More lumens please

When growing pot, the more light you have per square foot, the more plant you will get. This is a scientifically proven fact, and it makes sense.
There are four standard lighting options: fluorescent lighting, mercury vapor lighting, metal halide lighting, and high pressure sodium lighting. Each has its own pros and cons based on intensity of light (measured in lumens), heat, and spectrum of color.

Here’s an overview of how to choose and use the best method for different stages of growth.


Fluorescent lighting is a very efficient way to light a large space like an office building. For growing, however, it isn’t the best option, as it isn’t very intense for the amount of power it sucks up. A fluorescent bulb at 40 watts will only put out about 3,000 lumens. And even with many bulbs in use, fluorescent lighting isn’t the right choice for the later stages of growth.

However, for the first stages of growth, ? rooting clones or seeds ? it is excellent because it is a soft and gentle lighting source that generates very little heat. Clones will thrive under the light of a bank of gentle fluorescent bulbs until the roots take or new growth sprouts from the top of the plant. Then the clones should be put under a more powerful light source.

Keeping clones under fluorescents for too long will cause the plant to become phototropic. A phototropic plant is one that has expended all of its energy in attaining height to reach a weak light source. The space between the leaf branches (the internodal space) will be large, and the plant will be feeble.

Newly rooting clones do not need the same light intensity as plants in the green growth stages. Putting rooting clones under the full radiance of a metal halide will kill them, slowly. The intensity of light and heat will dehydrate the leaves since a clone doesn’t have roots to suck up more moisture. This won’t be apparent at first because the foliage will actually grow well. What won’t grow well, though, is the roots.

Subtle fluorescent lighting is great for clones as the rooting process is dependent on a specific pair of hormones. That is, the levels of each of these hormones determines the speed of root growth. While under intense light, the plant will want to take advantage of this intense level of light and speed up the growth of foliage. Since there’s only a finite amount of energy that can be put into growth in total, the hormones that determine the speed of root growth aren’t generated in normal amounts. This translates into fairly slow root growth.

While the clone is under intense light, the roots won’t grow fast enough to support the plant that is sprouting so much green foliage. The roots cannot keep up, and the plant will eventually starve itself under the nutritional needs of the foliage.

A good level of lighting for rooting clones or seedlings is around 1,500 lumens per square foot of grow space. A fluorescent bulb is about four feet in length and puts out 3,000 lumens. The effective reach of the light is about one foot. So two of these bulbs, totalling 6,000 lumens combined, would be appropriate for a grow area of four square feet.

For more clones, adding pairs of double-bulbed light fixtures will double the clone rooting area as needed.