HPS vs. LED Grow Lights — Which is Better for Growing Weed?

Can we stop using the word "lux" please? Lux is for lumens. Lumens are for humans. Lux is biased towards the green area of the spectrum. Photons are photons and they can most definitely be counted! Far Red has very little weighting in terms of lumens (as in, no weighting at all!) and yet Far Red most definitely drives photosynthesis. So does UVA for that matter – again, not counted in lumens/flux.

You can also throw the Inverse Square law out the window because that only applies to a single light source. LEDs provide many sources of light from all different angles that are able to penetrate better than a single light source because . . .

. . . because nothing happens to a photon unless something gets in its way. It keeps travelling – from one edge of the universe to the other – until it interacts with something.

If you hold an open umbrella and I tip a bucket of water over you (HPS = single source of water) then most likely you will stay dry. But if I set spray nozzles all around you outside the protection of the umbrella (LED = multiple sources of water) and pump the same amount of water through, you are going to get very wet!

Is it that hard to understand why multiple sources of light offer better canopy penetration than singles sources? Leaves are like a bunch of tiny umbrellas – the only way to get through them is to go under or around them. Only a very, very small amount of light (mostly green and far red) penetrates the epeidermis of the leaf, and none-to-almost none penetrates through both sides.

hillbill said:

No

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Correct. I don't think he gets it. He forgets that leaves get in the way . . .

Prawn Connery said:

Can we stop using the word "lux" please? Lux is for lumens. Lumens are for humans. Lux is biased towards the green area of the spectrum. Photons are photons and they can most definitely be counted! Far Red has very little weighting in terms of lumens (as in, no weighting at all!) and yet Far Red most definitely drives photosynthesis. So does UVA for that matter – again, not counted in lumens/flux.

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I agree totally, but first I think we need to actually define lumen so people understand better.

1. the SI unit of luminous flux, equal to the amount of light emitted per second in a unit solid angle of one steradian from a uniform source of one candela.
   
   and That’s it, there’s no other definition.
   

Kassiopeija said:

Heeey oh how I love your red wig Prawn!!

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Does it freak you out that I'm a woman? Psst, it's actually pink

Prawn Connery said:

You can also throw the Inverse Square law out the window because that only applies to a single light source. LEDs provide many sources of light from all different angles that are able to penetrate better than a single light source because . . .

. . . because nothing happens to a photon unless something gets in its way. It keeps travelling – from one edge of the universe to the other – until it interacts with something.

If you hold an open umbrella and I tip a bucket of water over you (HPS = single source of water) then most likely you will stay dry. But if I set spray nozzles all around you outside the protection of the umbrella (LED = multiple sources of water) and pump the same amount of water through, you are going to get very wet!

Is it that hard to understand why multiple sources of light offer better canopy penetration than singles sources? Leaves are like a bunch of tiny umbrellas – the only way to get through them is to go under or around them. Only a very, very small amount of light (mostly green and far red) penetrates the epeidermis of the leaf, and none-to-almost none penetrates through both sides.

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Then please explain why we need to hang a rail type fixture closer to the canopy than an hps? Why don’t rooms with high bay hps just switch to rail lights hung at the same

Blue brother said:

I agree totally, but first I think we need to actually define lumen so people understand better.

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Blue brother said:

1. the SI unit of luminous flux, equal to the amount of light emitted per second in a unit solid angle of one steradian from a uniform source of one candela.
   
   and That’s it, there’s no other definition.

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No. We don't need to define lumen, because it has nothing to do with "radiant flux". Plants don't "see" lumens – they "see" photons and abosorb different spectra according to their pigments.

I should have quantified my plea to not use the term "luminous flux" (which you have been using) instead of just "lux" – my bad.

Luminous flux, or luminous power, is the measure of the perceived power of light. It differs from the measure of the total power of light emitted, termed 'radiant flux', in that the former takes into account the varying sensitivity of the human eye to different wavelengths of light.

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Blue brother said:

Then please explain why we need to hang a rail type fixture closer to the canopy than an hps? Why don’t rooms with high bay hps just switch to rail lights hung at the same

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Because high bay fixtures have overlapping light that strikes from different angles. A light mover moves the angle of incidence so that photons can go under and around leaves, penetrating the gaps in the canopy.

Please refer to my umbrella analogy.

If you hold an open umbrella and I tip a bucket of water over you (HPS = single source of water) then most likely you will stay dry. But if I set spray nozzles all around you outside the protection of the umbrella (LED = multiple sources of water) and pump the same amount of water through, you are going to get very wet!

Click to expand...

You will not immediately get as wet as a single dump of water over your head, but the combined power of those nozzles will make you just as wet had you not been holding an umbrella at all. That is the power of LEDs – they are able to hit the canopy at many different angles of incidence, which increases (vastly) the odds of each photon finding a gap to penetrate through.

Prawn Connery said:

No. We don't need to define lumen, because it has nothing to do with "radiant flux". Plants don't "see" lumens – they "see" photons and abosorb different spectra according to their pigments.

I should have quantified my plea to not use the term "luminous flux" (which you have been using) instead of just "lux" – my bad.

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my argument is that we can’t add up lumens from different sources because lumens by definition come from a single uniform source and that’s it. I’m not bashing leds or hps, I use both in different circumstances. Led more often than not! And if u read my earlier posts you will see that up until you chimed in I was the only person to actually speak about light coming from multiple angles and bypassing the canopy obstructions.
My point was simple, you can’t add lumens from different sources up because again by definition a lumen is a measure from one uniform source

Prawn Connery said:

Please refer to my umbrella analogy.

You will not immediately get as wet as a single dump of water over your head, but over time, the combined power of those nozzles will make you just as wet had you not been holding an umbrella at all. That is the power of LEDs – they are able to hit the canopy at many different angles of incidence, which increases (vastly) the odds of each photon finding a gap to penetrate through.

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I know this I said the same about 6 pages ago

Prawn Connery said:

Because high bay fixtures have overlapping light that strikes from different angles. A light mover moves the angle of incidence so that photons can go under and around leaves, penetrating the gaps in the canopy.

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Im not sure you have answered the question, why can’t we hang the rail light up in the same position as the hps? And expect the same growth at 3ft into the canopy?

Blue brother said:

Im not sure you have answered the question, why can’t we hang the rail light up in the same position as the hps? And expect the same growth at 3ft into the canopy?

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Not trying to be a dick, u obviously know ur stuff! So please, enlighten me.

Blue brother said:

...
My point was simple, you can’t add lumens from different sources up because again by definition a lumen is a measure from one uniform source

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That's preposterous

Sorry for turbo posting but I'm just responding to posts as I read them.

The idea behind light movers is not only to provide an even canopy, but to change the angle of incidence of the main light to allow better penetration through the gaps in the canopy.

This is exactly what happens in nature! The sun is almost never directly overhead – it traces an arc over the horizon and lights different parts of the plant as it moves.

OK, let's try this:

A coconut palm is on the equator. It is noon and the sun is directly overhead. The shadow on the ground is the same shape as the canopy. Only the top canopy is lit – the trunk of the palm tree is in the shade.

Five hours later the sun is on the horizon. The shadow has changed: you can now see an outline of the whole palm tree – canopy, trunk, coconuts and all! The sun is now lighting parts of the plant that were not lit when it was directly overhead.

So where did humans get the idea that you have to hang a light directly over the top of a plant?

Even when I grew with HPS, I never hung bulbs over the tops of my plants:



One of the same plants at harvest – note how thick it is all the way through.


Here's an even better example of side lighting:

Wow, i ate a burger and there's a whole page more

Blue brother said:

Right I’m following what ur saying, so when we use a rail type fixture we’re increasing the uniformity of intensity across the canopy?
but if we use a single source we’re increasing the intensity in the Center?
So if there’s more intensity in the Center would it not be fair to say that we are penetrating deeper into the canopy at that point than we would with multiple sources that all total the same power value?

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Kind of, but the single source could spread the evenly (in theory, and not taking counting shadows). What I'm saying is you got a bucketful of water and you pour it in your tent. How thick of a layer of water you get on the floor depends on the size of you tent. It doesn't matter if you pour it in from one spot or a hundred spots as long as it all ends up in the tent.

Blue brother said:

my argument is that we can’t add up lumens from different sources because lumens by definition come from a single uniform source and that’s it. I’m not bashing leds or hps, I use both in different circumstances. Led more often than not! And if u read my earlier posts you will see that up until you chimed in I was the only person to actually speak about light coming from multiple angles and bypassing the canopy obstructions.
My point was simple, you can’t add lumens from different sources up because again by definition a lumen is a measure from one uniform source

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You are being dogmatic. Your lumen argument really has nothing to do with the best way to grow plants. I'm sorry, but until you can get past the dogma of semantics, you will not see the light (pun intended).

Horselover fat said:

Wow, i ate a burger and there's a whole page more




Kind of, but the single source could spread the evenly (in theory, and not taking counting shadows). What I'm saying is you got a bucketful of water and you pour it in your tent. How thick of a layer of water you get on the floor depends on the size of you tent. It doesn't matter if you pour it in from one spot or a hundred spots as long as it all ends up in the tent.

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Agreed

Prawn Connery said:

You are being dogmatic. Your lumen argument really has nothing to do with the best way to grow plants. I'm sorry, but until you can get past the dogma of semantics, you will not see the light (pun intended).

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My lumen argument wasn’t bashing leds or you or anyone for that matter, someone posted and said you can add lumens up, I replied and said that’s not possible. That’s it, somehow in the process of explaining why, I’ve been put in the corner with the troll. Now getting posts from so many other people going on as if I’m saying hid is better than led, which it’s not! Multiple sources that deliver the same amount of photons to the canopy =BETTER. I agree with that, I’ve been saying that since the start of the thread

Some already expand current PAR charts on each end for deep/far red and UV, neither is even counted now. We can’t see them and lumens are really not relevant here.