Growers’ Circle

How to Choose your Lighting

By Dr. Who

Lighting is one of the most important aspects of indoor growing. There are so many different kinds that it can be very confusing. The most common types are HID (High Intensity Discharge), fluorescent and compact fluorescent. Today, we’ll be discussing HID lighting.

HID lights are the most common type of indoor plant lighting. The two major types are high-pressure sodium, which gives off a reddish-orange light, and metal halide, which gives off a whitish-blue light. Both are available in many different wattages, with 1000w, 600w, 400w and 250w being the most popular. The wattage determines how large an area your light can cover, and also the amount of light penetration they will provide.

Metal halide (MH) lights are normally used for the initial vegetative growth of plants. Plants seem to respond to a whitish-blue light during the early stages. They tend to produce a more compact, shorter plant with tighter internodal lengths (the distance between the branches on the stem of the plant). This is very important to indoor growing, because if your plants “stretch” too much during the vegetative growth stage, they end up too tall and lanky during the flowering stage and do not produce the quantity of buds that a shorter, tighter plant will produce. One thing to keep in mind is that two-thirds or more of the ending height of your plants is done during the flowering stage, so keeping your plants short during vegetative growth is a must. You want to keep your plants under a MH light until you switch to the flowering stage (cutting the lights back to 12 hours on, 12 hours off).

A high-pressure sodium (HPS) light is the best HID light to use during the flowering stage. Plants have been shown to respond with larger yields under reddish-orange light, which mimics the fall sun. HPS lights put out more lumens per watt than MH lighting, and are therefore more efficient. Some growers believe that you can run an HPS light throughout the entire cycle with no ill effects on the plant. I prefer to use both types.

An HID light consists of three parts: the ballast (which is a transformer that changes the power from the wall outlet to a form that the bulb needs to light up), the bulb and the reflector. The ballast of a 1,000w light (the most common) can weigh up to 40 pounds, depending on the type of ballast that you choose. The older type, called Core and Coil ballasts have been used for many years. They are not very efficient, but they work very well and are extremely reliable. The newest type, the Digital Ballast, is the latest and greatest. They provide up to 30 percent more light with the same power usage as a Core and Coil ballast. In the past, Digital Ballasts have not proven to be extremely reliable, but the newest ballasts on the market are showing exceptional promise. A 1,000w Digital Ballast can weigh as little as 6 pounds. They can run either MH or HPS bulbs, so they are very garden-friendly. They should displace Core and Coil ballasts in the next few years.

There are many different kinds of bulbs on the market. I prefer to use the most inexpensive bulbs, as the “plant-specific” bulbs that are available do not give a noticeable increase in yield or light output. The most important thing to remember about HID bulbs is that after six months of use, the light output goes down dramatically—up to 25 percent. You should replace your bulbs every six months or so.

As with bulbs, there are many different kinds and types of reflectors on the market which prove reliable and put out an excellent spread of light. Do your homework to find your right fit, or just email me for advice.

DR. WHO is a Southern California expert in plant cultivation. Reach him at drwho@freeculturemag.com.

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