Metal Halide Vs HPS Grow Light Bulbs

It can be really confusing.

HID, HPS, MH, wtf?

So many acronyms and even if you know what they all mean, you then need to figure out which one you want.

So I’m going to make your life a little easier by explaining the difference between HID, MH and HPS and helping you decide which one you want.

If you’re just looking for a quick answer: you want all 3.

But that’s because one includes the other two. Let me explain.

And if you just want to know which bulb is best for your needs, head here.

 

Metal Halide Vs HPS

Before we get into the comparison and determine which type of light is best for growing plants, let’s briefly take a look at each of the 3 terms, (HID, HPS and MH) individually, so that we know exactly what each means. We can’t compare them if we don’t understand them, after all.

 

What Does HID Mean?

HID stands for high-intensity discharge.

HID lamps are electrical gas-discharge lamps. This means that they produce light by creating an arc of electricity between two electrodes that are housed inside a tube filled with a noble gas.

They provide much more light per watt (i.e. are much more efficient) than traditional incandescent and fluorescent bulbs.

There are several different types of HID bulbs, with the main difference being the gas they contain. HPS and MH bulbs are two of those types. We’ll briefly discuss another, better and more modern, type below.

All HID bulbs require a ballast to start and maintain the electrical arc, in addition to a reflector to house the bulb.

For this reason, we always recommend buying a complete lighting kit instead of individual components, if you are just starting out.

Not only does the kit include everything you need, so you don’t end up missing a vital component, but kits also save you quite a bit of money over buying everything individually.

 

What Does HPS Mean?

HPS stands for high-pressure sodium, which refers to the type of gas contained inside this lamp. HPS bulbs give off a light with a reddish/yellowish color spectrum.

Bulbs containing sodium are often used in street lights, which is why those generally have a yellowish glow.

When it comes to growing plants, HPS bulbs are the preferred type, especially during the later stages of growth.

In those stages, plants will begin producing buds, flowers and fruits. They want a lot of red-spectrum light at this point in their light cycle, making HPS bulbs great, but not ideal. Other types of bulbs are better for flowering.

 

What Does MH Mean?

MH stands for metal halide and just like HPS, it refers to the gas inside the bulb. Metal halide lamps give off a whiter/bluer light than HPS lamps.

This light looks more natural to our eyes (i.e. it is closer in spectrum to sunlight during the middle of the day).

Plants want a lot of blue spectrum light during the early parts of their life cycle, when they are seeding and vegging. The light from an MH bulb promotes growth better than the reddish HPS light, making metal halide lamps ideal for the early stages of plant growth.

 

Metal Halide Vs HPS: So Which Bulb Should I Get?

The best answer is both.

You’ll get the best results if you run both bulbs all the time, but this is quite expensive, so we recommend using MH bulbs during seeding and/or vegging and using HPS bulbs during flowering.

If you only use one bulb throughout the grow cycle, you’re better off going with HPS. It will result in spindly plants (due to lack of blue light, which helps plants grow strong), but using MH during blooming is worse.

MH bulbs are one of the best lights for vegging cannabis, but using them during flowering has a fairly large negative impact on yields, because flowering plants really need that red light.

Read this article for more on the effect of different colors of light on plant growth and development.

While both high-pressure sodium and metal-halide bulbs have worked well to grow marijuana for many decades, the truth is that their spectrum is not ideal. Combining the two makes it much better, but it is still relatively inefficient compared to some of the more modern options.

When it comes to HID lighting, ceramic metal halide (usually shortened as CMH) is much better suited to plant growth. CMH bulbs can have varied spectra, but they are all much more complete than HPS or MH. They give you a great wavelength distribution that is most similar to natural sunlight out of all HID options.

CMH bulbs are also more efficient than HPS or MH, they emit less heat, and the last longer. We have an article on the best CMH bulbs and systems that has a lot more information on these lights.

And then, of course, there are LED grow lights. Since this article is about HID lighting, we won’t go into LED too much, but we should mention it, because the technology has improved so much that these lights are now far better than any HID light, even CMH.

In the past, the cost of LEDs was always too high, but that is no longer the case. There are some great budget LEDs on the market, like the Spider Farmer lights.

They do still cost more than HID, but not much more. You’ll easily make back the difference within a year in cost savings, because they use far less electricity and emit far less heat, so you won’t have to spend nearly as much on cooling.

They also last a lot longer, are safer, easier to operate (no bulb changes) and are better for the environment. This article has much more on LEDs vs HPS. We also have one comparing LED grow lights vs metal halide.

 

HPS Vs Metal Halide: Final Thoughts

In the end, the best answer to the HPS vs. MH debate is to go with CMH or LED instead. That’s probably not the answer you were looking for, in which case, follow the advice above.

A mixture of HPS and metal halide bulbs is best and using MH for the vegetative stage and HPS grow lights for flowering is second best. If you only use one for the entire grow, make it high pressure sodium.

MH only won’t work well for flowering. As a bonus, HPS bulbs tend to last longer, too. Always check every bulb after buying it to see if it is any good. Learn how to tell if a high pressure sodium bulb is bad.

 

Image Attribution

• Image 1: By Ozguy89 at the en.wikipedia, CC BY-SA 3.0, Link
• Image 2: By Sakurambo at en.wikipedia [GFDL or CC-BY-SA-3.0], via Wikimedia Commons
• Image 3: LMRoberts at en.wikipedia [CC BY-SA 3.0 or GFDL], via Wikimedia Commons
• Image 4: LMRoberts at en.wikipedia [CC BY-SA 3.0 or GFDL], via Wikimedia Commons