Grow lighting: HPS or CFL?

Question

I am not sure what kind of grow lighting I should get. I plan on growing 2 plants but I am on a tight budget and have a very small grow space (only 32" high). I've heard you can grow plants in very small spaces like a computer case, so this cupboard should be big enough.

I thought a 150w HPS grow light would be a bit big/hot for my space, so I'm thinking about going with CFLs instead. What do you recommend?

Summary:

• Plan on growing 2 plants
• Short grow space (32" / 80 cm)
• 150W HPS or CFLs?

Answer

It depends.

CFLs are generally better suited to such a small growing space. They will do the job of getting plants to grow and can produce dank buds, but will take more work from you on a regular basis as you'll need to adjust the lights every few days. These lights must be kept very close to your plants, and plants quickly grow into the lights if you're not tending your garden.

HPS grow lights don't need to be adjusted as often and they produce a more intense light (greater lumen/watt ratio) that gets plants to grow faster than with CFLs. Generally you'll get better overall results with an HPS (though CFLs can definitely produce dank buds too). Yet in such a tight grow space, an HPS takes up several more precious inches of vertical space than CFLs.

Heat

No matter which one you choose, you're going to need ventilation to control the heat in such a small grow space. CFLs run cool, but they'll still heat up a small space quickly.

I've used both CFLs and a 150 HPS in a cupboard, and the most important factor is using an exhaust system with a fan to constantly move the air and keep temps down.

Home depot and/or most home improvement stores sell 70 CFM bathroom fans, which exchanges air faster than a 150W HPS light can heat up your space (these fans cost around $35). You would place the fan in your exhaust hole at the top of your grow space, and use the fan to pull all the hot air out through the exhaust.

Space

As you stated, an HPS will require more space than CFLs. In addition to the size of the actual HPS bulb and reflector, you must consider that a 150W light will need to be kept further away from the tops of plants (usually 6-8").

In a cool environment, I've seen growers keep the tops of plants just 3" away from the glass of a 150W reflector, but that's as close as you could possibly get, and would require that you use a good fan to vent out all the heat through an exhaust hole that goes outside.

This HPS light is 7" tall. So if you consider that plants must be 3" (or more) away from the reflector, that means the light takes 10"+ of space, leaving you with less than 22" for your plants and their containers. It's quite a tight fit, but it can be done, especially with training techniques to keep your plants short.

With CFLs, bulbs placed horizontally take up just a few inches, and plants can be kept just 2" away. That means CFLs only need about 5" of vertical space, giving you quite a few more inches for your plants to grow. There really aren't any other grow lights that need less space than CFLs. This is why CFLs are so popular for cupboard and PC grows.

It's really a toss-up as far as space. Would you rather spend your time training plants to grow short, or would you rather tend to your CFL lights? In a small space like yours, it's hard to say for certain what's actually going to be easier for you.

Speaking of space, you may also want to consider looking into auto-flowering strains, as they naturally grow very short.

Electricity

A 150W HPS light draws about 160W of electricity to run. That's less than your average TV or desktop computer, and comes out to less than $5/month where I live even if you're running the grow light all the time.

CFLs don't produce as much light per watt as an HPS, so they are less efficient (as far as how much light is produced compared to how much electricity they use).

Just to give you an example, if you buy 6 x 26W CFLs, you'll be using about as much electricity as a 150W HPS and you'll be producing less light, but you'll also have more room in your grow space for your plants, and you'll have more freedom to arrange the lights as you want around the plant.

Safety

Safety is another thing to consider that a lot of people forget when choosing grow lights. Doing everything DIY (like with CFLs) is cheaper, but adds safety risks since they're not designed for gardening.

When you buy products that are specifically designed for growing, there are more safety features. If you use 5+ CFL bulbs in a small space you increase your risk of fire or other accidents. More sockets... more plugs... more heat.... All things to consider.

Results/Yields

Both HPS and CFLs can produce stellar results. My first few grows were all with CFLs, and I was impressed with the quality and potency of my buds. Yet nothing beats the density and bag appeal of buds grown under an HPS.

As far as yields, it really depends a whole lot on your grow style and how well you adapt to using each type of light. The skills it takes to master an HPS are different than the skills needed to master CFLs. It's been proven that both options can produce a few ounces of buds in a small space, but it's almost impossible to definitively say that one option is better than the other.

Jump to...

Learn more about growing with CFLs

How do I grow weed in coco coir with CFLs?

Learn more about HPS grow lights

How do I choose the right HPS grow light?

What's the difference between regular and autoflowering strains?