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How cannabis cultivators measure and manage grow light radiation and spectrum

We have more choices today than we have ever had in terms of choosing lights for our grow rooms.

Generally speaking there are three phases to consider. Clone, vegetative (which includes mother plants) and flower/bloom cycles.

Depending on your style you can combine veg and flower phases using a single light spectrum. Growers have done this for years with high intensity discharge (HID) lamps such as HPS and MH lights.

Young clones are typically lit with much less light - florescent tubes has been a standard for years.

With the introduction of digital lighting - LED's. We now have the ability to provide our plants with a wide variety of spectrum which can not be produced by HPS or MH lights.

In the previous blog post we talked about spectrum and photosynthesis. We learned that plants in the veg phase prefer the "action spectrum" which includes more blue light and less red light wavelengths. We also know that plants moved down to the 12 hour cycle to induce flowering vastly prefer light in red wavelengths with much less blue and less overall light spectrum. This is mainly why grow lights appear purple in photographs or in some cases in person.

What this means is that todays grower's make a choice to either have two different lamps, one geared towards the Action Spectrum - a full spectrum grow light for vegging. And one geared towards flowering with a high peak in red wavelengths. Or, they can choose to use the same lamp and simply reduce the number of hours the lights are on when it is time to turn the plants to reproduction/flower phase. Growers who choose this second option make sure that they choose a light with full spectrum - and more important - they pick a lamp with a peak in red. Because without that peak of red light the final plant yield/weights will be lower. A lot lower. This is because during the flowering phase chlorophyll B becomes very important and as we saw in the last blog post - chlorophyll B demands red light and lots of it.

The second component of light which growers focus on is intensity. HID lights such as HPS have been the gold standard for many years. Growers focus on the total amount of Photosynthetic Active Radiation these lamps are able to produce. PAR is simply the total amount of light across the whole spectrum.