The Grow Light Selector Tool
What Type of Grow Light?

First, welcome to the grow light selector tool. If you are using your garden area to grow clones or seedlings, then you should use a fluorescent light (or two) to light your garden area. If you are using the garden area to grow plants in the vegetative stage to 14 inches tall (or less), then you will need to use 3 to 5 fluorescent lights or a small metal halide to properly light the space.

If you are using an area to grow plants in the vegetative stage larger than 14 inches tall, it is best to use a small to medium size metal halide light. High Pressure Sodium lights are also acceptable in this situation. Unfortunately, the light from a fluorescent grow light is not strong enough to support healthy plant growth beyond 14 inches from the fluorescent bulb, which makes them useful only for shorter plants.

Finally if you are growing plants in the flowering stage of plant growth, you should use a high pressure sodium light. These are just general guidelines, as I have also seen plants in the flowering stage do very well under a metal halide light. Ultimately the size of your light will depend on the size of the garden area you are trying to cover, and how large you intend to grow your plants before harvesting.

What Size Light?

Seedlings and clones, and even small plants in the vegetative stage, will do just fine under 20-30 watts/sq foot. Larger plants in the vegetative stage will do better if given a little more... about 30-40 watts/sq foot. Plants in the flowering stage require a lot more light, and should be given 40-60 watts of light per square foot. Again, these are general guidelines that should work well for most plants that require lots of light. It is always a good idea to know the lighting requirements of the particular plants you are growing.

The first step in choosing the size of light you will need is to measure the floor space of your garden area (example: 2 feet by 4 feet= 8 sq feet). Next, multiply this by the watts per square foot you would like (example: 8 sq feet times 50 watts/sq foot= 400 watts). Break out your calculator if you need to, this is important to your indoor gardening success!

In the example above, you would need 400 watts of light to illuminate a 2 x 4 foot garden at 50 watts/sq foot. As luck would have it, a 400 watt light is one of the standard sizes. The most commonly used grow light sizes are...

• 250 watts
• 400 watts
• 600 watts
• 1000 watts

You must choose the light that most closely fits your garden's needs. Keep in mind, a 250 watt garden will have a smaller yield. Also, I do not personally recommend using 1000 watt lights unless you are prepared to go the extra mile to keep temperatures down in your garden area. Check out this hot tip for the whole story.

Grow Light Selector -
About your Reflector

If the grow light selector tool has led you to a metal halide or high pressure sodium light, there are a few system options to consider. Lets look at a few of them...

The grow light selector tool really comes in handy for this part. A light reflector like this, that is not enclosed and not air-cooled by an exhaust fan, sends all of its heat out into the room, (where you must use a good exhaust fan to deal with it). If your garden area is open to freely exchange air with a larger room, this is the only time I would consider using this type of light.


Most of the time, however, your garden area will be fully boxed in, in order to be able to provide a dark period to force flowering. That is why I do not recommend these reflectors in general.

With the light fully enclosed and glass in the bottom, you can attach the light to an exhaust fan and control most of the heat at its source. Most of the heat will never enter your growing area. The less your airflow is obstructed, the better the cooling effect will be. Lets take a look at a few more things to consider.

A reflector with exhaust vents like this is better than a reflector with no exhaust vents. However...

when you turn the reflector over, you can see how the airflow will be slowed down by the tiny vents inside.

Even if this reflector had good, 4 inch vent holes all the way through, the airflow would still run into the bulb and be forced to flow around it (slowing the airflow).

This reflector, vented corner to corner, has the same problem.

In this two bulb system, you can see how the airflow would pass through the reflector in between the two bulbs (not blocking the airflow at all). This design is better, but there is still room for improvement.

The 6 inch vent holes in this reflector are not only large... they go all the way through, allowing a maximum airflow through the reflector.

Looking underneath, you can see how the air moves unblocked through the reflector, past both sides of the bulb (and not right into the bulb). This design provides the maximum, unobstructed airflow (therefore the maximum cooling benefit). This is the design that I use myself when growing in an enclosed area.

To check out some of the other stuff that I use, check out my most successful homemade hydroponic system.

About your Ballast

The grow light selector tool would not be complete without a section on your ballast. A ballast is a heavy electrical part that comes with every grow light. The ballast uses your home electric and "bumps up" the current to run high intensity discharge lights properly.

The biggest consideration with your ballast is the extra heat it generates. Most light systems, like the example above, attach the ballast to a long cord. This allows you to place the ballast in another area outside the garden area. This is called a remote ballast. Compared to having the ballast IN the garden area, the temperature difference can be as much as 10 degrees.

This is exactly the type of light you do NOT want to get. This light reflector is wide right here because it has a built in ballast, forcing you to deal with the extra heat inside your garden. I do not recommend using this type.

Several years ago, another option became available. This is the digital ballast. A digital ballast uses computer chips to draw and produce exactly the electricity needed to run your light in a way that maximizes its light output.

A standard ballast uses a coil to do this. The coil has a cycle to control electric output. At the top of each cycle, there is a little extra energy than is needed to run the light. This extra energy is wasted each time as the cycle starts over (which is constantly).

The end result is that a light run by a digital ballast will constantly put out slightly more light, and will do it using about 1/3 less electric. For my next system, I will have a 600 watt light with a well vented reflector and a remote digital ballast.

Getting the Best Lighting
From Your New Light

By now you have chosen a light with the grow light selector tool. The best lighting tips for your newly selected grow light can be found in one of the following areas...

• fluorescent lighting tips
• metal halide lighing tips
• high pressure sodium tips

Thank You for Using the
Grow Light Selector Tool

Leave the grow light selector tool and
Check out the Hydroponic System Design page


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Go to the General Garden Lighting Tips Page