Light Intensity Explanation For EVERYONE

I'm going to attempt to make this as simple as possible because too few people understand the concept of light intensity. Unfortunately, I'm not going to make any diagrams. Perhaps someone will be willing to make some and put some up using this explanation, but I will not. I'm also going to make up my own unit of light called a "Light Unit" because i am not up for calculating "lux". It is the same exact thing as "lux" only I am using different measurements. Just like kilograms and pounds measure the same thing, i'm going to use "Light Units" instead of "lux"


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The Basic Math

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Suppose you have a 150w HPS giving off 15000 lumens. Any plants:

1ft away receive 16 Light Units
2ft away receive 4 Light Units
4ft away receive 1 Light Units

This shows that an object 2x the distance away receives 1/4th as much light. This is because light intensity decreases by distance squared. An object 4ft away from a light receives 1/16th as much light.

Now, Suppose we have a 600w HPS giving off 16000 lumens. Any plants:

1ft away receive 64 Light Units
2ft away receive 16 Light Units
4ft away receive 4 Light Units
8ft away receive 1 Light Units

This is exactly true... 4x as many lumens = 4x as much lux/"Light Units" for a given distance.

Now, using this shown concept this means any plants under a 150w HPS will receive JUST AS MUCH LIGHT as any plants 2x the distance under a 600w HPS.


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A Design Concept

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This means that plants 1ft under a 150w HPS get just as much light as plants 2ft under a 600w HPS.

Plants 2ft under a 150w HPS get just as much light as plants 4ft under a 600w HPS.

This means that if our ideal growth area under a 150w HPS is no farther than 2ft away. The ideal growth area under a 600w HPS is no farther than 4ft away.

No ifs, ands, or buts. THIS IS FACT. If you believe that buds grown 2ft from a 150w HPS are the smallest you accept, then buds grown any more than 4ft from a 600w HPS will be smaller.


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Some Practical Application

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Now, suppose that we don't want our plants any more than 1ft from our lights (heat stress).

This means that we have between 1ft and 2ft underneath a 150w HPS to grow ideal buds. However, we have between 1ft and 4ft underneath a 600w HPS to grow buds.

This is where everyone says having more "light intensity" matters. The 600w HPS gives off light that is capable of "stretching" a greater distance. We have 2x as much area to grow ideal buds (between 2ft and 4ft underneath). We ALSO have between 1ft and 2ft away to grow buds that are receiving MORE light than could be possible under a 150w HPS (due to heat stress).

If you wanted to grow the same buds grown 1-2ft from a 600w HPS. You would have to grow buds between 6-12 inches from a 150w HPS.


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Fluorescents DON'T Suck... Much

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Fluorescents follow the exact same rules. Buds grown 1ft from 10 1500 lumen CFLS are exactly the same as those grown 1ft from a 15,000 lumen HPS or 2ft from a 60,000 lumen HPS.

Here is the advantage CFLs have:

at 6 inches those CFLs have the same intensity as a 150w HPS at 6 inches or a 600w HPS at 1ft

at 3 inches those CFLs have the same intensity as a 150w HPS at 3 inches or a 600w HPS at 6 inches

at 1 inch those CFLs have the same intensity as a 150w HPS at 1 inch or a 600w HPS at 2 inches. (This is however impractical for HPS lights unless they are cool-tubed, it is not a problem at all for fluorescents though)


CFLs are capable of providing just as much light to plants(even more in some circumstances) as HED lights because they may be placed so close to the plants. This is why they are excellent for vegging. HOWEVER, their intensity is very low which is why they are horrible for flowering. Their light cannot "stretch" as far as HPS lights. Where as you may get excellent buds up to 4ft away from a HPS (which also means covering a large area), you would have to keep the buds no farther than 2ft from all of the CFLs for the same results.


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The Point

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ALL LIGHTS are capable of creating the same buds. However, the more lumens that a light gives off, the farther away buds of a decent size will grow. This is why CFLs aren't ideal for budding.

10 1500 lumen CFLs can produce the same buds between 6-12 inches away as a 60,000 lumen HPS can produce 1-2ft away.

1-2ft away from 10 1500 lumen CFLs is the same as 2-4ft away from a 60,000 lumen HPS.

In the end, even though CFLs don't have to worry about heat stress... they are still only really capable of producing 2ft deep of buds. That 600w HPS is capable of producing 3ft deep of buds (3 1/2 ft deep if cool-tubed).

So next time you say CFLs suck, keep in mind they are just as capable of producing excellent buds as HED lights, only in smaller quantities because of few bud sites can be placed next to the lights. For Vegging, they are practically ideal because of how close they can be placed to the tops of the plants to prevent stretching.

Also keep in mind, any buds grown more than 5ft from a 1000watt HPS will be just as small as any buds grown farther than 2ft from a 150w HPS or 4ft from a 600w HPS...

I don't think this explained it very well, sorry man. I couldn't do better, thanks for the info.

Nice post. Inverse square law can be your friend or enemy.

This post is oversimplified, and the information is biased towards CFLs. The main thing you neglected to mention is that HPS are far more efficient, and therefore put out more light for every watt used. This is even more true of the higher wattage HPS, which makes many of your comparisons between the 150 and 600 lights inaccurate.

You would need over 1200 watts of CFL light to equal the 600 HPS, in terms of light output.

There are other factors to take into account, such as PAR, intensity and spread of many vs 1 light etc., but the fact remains that HID's are generally a better choice, particularly when your grow is consuming more than a couple of hundred watts, or your grow space is more than a couple of square feet.

CFLs have their place in small grows, or in areas with particularly limited height, but in most cases, HIDs are the light of choice if you want to yield well.

great info! I wanted to point out that these figures would be for an "empty" area with nothing blocking the orginal light source(s). I could never see my self using a single light source no matter what the circumstances, simply due to the fact that multiple light sources will always have better "penetration" due to objects being in the way creating shadows. Shade is shade and equates to less light, no matter how intense a light source is.

this is a bit to basic but like seing people ideas and thoughts on growing/lighting nice.

This isn't biast to CFLS... its indicating that fluorescents can give buds just as much as HID and that distance plays a big factor. I never said you need the same wattage, I only said the lumens don't make a difference where they come from as long as they are the same total. The title says "Light Intensity" not "CFL watts".

And I made some typos anyway... the point is that if you have 50,000 lumens of fluorescent and 50,000 lumens of HID... the fluorescent will yield just as well, only in a more limited area... and even better in the aspect that the light comes from multiple angles and penetrates even better than HID. Just as GROW1620 said.

You repeatedly mention specific wattage lights in your comparisons, without taking into account that the higher wattage HID lights are far more efficient in terms of lumens per watt, making your following statements untrue:

Redeflect said:

Now, using this shown concept this means any plants under a 150w HPS will receive JUST AS MUCH LIGHT as any plants 2x the distance under a 600w HPS.

Click to expand...

Redeflect said:

This means that plants 1ft under a 150w HPS get just as much light as plants 2ft under a 600w HPS.

Click to expand...

Redeflect said:

Plants 2ft under a 150w HPS get just as much light as plants 4ft under a 600w HPS.

Click to expand...

Redeflect said:

No ifs, ands, or buts. THIS IS FACT. If you believe that buds grown 2ft from a 150w HPS are the smallest you accept, then buds grown any more than 4ft from a 600w HPS will be smaller.

Click to expand...

You also use these specific wattage lights when comparing to cfls, thus giving a false impression of their capabilities vs various hid lights. Since your post is called "light intensity", you should definately cover the fact that higher wattage HIDs are more intense than lower wattage ones, or just don't mention wattage at all, and keep your info purely lumen based.

Don't get me wrong, I understand the spirit of your post, and I agree that CFLs can grow good buds. However, people should have as much information as possible before chosing a suitable light for their grow. CFLs are great for first time growers, micro grows, or for areas with very limited headroom, but in most other situations, HIDs are generally a better choice.

i thought it was pretty good a few flaws for things not taken into consideration but pretty good nevertheless