Difference Between HID And MH Bulbs

HID, HPS And MH Bulbs Explained

If you’re just beginning your first hydroponic garden, you might be overwhelmed by some of the lingo. While hydroponic gardening is easy to do once you’ve got the hang of it, many beginners find themselves hung up on the confusing language alone. 

One of these issues is in knowing the difference between HID and MH bulbs. While these acronyms may not mean a lot to you now, learning how to tell the difference between the two - as well as why it matters - is crucial as you begin your hydroponic garden.


What Do HID, MH, and HPS Stand For?

HID stands for High Intensity Discharge lighting. Essentially, this is just a light bulb, yet a very large light bulb. It lives in a sealed tube filled with gas, which creates light when the gas is ignited. 

A household bulb works in a similar way, utilizing a tiny metal filament to light the gas. In a HID bulb, on the other hand, two electrodes arc current to light the gas. HID bulbs are also frequently called HPS bulbs, so if you see them used interchangeably, don’t be confused. 

These bulbs are large - about the size of your arm, in some cases. These bulbs differ further depending on the type of gas they use to power themselves. An MH bulb  is powered by metal halide, hence the name, while an HPS bulb is powered by high pressure sodium.

Metal Halide (MH) Bulb - Used For Vegetative Cycles

High Press Sodium (HPS) Bulb - Used For Flowering Cycles

What is the Difference Between an MH Bulb and an HID Bulb?


Both types of bulbs are associated with hydroponic lighting, and both contain several key components. Each bulb will be powered by a ballast, and also include two additional items: a hood to help reflect light and maximize the bulb’s reach and potential lighting ability, and the bulb itself. 

The main difference between the MH bulb and the HPS bulb is the colour of the light they produce. Different gases produces different colors of light, so you can change up the kind of bulb you are using depending on the stage of growth your plants are in, as well as their particular needs at that time. 

HPS bulbs tend to have warm colors - think red, orange, or deep yellow, while MH bulbs are cooler - like blue or purple. HPS bulbs are needed when your plants are flowering and setting fruit, while MH bulbs are better at producing lush foliage and vegetation. 

MH Light Example

HPS Light Example

Above is an example of a grow side by side in the vegetative period. You'll notice MH provides much better results in the growth phase. 

How Does a HPS Bulb Work?

HPS bulbs contain a ton of pressure, as well as liquidized sodium. When electricity enters the bulb, an arc is created that travels from the ceramic arc tube in the bulb. Sodium vaporizes when it meets the heat from the bulb, and as temperatures increase, the bulb gives off the warm yellow light. 

These tubes get extremely hot, and are often found  in highway lights in addition to in hydroponic growing systems. They are a great choice for your hydroponic garden, but don’t expect to work beneath them for long - their hot orange glow can make it hard to see.

How Does a MH Bulb Work?

These bulbs tend to have a crisper, paler color than HID bulbs. The arc tube in this kind of bulb is made out of quartz glass, mercury, and various combinations of metallic halides. These halides are responsible for producing the crisp blue light that help your plants thrive so well. 

The tubes operate at high temperatures, and, in addition to hydroponic indoor gardens, are often found in places like warehouses or parking lots. They can deal easily with temperature fluctuations because they are coated with reflective powder. This helps reduce stress and makes them last for a long time even under challenging conditions.

Which Kind of Bulb Should I Choose?

Again, consider your plants’ needs when selecting a bulb for your hydroponic garden. You can easily swap these out between stages, making it easy to adapt your lighting to your plants’ changing needs. 

Keep in mind that HID bulbs always require some sort of a reflector to make them more efficient, and that they can produce considerable heat. Make accommodations so that the heat can be contained and does not cause problems with your plants or the safety of your system. 

You also need to remember that HID and MH bulbs cannot be interchanged without first changing their ballast. Each kind of bulb operates in a unique way, and needs a different ballast so that your plants receive the optimal lighting conditions. Both bulbs also need to be installed with the correct base lamp, but both can be found with medium and mogul base screw in connections. 

High pressure sodium bulbs promote flowering and fruiting, as already mentioned, and generally produce more lumens of light per watt. Metal halide bulbs produce fewer lumens of light per watt, but with a white, cool light. Both bulbs last around the same amount of time, but in general, a high pressure sodium bulb will last slightly longer. 

Metal halide bulbs should be used during the early stages of planting and plant growth, because it will help the plant grow when there are shorters paces between the branches. Later, you should switch to a high pressure sodium bulb. That being said, you can streamline this entire process by choosing a conversion bulb.

HPS Bulbs Are Use For Flowering Cycles And ONLY Run On HPS Ballasts. 

Use MH + MH Conversion Bulbs For Growth And Vegetative Cycles. (MH Conversion Bulbs Are Able To Run On HPS Ballasts Saving The Cost Of Buying An Additional Ballast). 

What’s a Conversion / MH Tubular Bulb?

As if you weren’t befuddled enough, there enters another option for lighting your hydroponic garden - the conversion bulb. This type of bulb allows you to run a MH bulb on a HPS ballast. They can help save you money by eliminating the need to switch between two fixtures, and also give you extra space in your grow area, since you won’t need two separate ballasts. 

Ultimately, you should be using all types of bulbs within your hydroponic growing system. You will have the best result if you run both bulbs at all times, but this is likely not practical both in regard to space and to expense. Instead, consider using a conversion bulb to eliminate the need to switch back and forth. Alternatively, you can use MH bulbs during seeding and vegetation development, and HPS bulbs during flowering and fruiting to get the most bang for your buck.


Here is an example of a MH bulb that will run on HPS equipment - making the need to buying a seperate MH ballast a thing of the past!

MH bulb that works on HPS equipment

Other Types Of Growing Lights Available


HPS + MH Grow Lights - One of the most common lighting used in hydroponics. Along with the bulbs - ballasts and hoods / reflectors  are also needed. 


Fluorescent Grow Lights - Commonly used for seed raising, small cuttings and clones and also work well for specific plants. 

CFL Grow Lights

CFL Grow Lights - These are probably the most affordable way to grow. The CFL bulbs come with a range of different spectrums and fit into regular household sockets.  

LED Grow Lights

LED Grow Lights - LED's are becoming more and more popular and as the technology advances it's getting hard to beat them on results and features. Currently you can get a high quality LED for about the same price as a HPS + MH set up. 


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