HPS vs MH 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.
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.
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 ideal.
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 bulbs. 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.
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. It has a fairly large negative impact on yields, because flowering plants really need that red light.
- Image 1: By Ozguy89 at the English language Wikipedia, CC BY-SA 3.0, Link
- Image 2: By Sakurambo at en.wikipedia [GFDL, CC-BY-SA-3.0 or CC BY-SA 2.5-2.0-1.0], via Wikimedia Commons
- Image 3: LMRoberts at English Wikipedia [CC BY-SA 3.0 or GFDL], via Wikimedia Commons
- Image 4: LMRoberts at English Wikipedia [CC BY-SA 3.0 or GFDL], via Wikimedia Commons