LED lighting advice please

[Picavorus]

I've just bought a couple of white full spectrum daylight bulbs (came from the hydrophonics shop), along with a red and blue LED bulb to put into my terrarium - hopefully the neps will appreciate them.  I also have it close to a large south east facing window which allows plenty of natural light into it as well.  There are just so many different ones out there, it seems to be a minefield.  If it doesn't seem suit them, I'll have to try a different set up of bulbs.

Edited September 28, 2016 by Picavorus

[Yossu]

42 minutes ago, manders said:

Its a very complicated compromise, plants phtosynthesise the most with red and blue light, as thats what chlorophyll a and b absorbs.  Thats why the most 'efficent' way to grow plants is thought be with red/blue LED (any why pants look green as they dont use green light).  Green light is what looks brightest to humans.  So reproducing 'daylight' produces a lot of green light that plants simply dont use and therfore its not the most efficient (ie uses/wastes more electricity) .

What makes it complicated is that plants have other pigments other than chlorophyll and these absorb other wavlenghts of light to do other usefull things.  Some plants even deliberatley use this trick to survive in deep shade by utiising wavelenghths other plants just don't use.  I have one which grows really well in the deepest darkest corner of the greenhouese underneath a bench where even ferns struggle.

You wouldnt go far wrong with either warm white or daylight or a mix of both.  Ideally though you want a bulb that has more red and blue in it but inevitably they are more expensive as they are not 'mass market'. 

Thanks for the explanation. As you can see, I know little about these, but am learning fast!

I'm going to try one warm white and one cool white, and see if there is any difference. Always like an experiment!

Thanks again for all the help. At some point, I think it would be useful to summarise the info here and post it as a sticky. I'm clearly not the only one who is confused, and it would a great help to people like me to have it clearly summarised. Would you be interested in doing this? I would, but I don't know enough to be sure I'd be writing the right thing!

[manders]

BTW by coincidence i just bought an LED light for the fishtank, it's a mixture of cool white and blue LEDS, might be a good way of mixing in some blueish light on top of a terrarium.

[mobile]

1 minute ago, manders said:

BTW by coincidence i just bought an LED light for the fishtank, it's a mixture of cool white and blue LEDS, might be a good way of mixing in some blueish light on top of a terrarium.

I've got one of them too which used to be above my nano reef tank.

[mobile]

Got the full spectrum LED wired up, utilising an old halogen desklamp.

Sent from my LG-H815 using Tapatalk

[Yossu]

You say it's full spectrum, but it looks very red. Can you clarify?

[mobile]

Full PAR spectrum 380nm - 840nm. This LED is specific for plant growth. As was mentioned earlier in the thread, plants need primarily red and blue light to photosynthesise and a few auxiliary wavelengths. There is hardly any green spectrum in this LED, as that's wasted energy on plants, hence the red/purple colour you see.

[manders]

42 minutes ago, mobile said:

Full PAR spectrum 380nm - 840nm. This LED is specific for plant growth. As was mentioned earlier in the thread, plants need primarily red and blue light to photosynthesise and a few auxiliary wavelengths. There is hardly any green spectrum in this LED, as that's wasted energy on plants, hence the red/purple colour you see.

I just realised you can get a lot of led grow lights at good prices on ebay these days.  I'm tempted but the weird colours attract nosy neighbours. (Been there done that).

Also tempted to get a waterproof one for the greenhouse.

[Yossu]

1 hour ago, mobile said:

Full PAR spectrum 380nm - 840nm. This LED is specific for plant growth. As was mentioned earlier in the thread, plants need primarily red and blue light to photosynthesise and a few auxiliary wavelengths. There is hardly any green spectrum in this LED, as that's wasted energy on plants, hence the red/purple colour you see.

Ah, PAR spectrum. Didn't know what that was until just now, but it's quite different from how I interpreted full spectrum. Thanks for the clarification.

[Yossu]

30 minutes ago, manders said:

I just realised you can get a lot of led grow lights at good prices on ebay these days.  I'm tempted but the weird colours attract nosy neighbours. (Been there done that).

Also tempted to get a waterproof one for the greenhouse.

There are loads of led grow lights, but the problem is, how do you know what is any good. I started this thread because I'd seen some that looked very good and very cheap. The comments I got here suggested they were "garbage." How would you sift through the hundreds on offer to decide what's good?

I've ordered a couple of the white ones linked earlier, one warm white and one cool, but I would be interested in trying some PAR ones as well. I have about 200 sarracenia seedlings here, so I have plenty to experiment on! I would like to set up a few areas, each with different lighting, and see how the plants compare after a few months (or whatever). Would be helpful to know what you look for in a bulb.

Thanks again.

[mobile]

One thing to check It's the wavelength of the red LED. Ideally it should be 660nm to correspond with the chlorophyll absorption band but on cheaper grow lights they are often only 620-630nm.

[Yossu]

2 minutes ago, mobile said:

One thing to check It's the wavelength of the red LED. Ideally it should be 660nm to correspond with the chlorophyll absorption band but on cheaper grow lights they are often only 620-630nm.

Thanks for that. Anything else? A lot of them don't seem to go into too many specifics about the wavelength. Do I take that as an indication that they aren't so great?

[mobile]

10 hours ago, Yossu said:

Thanks for that. Anything else? A lot of them don't seem to go into too many specifics about the wavelength. Do I take that as an indication that they aren't so great?

I'd want to know the wavelengths if I was buying and I would see how they match up to chlorophyll a and b absorption bands. For anything other than seedlings, I'd look for lamps that use high power LED, not clusters of low power chips.

[manders]

Another problem with chinese made LED growlights is its become normal practice to misquote the power rating.  For example a 30W light might have 30 1W Leds or 10 3W Leds but thats misleading.  The LEDs are often only running at about 50-70% of maximum power ie somewhere between 15 and 20W.

For normal bulbs thats less of a problem, the quoted power is more often correct, but not allways.

 

[mobile]

3 minutes ago, manders said:

Another problem with chinese made LED growlights is its become normal practice to misquote the power rating.  For example a 30W light might have 30 1W Leds or 10 3W Leds but thats misleading.  The LEDs are often only running at about 50-70% of maximum power ie somewhere between 15 and 20W.

For normal bulbs thats less of a problem, the quoted power is more often correct, but not allways.

 

I've seen this with a UFO style growlight plugged into a power meter.

[manders]

And another point. PAR 38 etc actually refers to the physical size of the bulb and has nothing to do with PAR as in the type of light produced.

[Peabody]

The thought I have got on LEDs is that some plant leaves have colouration and are not "green". So presumably the colouration will have a filtering effect on whatever spectrum of light is shone on it.

[mobile]

@Peabody the colouration of the leaves is the reflected colour, so not used by the plant.

[manders]

12 hours ago, Peabody said:

The thought I have got on LEDs is that some plant leaves have colouration and are not "green". So presumably the colouration will have a filtering effect on whatever spectrum of light is shone on it.

This is a complicated question.  Plants use different pigments for a wide variety of reasons, as camoflage, as sunscreen, sometimes because they grow in dark places and utilise light of different wavelengths. Calatheas are a good example of the latter, they will grow where few other plants will, by reflecting red light back into the leaf from the underside they get a second chance of photosynthesizing the light which ordinarily would have passed through the leaf.

 

 

Edited October 2, 2016 by manders

[manders]

Yet another thing to remember, photosythesis still occurs even with green light, its just at a lower rate.  

Some of the claims for b/r LED efficiency are based on some very dodgy assumptions and calculations.  Yes they are more efficient, but not as efficient as manufacturers claim (salesmen are the same everywhere).  Much of the efficiency gain compared to flourescents is simply by going to the best efficiency LEDs.

My suspicion is there isn't a huge efficiency gain going from white LED to red/blue LED and the grow room doesnt look like a bordello with white LED.

 

 

 

Edited October 2, 2016 by manders

[mobile]

55 minutes ago, manders said:

Yet another thing to remember, photosythesis still occurs even with green light, its just at a lower rate.  

Some of the claims for b/r LED efficiency are based on some very dodgy assumptions and calculations.  Yes they are more efficient, but not as efficient as manufacturers claim (salesmen are the same everywhere).  Much of the efficiency gain compared to flourescents is simply by going to the best efficiency LEDs.

My suspicion is there isn't a huge efficiency gain going from white LED to red/blue LED and the grow room doesnt look like a bordello with white LED.

There is an article here explaining antenna pigments, which absorb different wavelengths and are used by photosynthesis: http://plantphys.info/plant_physiology/light.shtml

This Emerson action spectrum graph, from the link above, demonstrates efficiency very well I believe:

[manders]

Good article, and now heres the catch.

To get maximum efficiency, you need at least three wavelengths, blue and two reds.  The tricky part is try finding an LED growlight that has both 680nm and 700nm red wavelengths.  If you dont you are not getting the real benefits.

All the cheap leds only have have 630nm wavelengths. So you can either pay a lot for a decent quality led growlight with at least 3or4 wavelengths of the right type, or get a white LED which is far cheaper and in reality probably only a bit less efficient.

At a guess the most efficient LED growlight may only be 30% at the most, more efficient than a warm white LED, particulary as warm white leds don't produce overly large quantities of green light anyhow.

if anyone finds a cheap led with blue, 680 and 700nm let me know i might want to try it.

 

Another twist to all this is most of the lab experiments are done on a relatively short time scale.  If the only light you provide is red/blue and you dont provide light for example for the beta-carotenes, then over longer periods of time it can destroy the chloroplasts.  The beta carotenes help to mop up dangerous chemicals produced during chlorophyll photosynthesis.  Im pretty sure thats what happened to some of my plants back in the early days of led growing.

 

 

[mobile]

@manders, this is why I bought the full spectrum PAR LED. The seller I bought it off did not have the spectral distribution graph posted but I found this one for a similar LED which suggests that the far red wavelengths you mentioned are present. Unfortunately I do not have anything to confirm this though:

 

[mobile]

The one that @Peabody linked to earlier in the thread does have the spectral distribution graph: https://www.amazon.co.uk/dp/B01DBZK3V6?psc=1

[manders]

Thanks Mobile, i found a few sellers offerring the bridgelux full spectrum chips.  They do look really interesting, i guess i would have to dissasemble an led light fitting and solder these guys in, which im not sure i can i can bothered with all the hassle.

If they start selling lights allready made it might be more interesting, also i still prefer to avoid the bordello effect.

Anyways, theyre cheap enough i might order a few and try modify one of my PAR 38 bulbs.