×3’ (or 91×91 cm), nearly the same as the HID example. The lamp is hung at 18” (45 cm) from the ground. Here we see intense values in the center spot of 622 PPFD (umol/m2/s) but we’re already seeing a massive drop by nearly half as we move to the outer edges of the 1×1’ corner.
At a 18” distance off center we see values between 94-78 PPFD. Compare this with the HID’s 350. The HID produces 3-4 times as intense light as the LED 18” off center.
Also note that the difference between the 18” off center value and the center value for this particular LED lamp is a whooping 691%! (622/90). This means that the center value is almost 7 times higher than the 18” off center value. What we learn from this is that this LED lamp would only produce enough light in the 1×1’, possibly 1.5×1.5’ area underneath the lamp. It would definitely not cover a 3×3’ tent with enough light for cannabis plants.
Some LEDs are better in this regard, some are worse. What we learn here is that it’s important to consider the light footprint and make sure that the lamp produces and even distribution. If you’re only growing one single plant then 1×1’ would be enough for you meaning that it would be a waste to have the HID. Two plants would be borderline. If growing three or more plants, the HID would come out on top. Know your grow space and based on how many plants (how large area) you grow, select a grow light that gives a decent light footprint.
The larger a LED lamp’s surface is, the larger is it’s light footprint. Most LEDs in the budget/beginner category are, however, about 1×1’ or 30×30 cm. A large LED lamp would spread its light in a wider area thus creating a larger light footprint.
Both HIDs and LEDs have their pros and cons. HIDs give a better light coverage and cost a little bit less upfront but they also require bulb changes, bulb replacements and often produce more heat and draw more power than their comparable LED counterpart.
LED technology is evolving very quickly and in the last 1-2 years alone we’ve seen great improvements in efficacy and general performance. The fact that LED lamps’ light spectrum can be customized to give a more targeted output is a big upside. As LEDs typically require less power and produce less heat, which is good if you’re growing in an already warm location or enclosed space. A LED lamp will last for 5+ years (often 10+ years) without any major deterioration.
A growing problem with LEDs is that on online marketplaces, like Amazon and Ebay, more and more Chinese brands than build well,… questionable… quality lights are emerging. They are all racing to produce the cheapest possible light and both the build quality, fire safety, and performance suffers. It’s difficult for consumers to tell one lamp apart from the other, especially with the sly and misleading marketing tactics (like total diode wattage = lamp wattage, as mentioned above) and almost identical builds. Our recommendation: choose a brand that’s not Chinese. It should be quite easy to tell US/EU brands apart from Chinese just by reading the product description. Chinese are getting better and better at English but they still make enough spelling and grammar mistakes for you to see through their listing.