There is a full spectrum of Kelvin ratings of 3k, 4k, 6.4k, 10k, for the different stages of growth.

4K = Full Spectrum - SEEDLING / CUTTING

6.4k - Day Light - MAJORITY OF VEG

4K - Full Spectrum - LAST WEEK OF VEG

3K - Red Orange - MOST OF FLOWERING

10K - Uva Blue - FINAL WEEK

Does anyone run more than 2 distinctive light ratings at different courses of a grow?

Any advice on how to take full advantage of the growth stages?

Some people do. Some people use a Metal Sodium bulb, which is a bulb that has both a MH and a HPS filament in it. An example is the 600 watt Metal Sodium bulb and it puts off 300 watts of MH lighting and 300 watts of HPS lighting at the same time.

Others, like myself in the past when I was new to growing and limited on lighting would run both a MH and an HPS during vegging and then later went to my two HPS for flowering.

It is not exactly optimal conditions but then not everyone can create optimal conditions and some have to work within a budget and or work with what they have.

So you can mix/combine light spectrums but it will not be the very best of conditions. It will not be harmful but it could be better.

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The sun is around 5700-5800k.

Basically a decent 2700k and 6500k will overlap to produce a double spectrum peaking ideally for photosynthesis. Regardless of veg or flower.

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I run 2 x 400watt MH for veg and 2 x 400watt HPS for flower, but I was curious has to how much affect it would have if I:

added a 10k bulb the week of flowering?

I understand the spectrum mix, but how much benefit is the plant getting from the "perfect" extra light spectrum?


Facts like these interest me. I know all the basics about growing, but I enjoy the finer points.

Take a look at some of the charts in this thread question for light genius

Kelvin rating is merely an approximation of trying to match the color produced by an object called a true black body as it glows at that temperature. If you look at the black body line on that chart, you can see that it is only a small portion of the full color spectrum that is produced by the sun. You will also notice that the black body radiation color is just that, color, a human perception that doesn't matter to plants. Since UV light is invisible, there is no kelvin rating tied to UV and a 10,000K actinic will just be very blue and have no benefit for your plants.
Our bulbs, whether HID or fluorescent are not black body radiators and are a mix of various wavelengths. It is those wavelengths that are important as you can see in the photosynthesis chlorophyll absorption chart.

Kelvin or CCT ratings on bulbs are pretty worthless for our purposes except for the fact that vegging does require more 'blue' wavelengths and flowering needs added reds. But since you can have different bulbs with identical kelvin ratings with vastly different peaks and valleys at critical wavelengths, you will be seeing a trend to high PAR (photosynthetically active radiation) bulb ratings. GE already produces high PAR bulbs for the Horticulture industry and we are starting to see some hobbiest bulbs come out on the market too.