# if actinic light is blue and plants absorb blue(and red)..shouldnt actinic work?



## DtEW

I think it's because blue light makes the freshwater plant/aquascape look like crap, or at least unnatural. And it's not just about growing plants, but also about creating a good-looking aquascape.

Reef tanks use actinics because blue light is the most highly penetrative of all wavelengths, which may be the primary light that actually gets to the depth of a reef in a natural setting. Aside from the creation of a natural look (for that environment), I think various marine invertebrates are actually attuned to the blue light as biological signals.


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## nicks7.1985

i see...so they will grow?..just it will look kinda weird being blue


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## DarkCobra

Compare a reef light which has lots of actinic blue to a LED grow light, which works with terrestrial and freshwater plants:










It's the opposite - lots of red, very little blue. Why?

DtEW was correct when he said blue is more penetrative. In saltwater ocean depths, photosynthetic organisms are made to use and expect primarily blue light, because that's what they get.

Terrestrial/freshwater plants are closer to the light. They expect more red and less blue. Put such a plant under a blue-heavy light and it'll still grow. But it "knows" that more blue and less red is a sign it's being shadowed by other plants, and takes it as a cue to grow upwards, where there's better lighting. The plants put their energy into growing stems instead of leaves, and getting tall instead of full and lush.

Sometimes it's about what we want, not just what the plants want.


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## J.farrand

I'm with you, other people told me different that actinic will do nothing for plants but like you said plants absorb blue and red spectrum. So I don't see why it would just be for marine tanks.


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## Hoppy

Plants use the whole spectrum from near infra red to near ultraviolet. They reflect more of the green and yellow parts of the spectrum than they do of the blue and red parts, but most of the light is still useful to the plants. I see no reason why actinic bulbs, or bulbs sold as actinic bulbs, would fail to help the plants to grow. But, the tank would look terrible to me - I have seen a few like that and I hate that look. If you like it, then go ahead and use the actinic bulb, but report back here after several months about what the plant and algae growth are like. That is how we learn new stuff.


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## deleted_user_7

Those lights are used to grow the photosynthetic algae called zooxanthellae that live in the tissue of the host coral. They need the actinic light to replicate the lighting conditions under the sea water where they live naturally, which can be much deeper and filter out a lot of other light in some areas of the reef, whereas plants tend to live in comparatively shallow water. 

Actinic light wouldn't be good for growing plants, but would be great for use at night time as moon lighting! Even using one actinic light amongst several other daylight lamps would make things look strange as far as freshwater aesthetics go... If you've ever seen an actinic light in person they look extremely dark and remind me of the blue color of neon lights. Only good as a moonlight for freshwater.

Say you have four bulbs to choose from over your tank... UsIng three daylight lamps and one actinic would look strange with all that blue and wouldn't be what you're used to seeing and the benefit of the actinic light would be negligible compared to if you used four daylight color lamps. Of you want a once crisp whore without a slight tinge of blue, use 10,000 K.

I think plants recognise blue wavelengths and move towards them via phototropism and use that as a cue to elongate their internodal length to reach better light, so using actinic light Kay trick the plant into growing stems that are longer rather than bushier growth.


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## essabee

Actinic light has a spectrum from green to ultra-violet and different colour bands (wave-lengths) varies within this range depending upon the particular luminary used. The part of the spectrum from green to near UV will help plant's photosynthetic activity. 

Then plants do not use light solely for photosynthesis - it uses light to regulate is growth pattern too and for that it uses thew red part of the spectrum. That would be missing from your actinic light - and plants will show it by over-elongation. There are also other plant metabolic activities which are also governed by the non-actinic part of the spectrum.

Looking at the economy of actinic light use - you are converting the electricity you are consuming to produce an unnecessary part of the spectrum - UV - thats a waste you could avoid to your advantage.

As for the beauty of the end result - that is your business - so no comments.


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## HypnoticAquatic

i havent seen the cause of plants growing leggy because of blue spectrum. that should be from not enough light as blue will make it grow/mass and red will make it reproduce/flower. if u have a solid red that isnt suffcient than it will get leggy. here is a chart to help u with the spectrum an u can decide from there.


200 - 280 nm UVC ultraviolet range which is extremely harmful to plants because it is highly toxic. 
280 - 315 nm Includes harmful UVB ultraviolet light which causes plants colors to fade. 
315 - 380 nm Range of UVA ultraviolet light which is neither harmful nor beneficial to plant growth. 
380 - 400 nm Start of visible light spectrum. Process of chlorophyll absorption begins. UV protected plastics ideally block out any light below this range. 
400 - 520 nm This range includes violet, blue, and green bands. Peak absorption by chlorophyll occurs, and a strong influence on photosynthesis. (promotes vegetative growth) 
520 - 610 nm This range includes the green, yellow, and orange bands and has less absorption by pigments. 
610 - 720 nm This is the red band. Large amount of absorption by chlorophyll occurs, and most significant influence on photosynthesis. (promotes flowering and budding) 
720 - 1000 nm There is little absorption by chlorophyll here. Flowering and germination is influenced. At the high end of the band is infrared, which is heat. 
1000+ nm Totally infrared range. All energy absorbed at this point is converted to heat.


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## nicks7.1985

thanks for all the answers. i can see that just from this post the answers are varied...i think what dark cobra and hoppy said makes a lot of sense. personally i dont really like the blue look either. i think im leaning towards 3 daylight and 1 roseate. or 1 roseate, 1 actinic and 2 daylight..that may look strange though..ill try out diff combinations. this is my first tank so ill put up pics when i get everything set up and i will keep posting over the next few months pics to track the plant growth so we can see what really happens.


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## Sharkfood

If you're mixing all sorts of different spectrum bulbs, the end result wil probably look like something in the middle. Either way, your plants aren't going to die because they don't like the color of the light. If you have enough light, the plants will grow. Color temperature doesn't really tell you much about the composition of the wavelengths generated by the bulb. That being said, a bulb intended to be "actinic" looks a little strange in a FW tank IMO, but beauty is in the eye of the beholder.


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## redfishsc

I'll take a different perspective. 

I'm running a brand new setup 10g under both white LED's and royal blue LEDs ("actinic", in a sense). 


While I cannot comment on the growth of the plants, since I've only had plants in this tank for two days, i can comment on the overall look. I think the blue "punch" afforded by the RIGHT bulb is nice (Ie, a "blue" bulb instead of a "violet" bulb-- they both get called "actinic"---- you want the "blue" bulb--- much more photosynthetically active spectrum, 460nm). 


Now some comparison shots. Forgive the scuzz growing on the herb pots:icon_roll and keep in mind this tank has been running for only a week-- the setup is NOT complete yet .

White-only (13 cool white Cree XPG). Nice, but kinda washed out. Neutral white would have been a better choice I think.










Cool white XPG along with Royal Blue XRE (13 of each)










Just for giggles, Royal Blues only. This is kinda uncomfortable to look at.


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## ibebian

HypnoticAquatic said:


> i havent seen the cause of plants growing leggy because of blue spectrum. that should be from not enough light as blue will make it grow/mass and red will make it reproduce/flower. if u have a solid red that isnt suffcient than it will get leggy. here is a chart to help u with the spectrum an u can decide from there.
> 
> 
> 200 - 280 nm UVC ultraviolet range which is extremely harmful to plants because it is highly toxic.
> 280 - 315 nm Includes harmful UVB ultraviolet light which causes plants colors to fade.
> 315 - 380 nm Range of UVA ultraviolet light which is neither harmful nor beneficial to plant growth.
> 380 - 400 nm Start of visible light spectrum. Process of chlorophyll absorption begins. UV protected plastics ideally block out any light below this range.
> 400 - 520 nm This range includes violet, blue, and green bands. Peak absorption by chlorophyll occurs, and a strong influence on photosynthesis. (promotes vegetative growth)
> 520 - 610 nm This range includes the green, yellow, and orange bands and has less absorption by pigments.
> 610 - 720 nm This is the red band. Large amount of absorption by chlorophyll occurs, and most significant influence on photosynthesis. (promotes flowering and budding)
> 720 - 1000 nm There is little absorption by chlorophyll here. Flowering and germination is influenced. At the high end of the band is infrared, which is heat.
> 1000+ nm Totally infrared range. All energy absorbed at this point is converted to heat.


OoO, old but informative thread despite being short. I came across this because I was curious if our LEDs are giving off UV, effectively baking us in the sun in our own homes, which would be a terrible thing. But from what I gather, it's highly unlikely that LED brands, particularly for aquarium use, would bother including UV because it has no functional use (by plants). Is that everyone else's understanding as well?

Thanks for the great read!

[UPDATE] just realized the lowest spectrum is actually harmful to plants, so I think I answered my own question =P

The descriptions accompanying each temp range in @HypnoticAquatic's post; are the effects fairly well known that it's a good reference, or are there varying perspectives on that?


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## HypnoticAquatic

ibebian said:


> OoO, old but informative thread despite being short. I came across this because I was curious if our LEDs are giving off UV, effectively baking us in the sun in our own homes, which would be a terrible thing. But from what I gather, it's highly unlikely that LED brands, particularly for aquarium use, would bother including UV because it has no functional use (by plants). Is that everyone else's understanding as well?
> 
> Thanks for the great read!
> 
> [UPDATE] just realized the lowest spectrum is actually harmful to plants, so I think I answered my own question =P
> 
> The descriptions accompanying each temp range in @HypnoticAquatic's post; are the effects fairly well known that it's a good reference, or are there varying perspectives on that?


i wouldnt say that uv light has no functional use for plants at all. its actually quite the opposite, same goes with ir. they both trigger certain funtions. for what we would be using it for its not really nessisary though and would just increase the cost of the light. if this was for crops this would be different. 

for what we would be using its best to just get a light that is pleasant to look at imo 4500-7500k then just make sure it can produce enough par for the plants and your set up. making sure your light is putting out the correct ammount of par is WAY WAY more important than the color spectrum, granted you wouldnt be using a pure uv or ir light.


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## ibebian

HypnoticAquatic said:


> i wouldnt say that uv light has no functional use for plants at all. its actually quite the opposite, same goes with ir. they both trigger certain funtions. for what we would be using it for its not really nessisary though and would just increase the cost of the light. if this was for crops this would be different.
> 
> 
> 
> for what we would be using its best to just get a light that is pleasant to look at imo 4500-7500k then just make sure it can produce enough par for the plants and your set up. making sure your light is putting out the correct ammount of par is WAY WAY more important than the color spectrum, granted you wouldnt be using a pure uv or ir light.




Hm that all makes sense, thanks!

Is there a way to reliably figure out if a lighting fixture outputs any UV spectrum? I was originally concerned I'm constantly bathing myself and family in UV which would not be a comforting realization..


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