Kelvin - A little light on the subject.

I'm sure there have been a few threads explaining a little about Kelvin, but I thought I'de confine the information into one area, expand on it a little, and go into some more detail.

Here's a little information on Kelvin, from what I know:

Kelvin temperature is a numerical measurement that describes the color appearance of the light produced by a lamp and the color appearance of the lamp itself, expressed on the Kelvin (K) scale.

The science behind determining color temperature values starts with the theoretical black body radiator, a block of black metal through which electric current is passed (performed as a computer model). As the metal is heated, it turns red-yellow, then white, then blue; as the temperature of the metal is measured at any given color produced, we then match the color to that temperature and a color temperature value is determined.

Ok so how does this apply to lighting and Cannabis?

Well, the Kelvin temperature is used to categorize lamp lighting as warm, neutral or cool sources. The terms are not directly related to temperature; instead, they describe how the light source appears visually.

Warm sources actually have a lower color temperature (3500K or less), producing a red-yellow appearance. Neutral sources (between 3500K and 4100K) tend to have a yellow appearance. A lamp with a color temperature of 5000K is considered pure white light (Full Spectrum) with the lamp becoming more blue in color as the color temperature is increased.

Now Cannabis will survive in a pretty wide range of Kelvin. The thing we have to remember is that there is a small range of both the warm and cool spectrum that plants in gengeral utilize for photosynthesis. Most plants cannot see the other spectrums. So it's important to give your plant the right spectrums of light during ALL stages of growth to achieve maximum photosynthesizing energy.

Also in regards to money, electricity and efficiency, it's best to focus on the Kelvin range that is used most by the plant to utilize your light more efficiently.

Which Kelvin range promotes the most efficient photosynthesis energy is debateable but here is a general idea of how it works:

5K - 7K Kelvin:
Promotes bushy growth. Ideal for rapid growth phase of plants.
Greatly enhances all-around plant growth when used with super
high output, high pressure sodium or 3K warm metal halide lamps.

4.2K - 4200 Kelvin:
Can be used as supplimental blue lighting when used with a 3K
source.

4K - 4000 Kelvin:
Best single source for plant growth, producing shorter, bushier
growth than 3700 Kelvin and color rendition. Used in general
plant lighting.

3.7K - 3700 Kelvin:
This coated lamp is used in general plant lighting and for more
rapid growth than 4000 Kelvin produces.

3K - 3200 Kelvin:
Highest photosynthetically active radiation (PAR) value of all HID
lighting for all phases of plant growth. PAR watts account for the
nutritional value of light and are a direct measure of the light
energy available for photosythesis.

2.7K - 2700 Kelvin:
Redder color mix, used for propagation, blooming, supplemental
greenhouse lighting.

I hope this will be of some help and finally shed some light on the subject. ;)

I always wondered but never got around to looking it up. Thanks.:)

as far as the kelvin scale is concerned I've found that the hortilux bulbs with the enhanced blue spectrum are about the best single bulb you can get...other bulbs have similar spectrums and probably work about the same...to get better lighting you'd have to have a double bulb or use 2 lights but I find just the wide spectrum horti grows tight nodes and hairy buds so I've never really looked much further...

Overall a mh with a higher blue content is better for veg growth and you might see a slight advantage over hps and hps for flowering and if you use both mh like a 400mh with a 600hps you should get a pretty even spectrum from seed to cure

Par is more important than total lumens...a 100k lumen bulb could outperform a 150k bulb if the par is higher...

a general rule is mh for veg and hps for flower as the blue promotes stem/leaves and the hps promotes bud/flower

hps throughout the grow is decent

hps with enhanced or wide spectrum (added blue) is better

mh for veg and hps for flower is better still

and the best is both mh and hps throughout....ie 400mh and 600hps

I've used a 400w hps hortilux bulb with great results so if you are only going to use one light I'd recommend a wide spectrum hps :jointsmile: