How much light does a budding plant need?

[Aweedtec]

Why is this not a question answered anywhere?

How many MOLS? Like if you use Photone. How many Mols are necessary to bud? Like....can I turn my lights down from 100,% and still get the same results? If so how much? Distance?

My light is 500w of 281 Samsung's. Just over 1000 LEDs per light. They are 1w LEDs turned down to .46 each at 100%

I'm asking this question because i would like to save some money. Electric bill is doubled from three 500s going 12h a day

 

[Sativa1970]

There is no one answer because there are too many variables. Size of light, room, plant, genetics, and environment all have an effect on how much light a plant can use. Flowering and veg stage effect light needs. The absorption of light to yield is not linear but a curve.

There are some general guidelines that may help answer your question. You need a minimum of 13wats/ square foot for healthy growth. Bud production increases exponentially up to 20wats/ square foot. You will see a lesser but significant increase in yield and quality up to 25wats/ square foot. From 25-30wats per square foot you will have marginal gains and over 30 wats you move into an unnatural environment to utilize the light such as added CO2.

You are using 1.2Kwh per day with that light on 12 hours 100%. You can look at your local rate but the average is 12 cents US per Kwh. or $4.32 a month. Unless you are extremely over lighting or large scale, cutting back it isn't worth the loss in yield and quality.

 

[Delps8]

Roughly speaking, as much as you want to give it.

Research demonstrates an almost linear relationship between increasing light levels and increase in crop yield and crop quality.

I've attached one paper on this topic - there are many more, documented and peer reviewed,

Here's a table I've created based on the data in the paper:

The change in yield ("∆ %") is significant - increasing just 200µmol resulted in about a 20% increase, thought the delta did diminish as PPFD increased.

The reason for this is simple - light is required for photosynthesis, which is how plants make food (nutrients are not food). The more photons, up to 800-1000µmol ±, the more food that plant can make. Even without adding CO2, cannabis will thrive at 1kµmol, assuming that the grow is in good shape. These are the light data from my current grow, as of yesterday:

I'm taking nine samples using an Apogee PAR meter.The grow has been between 900 and 1kµmol for weeks (the grow is in day 64 or week 9.1).

In contrast, the economic benefit is dependent on a variety of factors. To figure out if it's economical is "cost accounting" and can be very simple or quite complex. I worked in accounting in my first job out of college so I'm not unfamiliar with what's involved.

Here in Southern California, electricity is among the most expensive in CONUS but the cost of weed is also very, very high so the cost benefit is there, even at 45¢ per KwH. If I (still) lived in Colorado, where weed is cheap, I would never have started growing my own.

On the light level question - it really is dependent on how much you want to spend. If your electricity rates have peak hours, you might want to avoid those and you can change your lights out time so that you don't have to run a heater, for example. Taking steps like that can help reduce cost but cannabis growing indoors requires a lot of electricity.