How much area are you looking to light?
The best place to start is to figure out the square footage of the area you are trying to light. For high-light plants like tomatoes you will want to achieve around 40 watts per square foot for optimal growth and fruit production. For low light plants, and small leafy plants like herbs and lettuce, you will only need to achieve about 25 to 30 watts per square foot. When figuring your area don't necessarily go by the actual size of the room. You will want to measure only the plant area that you will be growing in. In other words, if the grow room is 5 x 5, but you will only be growing in a 3 x 3 area there is no reason to get a light big enough for the whole room. Using that as an example, you have a 3 x 3 growing area so you must figure out how many watts you will require to light that area. We will be growing tomatoes so we will want to achieve 40 watts per square foot.
Width x Depth = Square Feet, e.g. 3 x 3 = 9 sq. ft.
Watts x Square Feet = Desired Wattage, e.g. 40 x 9 = 360 watts
We will just round the 360 watts up to 400 watts. So, we know that we will be in the market for a 400 watt grow light...
Should I Purchase a High Pressure Sodium or Metal Halide Grow Light?
Traditionally gardeners would use the Metal Halide fixtures for vegetative growth and the High Pressure Sodium (HPS) fixtures for flowering. According to some gardeners, flower volume and fruit weight can increase by as much as 20 percent when using HPS lights for flowering. But, Metal Halide is a very balanced spectrum and works very well for leafy vegetables like lettuce and herbs. Many growers will use the Metal Halide spectrum for vegetative growth and switch to HPS for the flowering cycle. In recent years switchable ballasts have been introduced in 400 watt and 1000 watt configurations, which allow you to run a HPS or Metal Halide bulb off of the same ballast. Since we will be growing tomatoes which spend most of their time flowering, we will go with the High Pressure Sodium system.
So, we will be looking to purchase a 400 High Pressure Sodium system.
Which Reflector Should I Get and Why?
The reflector is the most important part of a grow light. This will be the deciding factor in the amount of light reflected upon the plants and how uniform the light is. You want to have an even distribution of light over the entire growing area. Horizontal reflectors are the most efficient reflectors and are the most popular. A horizontal lamp position increases light up to 40 percent over a lamp burning in the vertical position. Smaller reflectors reflect light at a higher intensity because the light does not have to travel as far before it is reflected. Then you must factor in the size and shape of your garden. For those people who have a large garden with low light plants the larger reflectors may be a better choice. For our 3 x 3 garden with tomato plants we will go with a small reflector to get the maximum amount of light on the plants. Almost all of the lights we carry have air-cooling flanges and tempered glass as add-ons to your grow light. Air-cooling makes keeping your grow room cooler easy, by exhausting the heat emitted by the bulb before it escapes the reflector.
Here is a link to our Grow Lights page...