Lighting Bilbo's Brief Guide to Choosing Your LED.

[HubbaBubba]

keep it civil.

Yes please, this is the best discussion of lights that I have found so far.
It is a controversial topic, so there will be lots of heat, lets make sure there is some light too.

Where can I find a chart/graph comparing PAR/watt efficiency for various lights: incandescent, induction, florescent, LED, HID, HID double ended...

 

[A4]

Yes please, this is the best discussion of lights that I have found so far.
It is a controversial topic, so there will be lots of heat, lets make sure there is some light too.

Where can I find a chart/graph comparing PAR/watt efficiency for various lights: incandescent, induction, florescent, LED, HID....

That my friend is a tricky thing to do, there is no one chart that I have found. PAR meters are pretty pricey so you won't find most average growers keeping them on hand. To boot, lighting manufacturers have just recently started putting their data out.

This isn't advertising for any one site but in full disclosure I have purchased from them several times. http://growershouse.com/blog They have a blog called "Review Lab" where the guys test all kinds of products. You can also find them on https://www.youtube.com/user/GrowersHouseHydro with a lot of information. I don't work for these guys and have no vested interest in their company, I just really really like their testing. They are thorough and accurate. Hopefully this helps you some in your endeavor.

 

[HubbaBubba]

What about PWM (Pulse Width Modulation) for LEDs. Can the Pulses be timed so that chlorophyll can synch up with the pulses and save electricity in between? How long is Chlorophyll's refractory period, and can LED's respond faster?
That would really mess up the PAR measurements.
Yup, I don't know what I am talking about, just asking, here to learn.

 

[A4]

What about PWM (Pulse Width Modulation) for LEDs. Can the Pulses be timed so that chlorophyll can synch up with the pulses and save electricity in between? How long is Chlorophyll's refractory period, and can LED's respond faster?
That would really mess up the PAR measurements.
Yup, I don't know what I am talking about, just asking, here to learn.

Oh, now you are talking my language, lol. Are you an electrician?

It would probably take some capacitance to dampen the load going to the LED modules and you would probably be looking at using MOSFET or IGBT like in a high frequency drive. I can see the possibilities to cut electrical usage down some, but it would be very dependent on photosynthesis in the plant and at what rate there were diminishing returns. I would be willing to bet no one has ever looked at that because I assume it would take a biologist to determine that and I can't imagine one caring enough to put any thought into it. Maybe I am wrong? Could be some that are dedicated to growing under lights but I have yet to see any that devote a lot of time to it.

Honestly I don't know if it would be marketable because what are you looking at saving? Maybe a few watts per hundred? Even in a thousand watt system there isn't that much savings. It is a helluva an idea though.

 

[blue]

You beat me to it A4

@Spank - thats not the way we do things here. I've read your 5 posts and 2 of them are mean.
Please be nice or i'll need to ban you.

 

[TaNg]

Because most LED manufactures use different spectrums can PAR be misleading?

Let's say I have 2 300w grow lights, one light with a poor spectrum for photosynthesis and a light with a highly effective spectrum for cannabis cultivation, both lights use the same quality components. Obviously grams of weed per watt would be reflected in the effectiveness of the spectrum but would PAR readings reflect this or could only field tests reveal this? I suppose my question is can PAR meters tell how affective a spectrum will be or do they just tell you how many photons are avaialable between 400-700nm?

 

[A4]

Because most LED manufactures use different spectrums can PAR be misleading?

Let's say I have 2 300w grow lights, one light with a poor spectrum for photosynthesis and a light with a highly effective spectrum for cannabis cultivation, both lights use the same quality components. Obviously grams of weed per watt would be reflected in the effectiveness of the spectrum but would PAR readings reflect this or could only field tests reveal this? I suppose my question is can PAR meters tell how affective a spectrum will be or do they just tell you how many photons are avaialable between 400-700nm?

Leave it up to the LED master to make me look at things completely differently. Not to put words in your mouth but in other words, something like the holy grail of spectrum. You know more about this than I do TaNg, and it shows because after looking at that question for a minute and researching. It looks like you are correct. My guess, you knew the answer before you asked the question, lol.

Here is where my ignorance shows because I am no biologist. When I have been looking at lights I always thought PAR = PAR. Now, looking at the chart and I see that PAR is a broad range of 400 - 700 nanometers and that everything in that spectrum will register at PAR. So, when I looked at the chart, it looks like everything from ~500 to ~630 is less efficient than the remainder. That is quite a major amount of the PAR range. 400-700 is 300 nanometer range and 130 nanometers(the 500-630) is almost half of that entire range. So yeah, one could be entirely in the same spectrum and still only be half as efficient as one that is perfectly tuned.

Screw me, that makes me look at things from a different perspective. So, PAR ≠ PAR. Thanks for chiming in bro!

 

[Xagor]

Hey A4,
those diagramms are widley spread, but unfortunately they are wrong.
This is where all this red/blue for led comes from.

What this diagram shows is a chart for the algae ulva or pigments in a solution.
But not plants.
Looking at actual leaves it looks totally different.
Take a look here:
you will find algae ulva and crop plants in the same chart in figure 9.
http://www.photobiology.info/Gorton.html



This study explains why green is so nice for plants and the mechanisms behind it.
Even though it seems counter intuitive bc plants are green and so must reflect more of it -its actually intended by nature and more or less a clever trick.
http://pcp.oxfordjournals.org/content/50/4/684.full

edit,
regarding that spectrum is not that important you can find this study:
"There is considerable misunderstanding over the effect of light quality on plant growth. Many manufacturers claim significantly increased plant growth due to light quality (spectral distribution or the ratio of the colors)."
[...]
"Over the past 30 years, numerous longer-term studies with whole plants in higher light indicate that light quality has a much smaller effect on plant growth rate than light quantity [6], [7]."
[...]
"The effects of light quality on fresh or dry mass in whole plants typically occur under low or no sunlight conditions, and are caused by changes in leaf expansion and radiation capture during early growth [6]."

and a little shocker:
A widely used estimate of the effect of light quality on photosynthesis comes from the Yield Photon Flux (YPF) curve, which indicates that orange and red photons between 600 to 630 nm can result in 20 to 30% more photosynthesis than blue or cyan photons between 400 and 540 nm (Figure 3)[3], [4]. When light quality is analyzed based on the YPF curve, HPS lamps are equal to or better than the best LED fixtures because they have a high photon output near 600 nm and a low output of blue, cyan, and green light [5].

So when they actually "value" the spectrum according to photosynthetic activity (chart of crop plants in first link) hps mostly comes out ahead...

http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0099010

So the most important part of a led fixture is that it´s components beat the electrically efficiency of hps /put out more PAR photons per energy input. Thats why I like white Cobs.

 

[lilm00re14]

It seems like you guys have all neglected the importance of the UV spectrum as well.

http://www.mrnice.nl/forum/6-breede...cy-cannabinoid-content-cannabis-sativa-l.html

 

[lilm00re14]

From experience with my California Lightworks Solar Storm 440s\880 , i have done runs with the UVB bulbs on and off at various times. Ive noticed introducing the UVB in a vegetative state that the plants produce more oils and smell alot stronger then without. They also pull a very rich shade of green and you can see what looks like small hairs growing on the leaves. In bloom with the UVB on the plants produce resin very early which id assume is similar to how human skin tans under the uv rays of the sun .