Light Intensity; LED vs HID

LED vs HID (THE GREAT DEBATE)

The intensity of hid is currently greater than LED due to the higher intensity at the beginning of the light itself. The inverse square law shows how all light doesn't diminish the same (linerally) instead light diminishes Logerithmacially just as sound does based of its intensity:


Meaning, the distance that a light source increases does not diminish the PPFD linearly with lights of different intensity. EXP: LED at 12 inches to 18 inches is only 6 inches of distance yet the PPFD diminishes from 940 PPFD to 445 PPFD a loss of 50% over 6 inches YET a Gavita 1000 watt DE at 24 inches to 36 inches is 12 inches while the PPFD diminishes from 1044 to 481 PPFD. a loss of 50% over 12 inches. This is a similar loss to the led but it takes the HID twice the distance to match the LED's greater loss.


Here are 2, 1 plant grow rooms for example:

Grow room 1 6 foot tall plant
A Gavita 1000 Watt DE at 24 inches above canopy, providing a center PPFD of approximately 1044 PPFD at the top colas, the lower colas 10 inches down are getting a PPFD of 500, which is great!

Grow room 2 6 foot tall plant
12 CXB 3590 at 600 watts at 12 inches is providing a center PPFD of approximately 940 PPFD at the top colas, the lower colas 10 inches down are getting a PPFD of 280 which is almost worthless
So you see the HID will crush the LED in this scenario.

It's all about cubic inches of ideal PPFD which I will say is 500-1000 PPFD

here's a new grow room using the sweet spots(500-1000PPFD) of each light in a sea of green:

A Gavita 1000 watt DE at 24 inches above canopy provides inside the 1 foot by 1 foot center square at a depth of 15 inches inside the 500-1000 sweet spot. outside the 1 foot by 1 foot square all the way to the 3 foot by 3 foot square there is an average of 5.5 inches of ideal PPFD depth. However outside the 3 foot by 3 foot square there is lower than ideal PPFD for flowering

total of 9,763 cubic inches of ideal grow space

12 CXB 3590 at 600 watts at 12 inches above canopy provides a nearly full 4 foot by 4 foot square of 940 PPFD yet only a depth of 16.5 inches, that's only 4.5 inches of ideal PPFD

total of 10,368 cubic inches of ideal grow space

So you see in this scenario the LED is pretty much equal to the HID light.

now we know we need more intensity with the LEDs. If we were to add a lens to magnify the CXB 3590, or we could also increase the power from 50 watts to 100 watts each but I don't have data for increased power.

So with the Ledil Stella HB Lens and 16 CXB 3590s at 50 watts each 15 inches apart we would have to move the LEDs to 18 inches from canopy otherwise we would get light burn or really Photon bleaching. so lets look at this set up

16 CXB 3590 at 800 watts 18 inches above canopy provides nearly a full 5 foot by 5 foot square of 1000 PPFD with a sweet spot depth of 7.4 inches

total of 26,640 cubic inches of ideal grow space! which is awesome for 800 watts

so to summarize HID is still king of huge colas on tall plants but it cant compete with today's sea of green short plants! the LED of tomorrow will have the intensity to maintain high PPFD at equal depths as HID and allow you to grow 6 foot tall plants....until that time comes stick with SOG for the more efficent but lower intensity of LED.....not to add in the heating issues of hid

Inverse square law light calculator:
http://www.intl-lighttech.com/support/calculators/calculator03

To find cubic ideal par area multiply width times length times depth based on your ideal PPFD from inverse square law calculator

light is light. treating an HID and a cob both as point sources of light, reflecting at a similar angle (say 90 deg with their respective reflectors) they follow the same relationship.

"The intensity of hid is currently greater than LED due to the higher intensity at the beginning of the light itself."

nope. not now that there are 500-1000+ watt cobs (citizen/flip chip/etc). you are making an assumption that HID is more intense than COB in all cases

put a 500W cob next to a 400W HPS and you would have the opposite relationship.

also regardless of whether it comes from one point or a multiple of sources like a cob array it will follow inverse square law

put 1000W of HID with a good reflector like an AC/DE and measure the intensity at 36"

take 700ish W of cob in the same setup (or whatever it takes to equal the same PPFD at 36")

measure the PPFD for both setups at 48" - it should be just about equal as the ratio of 48:36 is the same in both cases

if you took say 450W of cobs instead, and had to have it 12" off of the canopy to get the same canopy PPFD as the two setups above, and then measured it 12" lower than that, you would have greatly diminished PPFD relative to the two setups above because now your ratio of disance is 24:12

This is why i have said time and time again that "Penetration of (insert type of light here)..." is a complete and total myth. It has absolutely nothing to do with the source of the photons, rather the geometry of the light source relative to the top and bottom of the canopy.

hence the sun, which gives equal light to tops and bottoms of large plants, because there is near-zero difference between 93 million miles, and 93 million miles plus five feet.

of course in our indoor light study wall reflectance throws inverse square law out the window to an extent. if your room is adequately reflective enough, your photons will bounce around until they eventually land on your plant or get absorbed by other surfaces (the darker the more absorbance of course).

wanna have deep canopies? raise your lights as high as you possibly can and crank it up as high as you can just enough so as to not burn the tops. also leave space around the sides and between plants for light to get to the bottom. you'll be growing golf balls 12-24" below the canopy.

Raised lights isn't demished so much as spread further out.

Higher lights, more spread, lower lights, more penetration. With equal source light and beam angle.


Speaking of "penetration" why would we want to replicate gavitas when side lighting or under lighting is much more rewarding?

Atulip said:

Higher lights, more spread, lower lights, more penetration.

Click to expand...

not for a given PPFD at top of canopy. and why would you want it out of the 700-1200 range there?

BOBBY_G said:

not for a given PPFD at top of canopy. and why would you want it out of the 700-1200 range there?

Click to expand...

I never said any ppfd ranges. Just saying that a single point ppfd value "diminishing" by 53% isn't just disappearing, it's just being spread to a larger area.



OP post reads like light disappears when it's raised, or maybe I'm just really high. plus I wanted to chime in about under lighting and side lighting, equal ppf spread over a larger canopy surface is more efficient than a smaller canopy.

BM9AGS said:

so to summarize HID is still king of huge colas on tall plants but it cant compete with today's sea of green short plants! the LED of tomorrow will have the intensity to maintain high PPFD at equal depths as HID and allow you to grow 6 foot tall plants....until that time comes stick with SOG for the more efficent but lower intensity of LED.....not to add in the heating issues of hid

Click to expand...

sorry somehow you turned the inverse square law to conclude something that its not. bobby summed it up pretty well.
"deep penetration" through a plant canopy is based on a few basics.

- Same amount of light from as many different angles as is practical (ie side lighting, multiple smaller light sources, light movers etc).
- more photons, high intensity limited by how much the plant can tolerate. Photons are photons regardless of the source and the more the better.
- green/yellow wavelengths (light with a lower leaf absorbance is transmitted to the lower levels of a plant canopy).

BOBBY..... I think we're on the same page here

"light is light. treating an HID and a cob both as point sources of light, reflecting at a similar angle (say 90 deg with their respective reflectors) they follow the same relationship."

Light is light of course, it has no magical properties. you stated about the sun, yes clearly it's far far away thus inches here on earth does not change the PPFD metering. all common sense. this is exactly why LED is not as intense as HID(in our common practice here on Rui). We need the distance of 6 inches from canopy for a bare CXB 3590 at 25 watts to provide adequate metered PPFD. and with HID we need about 24 inches for the same metered PPFD. so the relation from the lights is not the same and does not scale together here in this instance. Just as the SUN does not scale the same at inches here on earth. so were saying the same thing generally

"The intensity of hid is currently greater than LED due to the higher intensity at the beginning of the light itself."

"nope. not now that there are 500-1000+ watt cobs (citizen/flip chip/etc). you are making an assumption that HID is more intense than COB in all cases"

I'm speaking from the perspective of what is currently in the market and the current market trend and that is a strong emphasis on under driving COBs for the great efficiency....when all you're achieving is less penetration. An under driven cob providing the metered PPFD of 940 at 6" means that 2.2 inches in to the canopy its measured PPFD would be at 500. so that's how the inverse square law is. with HID you need that 24 inches because of intense heat from IR and others but at least you're getting 15 inches of adequate PPFD! HUGE difference.


the whole point of my long post was to give some info on what to expect from LED and with the TREND of LED and its weak intensity at lower driven power it will shed light(get it 0 on why led is king of SOG and HID is still currently king of tall trees! Do you contest this??

put 1000W of HID with a good reflector like an AC/DE and measure the intensity at 36"

take 700ish W of cob in the same setup (or whatever it takes to equal the same PPFD at 36")

measure the PPFD for both setups at 48" - it should be just about equal as the ratio of 48:36 is the same in both cases

you are comparing apples to oranges here HID light SOURCE is about 5 inches by a quarter of inch inside the glass. so unless you can place 1000 watts of cobs in the size of the filament you cant compare and also cob users like myself usually place their cobs in a 12 inch by 12 inch or greater pattern! but of course if one were to increases the intensity of a LED to measure the same PPFD at 36' as the HID then of course they would be about the same... as i recall theirs a GLS quad array and the spectrum king lights that are similar to what your speaking and how are they doing? not so well!


if you took say 450W of cobs instead, and had to have it 12" off of the canopy to get the same canopy PPFD as the two setups above, and then measured it 12" lower than that, you would have greatly diminished PPFD relative to the two setups above because now your ratio of disance is 24:12

I think were saying the same thing here....... maybe I wasn't clear?!?! if you had an LED at 6 inches equaling 1000 PPFD then moved it 2x the distance to 12 inches you would have 250 PPFD where as with the higher intensity at the bulb of an HID you'd need to go to 24 inches to start at 1000 PPDS and at the same 2 x the distance to 48 inches would be down to 250 PPFD maybe i said something confusing! the distances are the key here with a led producing the same at 24 inches then yes it wold need 48 inches to meet 250 PPFD. Hmmm...one of my examples above was referencing actual PPFD measurements inside reflective surface....

in grow tents it doesn't scale exactly like the inverse square law because of reflection and what not but all of this is intended for the forum goers to get a grasp on the lights and how to best plan for their grow. its a tool and a nearly accurate one at that...side reflection is a bonus and by my math adds about 20% to the edges of any grow HID or LED on average.

BOBBY_G said:

all of the stuff you siad

Click to expand...

Atulip said:

I never said any ppfd ranges. Just saying that a single point ppfd value "diminishing" by 53% isn't just disappearing, it's just being spread to a larger area.

View attachment 3715107

OP post reads like light disappears when it's raised, or maybe I'm just really high. plus I wanted to chime in about under lighting and side lighting, equal ppf spread over a larger canopy surface is more efficient than a smaller canopy.

Click to expand...

For a single point metering it would be diminished.......but yes of course it's spreading. I sure the air eats some via humidity and particulates and whatever.....but nothing measurable in our environments.

Distance from canopy is still subject to desired spread.

IE stick your 20 x 25w(or whatever wattage to compare to hps) all inside your old hps hood in the center of a 4'x4' and it's going to require a 2 foot height to get the spread.

PurpleBuz said:

sorry somehow you turned the inverse square law to conclude something that its not. bobby summed it up pretty well.
"deep penetration" through a plant canopy is based on a few basics.

- Same amount of light from as many different angles as is practical (ie side lighting, multiple smaller light sources, light movers etc).
- more photons, high intensity limited by how much the plant can tolerate. Photons are photons regardless of the source and the more the better.
- green/yellow wavelengths (light with a lower leaf absorbance is transmitted to the lower levels of a plant canopy).

Click to expand...

I fixed one of my data bases that messed things up.

Yes I don't think you're saying anything that I'm not implying. As for side lighting and what not if you boxed cobs around a 6 foot plant it would crush hid. That's just single plant modified sea of green.....just the sea is shaped like the inside of a trash can.

These basis are off PPFD. So I have no clue of the green yellow penetration you speak of .....if it's not included in what a PPFD meter would calculate then it can't pe concluded in the base of my data. Sounds a little snake oil to me as PPF will measure yellow and green to what ever its mathematical value is for radiation.......no?

Atulip said:

Distance from canopy is still subject to desired spread.

IE stick your 20 x 25w(or whatever wattage to compare to hps) all inside your old hps hood in the center of a 4'x4' and it's going to require a 2 foot height to get the spread.

Click to expand...

Totally agree!!! But you still gotta factor in that if you used 1000 watts of cobs they'd be spread out where as the HID filament is all in one spot. So with all the cobs touching and say out to a 20 inch by 20 inch square it's not the same comparison.


I think people are getting wrapped around the axle and subjective that I'm in the led thread and have an example where his is better..... But that's only one example and who the hell would have a single plant under a 4 foot by 4 foot LED light that's under driven. That would be a waste.

So really I think we're all on the same page. At least I'm not seeing the difference here

BM9AGS said:

BOBBY.... you reference the inverse square law and also contend it in your thought process

"light is light. treating an HID and a cob both as point sources of light, reflecting at a similar angle (say 90 deg with their respective reflectors) they follow the same relationship."

Light is light of course, it has no magical properties. you stated about the sun, yes clearly it's far far away thus inches here on earth does not change the PPFD metering. all common sense. this is exactly why LED is not as intense as HID. We need the distance of 6 inches from canopy for a bare CXB 3590 at 25 watts to provide adequate metered PPFD. and with HID we need about 24 inches for the same metered PPFD. so the relation from the lights is not the same and does not scale together here in this instance. Just as the SUN does not scale the same at inches here on earth. so were saying the same thing generally

"The intensity of hid is currently greater than LED due to the higher intensity at the beginning of the light itself."

"nope. not now that there are 500-1000+ watt cobs (citizen/flip chip/etc). you are making an assumption that HID is more intense than COB in all cases"

I'm speaking from the perspective of what is currently in the market and the current market trend and that is a strong emphasis on under driving COBs for the great efficiency....when all you're achieving is less penetration. An under driven cob providing the metered PPFD of 940 at 6" means that 2.2 inches in to the canopy its measured PPFD would be at 500. so that's how the inverse square law is. with HID you need that 24 inches because of intense heat from IR and others but at least you're getting 15 inches of adequate PPFD! HUGE difference.


the whole point of my long post was to give some info on what to expect from LED and with the TREND of LED and its weak intensity at lower driven power it will shed light(get it 0 on why led is king of SOG and HID is still currently king of tall trees! Do you contest this??

put 1000W of HID with a good reflector like an AC/DE and measure the intensity at 36"

take 700ish W of cob in the same setup (or whatever it takes to equal the same PPFD at 36")

measure the PPFD for both setups at 48" - it should be just about equal as the ratio of 48:36 is the same in both cases

you are comparing apples to oranges here HID light SOURCE is about 5 inches by a quarter of inch inside the glass. so unless you can place 1000 watts of cobs in the size of the filament you cant compare and also cob users like myself usually place their cobs in a 12 inch by 12 inch or greater pattern! but of course if one were to increases the intensity of a LED to measure the same PPFD at 36' as the HID then of course they would be about the same... as i recall theirs a GLS quad array and the spectrum king lights that are similar to what your speaking and how are they doing? not so well!


if you took say 450W of cobs instead, and had to have it 12" off of the canopy to get the same canopy PPFD as the two setups above, and then measured it 12" lower than that, you would have greatly diminished PPFD relative to the two setups above because now your ratio of disance is 24:12

I think were saying the same thing here....... maybe I wasn't clear?!?! if you had an LED at 6 inches equaling 1000 PPFD then moved it 2x the distance to 12 inches you would have 250 PPFD where as with the higher intensity at the bulb of an HID you'd need to go to 24 inches to start at 1000 PPDS and at the same 2 x the distance to 48 inches would be down to 250 PPFD maybe i said something confusing! the distances are the key here with a led producing the same at 24 inches then yes it wold need 48 inches to meet 250 PPFD. Hmmm...one of my examples above was referencing actual PPFD measurements inside reflective surface....

in grow tents it doesn't scale exactly like the inverse square law because of reflection and what not but all of this is intended for the forum goers to get a grasp on the lights and how to best plan for their grow. its a tool and a nearly accurate one at that...side reflection is a bonus and by my math adds about 20% to the edges of any grow HID or LED on average.

Click to expand...

He was right, you are not. Go back and read the post you quoted again and try to comprehend what it says. Ie new cobs are around that are bigger than hid. Meaning there is more light on a smaller surface than hid.

Light is light and will disperse at the same rate, regardless of pretty much anything.

You have to start with the same amount of light though, not watts. Actual photon density. If you read and comprehend the previous post, it tries to explain this via the ratios and 1000 watt hid to 700 watt led.

Cobs are beating hids pretty much every way at this point. They put out more lumens/photons/light per watt, and are now making les that are even bigger that what hid offers. And with a 120 degree beam angle vs 360, you start with all your light in the right direction.

BM9AGS said:

I fixed one of my data bases that messed things up.

Yes I don't think you're saying anything that I'm not implying. As for side lighting and what not if you boxed cobs around a 6 foot plant it would crush hid. That's just single plant modified sea of green.....just the sea is shaped like the inside of a trash can.

These basis are off PPFD. So I have no clue of the green yellow penetration you speak of .....if it's not included in what a PPFD meter would calculate then it can't pe concluded in the base of my data. Sounds a little snake oil to me as PPF will measure yellow and green to what ever its mathematical value is for radiation.......no?

Click to expand...

Doesn't matter whether the plants are in a sea of green or as xmas trees, a well distributed light setup of smaller light sources (ie 50 watt cobs) will OUT perform and penetrate deeper better than a small single source of light (like a single 1K hid), at the same PPF.

you need to step back and think about what is really going on. Trying to duck behind ... some math that IGNORES absorption and transmission in a canopy is silly.

Well theoretically you could have your 1000w of diodes inside a bulb like hps. Emitting 360°.

My point being, light is light, no matter the source. If you've got 25w bare cobs spread out a foot apart then they should be 6" from the canopy. That's a pretty even spread over a square foot. If you've got a 1000w light source to cover a 5x5 you need that 3 foot hanging distance or whatever(calculated with beam angle and reflector spread pattern).


Edit: and better spread is definitely a thing. That's why I mentioned under lighting and side lighting before. A much better option than "just bombard the top with more light"

kmog33 said:

He was right, you are not. Go back and read the post you quoted again and try to comprehend what it says. Ie new cobs are around that are bigger than hid. Meaning there is more light on a smaller surface than hid.

Light is light and will disperse at the same rate, regardless of pretty much anything.

You have to start with the same amount of light though, not watts. Actual photon density. If you read and comprehend the previous post, it tries to explain this via the ratios and 1000 watt hid to 700 watt led.

Cobs are beating hids pretty much every way at this point. They put out more lumens/photons/light per watt, and are now making les that are even bigger that what hid offers. And with a 120 degree beam angle vs 360, you start with all your light in the right direction.

Click to expand...

If they're at the same intensity and distance yes.

But with an under driven led that needs to be 6 inches away from canopy to match 1000 PPFD it's only getting about 2 inches of penetration in the range of 1000-500 PPFD.

Where the hid needs 24 inches thus it's penetration is much greater. 10 inches of PPFD above 500

Are you saying this is incorrect???

BM9AGS said:

If they're at the same intensity and distance yes.

But with an under driven led that needs to be 6 inches away from canopy to match 1000 PPFD it's only getting 4 inches of penetration in the range of 1000-500 PPFD.

Where the hid needs 24 inches thus it's penetration is much greater.

Are you saying this is incorrect???

Click to expand...

I'm saying, you are the one comparing apples to oranges there.

Match light output, not wattage, and the light intensity will diminish in exactly the same amounts, as well as the same rate.

All light disperses at exactly the same rate. So if you stick the same amount of light in the same amount of space, it will spread the same.

What you're talking about is the difference between measuring a cob at 6" vs 12" against an hid at 24".

That doesn't make any sense.

Measure them both at 6" and then 12" and I bet the percentage of decrease is identical. It's a logarithm, and it's light. Light doesn't give a shit about our light sources efficiency, it just exists in the real world, and is treated the same by the environment regardless of its source.

Good luck putting a de 1000 6" from your tops though. Ppf would be insane, but your tops would also basically be on fire.
Sent from my iPhone using Tapatalk

BM9AGS said:

If they're at the same intensity and distance yes.

But with an under driven led that needs to be 6 inches away from canopy to match 1000 PPFD it's only getting 4 inches of penetration in the range of 1000-500 PPFD.

Where the hid needs 24 inches thus it's penetration is much greater.

Are you saying this is incorrect???

Click to expand...

yes that's incorrect, because to get the same PPF, you will need multiple smaller light sources.

Cobs are so "not intense at the source", they will burn through your clothing instantly.

PurpleBuz said:

yes that's incorrect, because to get the same PPF, you will need multiple smaller light sources.

Click to expand...

So you're saying this is incorrect:
under driven led that needs to be 6 inches away from canopy to match 1000 PPFD it's only getting about 2 inches of penetration in the range of 1000-500 PPFD.

Where the hid needs 24 inches to drop to 1000 PPFD thus it's penetration is much greater. 10 inches of PPFD above 500

I guess the online light square inverse law calculator is wrong.