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Discussion Starter · #1 ·
So I've been using a 4x55W CF fixture on my 33L for some weeks now since it's been set up (and years ago in my previous incarnations in this hobby), and I've always used actinic bulbs in half the sockets and 10K bulbs in the other two. I used actinic based on the knowledge that the spectrum it puts out closely matches the absorption spectrum of Chlorophyll A. So I thinks "hey, that must be really good for plants".

But here I now read that it's not so good for plants, but with little explanation as to why.

Anyone have any reasons why it's not ideal?



PS: just placed an order for 6700's to replace the actinics a few minutes ago.
 

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I'm actually pretty sure you're right, in that actinics closely match chlorophyll absorption, and actually work pretty well for growing plants. I haven't heard of anyone who actually runs just actinics in a planted tank though, probably because they look terrible on them, in my opinion. Just too much blue.
 

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Discussion Starter · #3 ·
Oh, I agree they're a bad choice for a freshwater planted tank by themselves (aesthetically), but I'm just wondering about all the negativity about them being rather useless for growing plants.

All the spectrum charts for the various actinic products all show a maximum around 430, while it stays rather high through 450. Chlorophyll A and B peak at about 430 and 450, respectively. On this alone, it seems to be a rather good choice for a [green] plant's energy requirements.
 

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It's because water is blue, and so it absorbs the light from actinics.





Kidding.

Seriously, I've read that there's a range of light wavelengths that is good for aquatic plant growth that is different than what would be useful for plants grown out of water. I don't know if it's true, and I don't necessarily care due to aesthetics, but I'd love to know the answer to this too.
 

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People who have multiple identical sized tanks could do us a service by running a comparative test: set up two identical tanks, same substrate, same plants, same fish, same filtration, but one has some actinic light and the other doesn't. Both have the same light wattage and light bulb type - PC's, T5HO's, etc. After 3 months it should be obvious whether there is a significant difference with the two light spectra.

This could even be done in a single 55 gallon tank, with a black plastic divider in the middle, and one half lit with actinic+ 10,000K light, and the other with two 10,000K lights, both 65 watt PC lights, or 24 watt T5HO lights.
 

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I am not sure this would have much effect but I do know that there is about 1/3 the par value at 18 inches with a true actinic compared to a 6.5 or 10 k bulb but only about a 1/3 drop in par value with a blue bulb caompared to a 6.5 or 10 k bulb, oh and a true actinic 430nm is closer to purple while blue actinic 460nm is blue
 

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I am not sure this would have much effect but I do know that there is about 1/3 the par value at 18 inches with a true actinic compared to a 6.5 or 10 k bulb but only about a 1/3 drop in par value with a blue bulb caompared to a 6.5 or 10 k bulb, oh and a true actinic 430nm is closer to purple while blue actinic 460nm is blue
I overlooked the obvious in my suggested experiment: It would be very helpful if someone with access to a PAR meter, and with an actinic light fixture, to measure the PAR at various distances from the bulb. If that were done first with an actinic bulb, then with a 10,000K or 6700K bulb, the comparison should be very interesting. Really, that should answer the question about whether an actinic bulb is effective for growing plants. I have no idea whether the "actinic" bulbs that are usually supplied with light fixtures are true actinic or blue actinic bulbs.
 

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It's my understanding that atinics will grow plants just fine - it's just butt ugly.

a par test would be interesting- can't remember if that had been done or not where I've read the above info.

cheers-k
Check out the link above and it might help. It also depends if they are true actinics or blue actinics IMO
 

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I checked the link but it doesn't include 6700k and colormax for comparison- b/c a reefer would have no use for them. plus i'm not familiar with all the manufacturer names- but I'm guessing all the ones that say something about day or sun are 10,000k. I guess it's clear not all actinics are created equal and presumably aqua blue or actinic plus will do better than true actinic but it doesn't help us compare other planted bulbs. I'm too lazy to look it up but there's a really good old thread on here about bulb comparisons if you search for it Alpinst

cheers-k
 

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There is enough information on that Reef Central thread to be able to say that a typical actinic will not produce as much PAR as a typical 10,000K or 6700K bulb. How significant this would be, given that so many T5HO lit tanks are over lighted, is hard to say. I always come back to the fact that I just hate the appearance of actinic lighted planted tanks.
 

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I checked the link but it doesn't include 6700k and colormax for comparison- b/c a reefer would have no use for them. plus i'm not familiar with all the manufacturer names- but I'm guessing all the ones that say something about day or sun are 10,000k. I guess it's clear not all actinics are created equal and presumably aqua blue or actinic plus will do better than true actinic but it doesn't help us compare other planted bulbs. I'm too lazy to look it up but there's a really good old thread on here about bulb comparisons if you search for it Alpinst

cheers-k
Near the bottom of the list is a GE 6500k, that and the Geismann 6000k might give something to compare to.
 

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Sorry I am use to talking to reefers. I posted the kelvin ratings next to the bulbs and the ones with the ?? I am not sure on but those are my guesses.

ATI

Sun Pro 357 6k ????
Aquablue 336 12k
Blue Plus 311 14k
Actinic 137

D&D/Giesemann

Midday 325 6k
Aquablue 324 11k
Actinic Plus 264 blue actinic
Pure Actinic 157

AquaZ

Sun Pro 285 6k????
Ocean Pro 323 10k????
Blue Pro 266 blue actinic?????

Helios

Daylight 309 10k
Super Blue 225 blue actinic

Current Sun Paq

Daylight 10K 272
Blue 252

GE Daylight 340 6.5k
 
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