LED’s or MH/HPS grow lights

What to use for your Cannabis plants

400W LED light system and MH/HPS light bulbs

Hey there and welcome (back) !
In today’s article we’re going to look over the 2 main lighting systems that are available for an indoor growing system; LED’s and the MH/HPS combo. If you need to review what these bulb types are we’ve done a little piece available over here, don’t hesitate to check it out 😉

Since the MH/HPS combo is used together we will group them into one category, although they do have some differences, which we will point out when needed, let’s get into it !

LED or MH/HPS Lighting system – Table of content

Grow light systems – Overview

There are basically 2 categories of light systems that are available in order to get your Cannabis plants, the MH/HPS combo and LED systems.
Before going further it’s important to define each so everything is clear

Metal Halide and High Pressure Sodium Lighting System

Metal Halide and High Pressure Sodium and 2 types of light bulbs that provide the full light spectrum needed for a healthy plant.
While the MH bulb provides a large spectrum, the HPS bulb provides much warmer colors, let’s look at each in detail

Metal Halide (MH)

As you can see on the graph on the right hand side, the MH light bulb provides a full light spectrum with a peak in yellow wavelengths.
Although it can be used through the lifecycle of Cannabis generally it is only used during the vegetative stage since that is when the plant mainly needs the blue light spectrum for growth.

Wavelengths of Metal Halide light system

Graph credit to Wikipedia

High Pressure Sodium (HPS)

HPS light bulbs focuses on a much “warmer” light spectrum than it’s MH counter-part.
There’s very little short (violet/blue) wavelengths, with a concentration from the hot greens to the cooler reds.
These wavelengths are well adapted for your babies once they’ve entered the flowering stage as they replicate well a hot summer sun.

Growers generally operate the change between the MH bulb and the HPS bulb during the stretch, once the plant has stopped vegetative growth and developed multiple bud sites.

Wavelengths of High Pressure Sodium light system

Graph credit to Wikipedia

Light-Emitting Diode (LED) Lighting System

LED systems may vary depending the type of diodes on your system. Generally these systems provide a large light spectrum, similar to the MH bulb, as you can see on the image aside.

As much as we could tell LED systems do seem to render less flowers in comparison to a MH/HPS combo. Is it linked to the light spectrum though, hard for us to say for sure..

spectrum of light emitted by LED lights

Graph credit to Comsol

LED and MH/HPS lighting system – Pro’s and Con’s of each

Obviously both system do have their advantages, or else this piece would be moot. In this section we’re going to look over the strength and weakness’s of each. We’re basing this off our personal experience with each as well as what is said on the web.

Advantages and Disadvantages of LED and MH/HPS grow lights

Pro’s and Con’sLED systemMH/HPS system
Light Spectrum emittedLarge light spectrum, ranging from blue to red.
May differ depending on the LED system purchased.
MH : Large light spectrum
HPS : Focus on warm spectrum, well adapted for the flowering stage.
Heat producedLow heat emission
The diodes hardly emit any heat, definitely a strong point for LED’s on those hot summer days
MH and HPS lights emit a large amount of heat.
Depending on the wattage and the size of your tent, it can be hard to keep the grow room under 30°C 
Electric ConsumptionLED lights are known for the savings on the electric billAgain on this end MH/HPS bulbs don’t get the upper hand here as they consume more than LEDs
Flower YieldHere a LED grow system does seem to render less at the final harvest.
To be fully transparent we’ve only done 2 flowering runs with the LED lights.
There a reason why the MH/HPS stays the main indoor grow setup, the light spectrum is well adapted. 
If you manage the other aspects of the lifecycle you will get the most out of your plants. 
Danger for the eyesHonestly these suckers hurt, you’ll need to get protective glasses if you don’t want to destroy your eyesight, especially if you go over 150W ^^Due to the Blue Light, Metal Halide bulbs will may you a headache/migrane if you’re in contact for too long.
Repeated exposure without protective glasses will most likely do damage.
HPS bulbs are much smoother on the eyes, the warmer spectrum is much less agressive, although still bright.
Life of the systemDiodes count in the 10.000+ hours of life although you have to be careful on purchase.
We’ve seen a large number of complaints linked to diodes dying out very quickly after purchase.
That said, when you do have to replace them there’s the cost is much more significant.

MH/HPS systems generally last between 2000 and 5000 hours.
To give you a measure, we’ve used our MH/HPS for the past 5 grows and they’re still working fine.

The cost of replacement is pretty cheap, generally a bulb will cost you around 20 bucks.

MH/HPS and LED grow lights – Recap

We’re pretty conflicted here and it’s hard to make a clear cut between both.
On one hand, MH/HPS bulbs provided a well adapted light spectrum which allow maximum yield, but they consume more electricity and produce more heat… which, you know if you’ve had the issue, can give some bad headaches.

On the other hand the LED system produce little heat, consumes less electricity, but have a broader light spectrum that can hardly be adapted for the flowering stage, reducing final yield.
You’ll also need to get protective glasses in order to protect your eyes because they will do damage to your eye sight, especially with repeated exposure.

On our end, for the past couple months we’ve been running full LED and feel “ok” about it. Our plants mothers in the vegetative tent seem fine, although we’ve observed some little pistils, which got us a bit worried. On the flowering side it’s definitely a plus during the summer time and heat is really an issue, during winter not convinced at all and our last run didn’t give points to the LED system.

The right choice might be down the middle, with LEDs running during the vegetative stages and a HPS setup during the flowering stage… which we will test out soon, keep you posted ! 

Until then, 
Be safe and grow easy

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