"growing plants taller than 12" before flowering is incorrect". Is this true???

"the actual light plants use is measured in PAR"


i said that earlier, im not arguing that the bluer the light the better for leaf growth, we all know that, i said in the long run the mh light is more convenient, efficient, and cheaper, in the long run babygro. i dont like arguing especially not with those who love to argue

babygro said:

Metal Halide bulbs which output so many lumens are measured using the light meaurement system the human eye can see, the actual light plants use is measured in PAR and as I mentioned HIDs output about 30% PAR light, so 30% of the total number of lumens output is the total PAR The plants actually use.

Click to expand...

Actually Babygro, ALL the lights we use in our hobby are rated in lumens. This is probably because we use these lights normally to see with.

With the broad "HIDs output about 30% PAR" comment, I thought you might be interested in these first two charts.

And finally the third charts shows efficiency amongst the various types of lights. As you can see by this chart, Babygro is correct saying fluorescents are cheaper to run.

they may indeed be cheaper to run, however i went from 158 watts worth of cfls to a 175w mh and noticed no change in my power bill, there may be a diff but its not very significant.

that 158W of CFLs will use the same amount of power as a 175W MH is the biggest bull i read tonight and if you would have figured what babygrow explained to you earlier a small MH can't compete with a number of CFLs using less or the same amount of power since the CFLs are closer to the optimum spec of the plant...

pastor420 said:

Actually Babygro, ALL the lights we use in our hobby are rated in lumens. This is probably because we use these lights normally to see with.

With the broad "HIDs output about 30% PAR" comment, I thought you might be interested in these first two charts.

And finally the third charts shows efficiency amongst the various types of lights. As you can see by this chart, Babygro is correct saying fluorescents are cheaper to run.

Click to expand...

single graphics are troubling you know pastor, if i go with with several sources as babygrow always does you will find several resolutes and you go with those that match the most of each other and normally you get them some info on how the test was set up, all this is laking here also most sources which been reliable to my understanding rated CFLs from 60 to 100lum/W and MHs from 45-120lum/W.

either way you will come across people who prefer to use mh and those who prefer cfls, some people use both.

DoobsDay said:

either way you will come across people who prefer to use mh and those who prefer cfls, some people use both.

Click to expand...

it is nothing wrong with using MH, really, but it is only worth the money if you have a big vegging room and use 400Wbulbs and bigger. then you get into the 110-120lum/W range with those bulbs and out-do CFLs. but below that a CFL is the more efficient way to veg with really

pastor420 said:

Actually Babygro, ALL the lights we use in our hobby are rated in lumens. This is probably because we use these lights normally to see with.

Click to expand...

I'm not sure what relevance this is Pastor420, I already stated earlier on that lumens is not a particularly good measurement for determining light that plants use because lumens is a measurement system for how much light the human eye can see - not what light spectrum plants actually use which is measured in PAR.

This is precisely why HID lights have such huge lumen outputs - a lot of the light spectrum they outout is in the wavelengths that plants don't use - for example in the yellow and green spectrum. This is why I said earlier - HID's have a PAR output of around 30%, that is - only about 30% of their total light output is in the PAR spectrum plants actually use.

pastor420 said:

With the broad "HIDs output about 30% PAR" comment, I thought you might be interested in these first two charts.

Click to expand...

Yes the charts are interesting, but are they supposed to be disproving something I said? Because they don't - they actually confrm it, if you're able to interpret the graph correctly. What the graph actually shows is the diminishing light intensity caused by the 'inverse square law' of single point light sources in comparison to the sun which is does not have the inverse squre law diminishing light intensity restriction - the suns light intensity is the same whether it's at the top of the plant or the bottom. So that chart shows how the PAR outputs of various wattage single point light source bulbs compare in intensity at various distances from the subject. What it doesn't tell you, is how much of those total bulb output percentages is actually PAR light - all it does is show you how much it increases the closer the light source gets to the subject. This isn't hard to prove at all aka -

400w HPS bulb outputs 55,000 lumens at 1 foot distance over 1 square foot. By my estimation only about 30% of those lumens will be in the PAR spectrum so 55,000 x 30% = 16,5000 PAR lumens. If we increase the distance of the light from the subject by one foot it changes as follows 16,500 divided by 2 foot x 2 foot = 4,125 PAR lumens. So a 400w HPS used at 2 foot distance will only actually output 4,125 PAR lumens. You can see why the output curves go up so sharply the closer the subject gets to the light.

If you read off the chart at 24 inches distance every single one of those light sources apart from the 1000w bulb are at or under 30%. If you calculate the proper distances each of those bulbs should be used at you'll find that pretty much every single one of them is outputting 30% PAR. Even the 1000w bulb when used at 36 inches which is about the correct distance is also outputting about 30% PAR.

Don't confuse the inverse square law with the percentage of total light output as PAR spectrum light.

[SIZE=-1]From what I remember from high school science class, though the visible light spectrum doesn't have real bounds it generally falls into the 400 to 700 nanometer range of the electromagnetic spectrum. The light we humans see is measured in variety of measurement units, such as lumen, foot-candles, lux, candlepower, etc.

Biology taught that plants use light for photosynthesis. The spectrum range that is useful to plants is referred to as PAR (Photosynthetically Active Radiation). This light falls into the 400 to 700 nanometer range of the electromagnetic spectrum. Plants use the full range, but to varying degrees. For example they use less in the 540 to say 620 nanometer range (green-yellow).

We were also taught that the entire electromagnetic spectrum, including light, is subject to Newton's Inverse Square law. This law deals with intensity and in regards to light it would[/SIZE] mean is that the lights intensity is inversely proportional to the square of the distance from the source. That means an object (of the same size) twice as far away, receives only ¼ of the energy. Because of this, intensity is usually measured in PFD (Photon Flux Density) which indicates how many photons per second per frequency per square meter are reaching an object [SIZE=-1](photons/s/nm/m^2)[/SIZE].

Recently I've learned that with plants this is called the PPFD (Photosynthetic Photon Flux Density) which makes sense being as frequency is part of the formula.

That's what I recall from school and what does it really mean? Not much. The bottom line is that the lights we use for our hobby are attempts to try and reproduce what the Sun supplies, which at this time of year is nearing 93 million miles away by the way. Even our "big" 1000W lights pale in comparison when you see that the "usable" light is only within 3-4 feet of the source. Our goal is to get as close to the real thing as our talent and budget allow in order to get the best possible crop. And that's what is really important here.

My intention was not to create trouble, only to make useful comments as to what I understand of the vast light topic. My sincerest apologies if I upset anyone.

It doesn't look like you have much lighting power.No point in growing plants that tall if you don't have the lighting to give to all the plant.If your growing plants over 3-4 ft you should have atleast a 6oo hps.Or even 1000 watts.It looks like your lights are low wattage so growing plants over 2ft are a waste.You should flower your plants when their short.There is no law in height when to flower.You can flower when your plants are even very small....6 inches even.I flower at 8 inches with thick stocks.I'm big on fans blowing the stocks right from the get go.This will help produce bigger buds once put into flowering.Depending on if the strain has more sativa verse indica,your plants should be around 2ft tall with fat ass buds.Try it.You'll see.But I suggest you get atleast a 400 hps to flower.Good Luck!!

pastor420 said:

[SIZE=-1]From what I remember from high school science class, though the visible light spectrum doesn't have real bounds it generally falls into the 400 to 700 nanometer range of the electromagnetic spectrum. The light we humans see is measured in variety of measurement units, such as lumen, foot-candles, lux, candlepower, etc.

Biology taught that plants use light for photosynthesis. The spectrum range that is useful to plants is referred to as PAR (Photosynthetically Active Radiation). This light falls into the 400 to 700 nanometer range of the electromagnetic spectrum.

Click to expand...

All good so far.

pastor420 said:

[SIZE=-1]Plants use the full range, but to varying degrees. For example they use less in the 540 to say 620 nanometer range (green-yellow).

Click to expand...

This is where you're going wrong - they don't use the yellow/green part of the spectrum. Ever wondered why plants leaves are green? Right, it's because of the chlorophyll in the leaves that REFLECTS green light - and that's why the leaves look green, that light is reflected and not used by the plants.

Nice lot of blurb about the inverse square law, but no comment on my comments on the charts you put up?

I like how Hearme's nice friendly forum got turned into this big arguement. I dont think either one of you is helping him out either, so I think if your going to post on his forum you should try and help him out a bit, instead of argue about lights. But while you guys are argueing, I got a light that is cheaper, and better then both. Sunlight My outdoor plants are lovin it, and the sun hasnt sent me an electric bill yet.

pastor420 said:

[SIZE=-1]From what I remember from high school science class, though the visible light spectrum doesn't have real bounds it generally falls into the 400 to 700 nanometer range of the electromagnetic spectrum. The light we humans see is measured in variety of measurement units, such as lumen, foot-candles, lux, candlepower, etc.

Biology taught that plants use light for photosynthesis. The spectrum range that is useful to plants is referred to as PAR (Photosynthetically Active Radiation). This light falls into the 400 to 700 nanometer range of the electromagnetic spectrum. Plants use the full range, but to varying degrees. For example they use less in the 540 to say 620 nanometer range (green-yellow).

We were also taught that the entire electromagnetic spectrum, including light, is subject to Newton's Inverse Square law. This law deals with intensity and in regards to light it would[/SIZE] mean is that the lights intensity is inversely proportional to the square of the distance from the source. That means an object (of the same size) twice as far away, receives only ¼ of the energy. Because of this, intensity is usually measured in PFD (Photon Flux Density) which indicates how many photons per second per frequency per square meter are reaching an object [SIZE=-1](photons/s/nm/m^2)[/SIZE].

Recently I've learned that with plants this is called the PPFD (Photosynthetic Photon Flux Density) which makes sense being as frequency is part of the formula.

That's what I recall from school and what does it really mean? Not much. The bottom line is that the lights we use for our hobby are attempts to try and reproduce what the Sun supplies, which at this time of year is nearing 93 million miles away by the way. Even our "big" 1000W lights pale in comparison when you see that the "usable" light is only within 3-4 feet of the source. Our goal is to get as close to the real thing as our talent and budget allow in order to get the best possible crop. And that's what is really important here.

My intention was not to create trouble, only to make useful comments as to what I understand of the vast light topic. My sincerest apologies if I upset anyone.

Click to expand...

thanks for the info

hearmenow said:

I read this on one of the other threads. I have 2 plants that are about 18". Should I be flowering already?

Click to expand...

you can flower at any time you like.

just put the plants under 12/12 lighting. Within a period of a couple or few weeks.. the plant will show its true sex to you. Once plant shows true sex, keep the females and cull the males.. leave the lighting at 12/12 schedule.. and within a certain amount of weeks (usually 7 to 14 depending on strain; Sativas have longer flowering cycles than Indicas) you will have a nice crop of beautiful buds.

good luck.

peace.