When a beam of normal white light is split with a prism it is possible to see all of the different colour bands it is made of. These colour bands are the colours of the rainbow; when you see a rainbow you are seeing sunlight being split by the rain. These bands correspond with frequencies given off by the heated light source.

So how is this relevant to your grow?  Well, different lights have different effects on how your plants grow. The light bulb's colour can give a good indication as to which factors important for plant growth are present within the light.

The colour a light emits can be related to the bulb's Correlated Color Temperature (CCT), often expressed in degrees Kelvin (K). When you know the K value of a bulb, you will get a good feeling of what effect it will have on your plant.

The following brackets should give you a solid indication of what to expect from different CCT levels (expressed in K):

1,500-3,000 Kelvin: Bulbs of this CCT level tend to be dark orange or red in colour. They help promote flowering.

3,000-3,700 Kelvin: Bulbs of this CCT level are yellow/neutral in colour. They cause high rates of photosynthesis throughout all stages of cannabis growth.

3,700-4,000 Kelvin: Bulbs of this CCT level are a warm neutral colour. They encourage rapid growth.

4,000 Kelvin: You will find that a lot of bulbs of this CCT level are standard, neutral white. They cause a cannabis plant to grow normally.

4,000-5,000 Kelvin: Bulbs of this CCT level are light blue in colour. They help promote good leaf and stem growth.

5,000-8,000 Kelvin: Bulbs of this CCT level are a deep blue colour. They help promote outstanding leaf and stem growth.