actinic good for plants?

[nvision]

hi all. i've tried doing a search, but have found no relevant results.

basically, i was so thrilled about the recent compact flourescents that i went and bought another unit for my 10g, a coralife 28w fixture. it includes a 50/50 (10,000k/actinic 03) bulb, and as i test the unit right now i'm seeing a very nice, soothing, marine-blue glow in the tank.

while the color is attractive, and with the general consensus that 6500k is best for plants, has anyone actually grew freshwater plants with actinic? i've heard that blue spectrum generally makes plant grow "bushier", and not as tall compared with white light. i'm thinking about trying it out (basically don't want to fork out more cash for an extra bulb, for now). heck, i've even come from a halogen light setup for years. doesn't hurt to try actinic while i'm at it, eh?

though it would be nice to hear of first-hand experiences from others, however. thanks in advance.

[hatton3]

I use an actinic for a moonlight effect for 30 minutes after I shut the main lights off. For my main lights, I use a 6,500K and 10,000K bulbs because I like a crisp white color. All 6,500K bulbs look too green to me. All 10,000K too blue. I'm just very picky about my lights.

[slipknottin]

the most beneficial spectrum for plants is from 5000-6500K.

I see no reason to waste electricity providing light in other spectrums that wont do any good.

[Fishiebusiness]

I've always wondered how plants react to actinic light. Chlorophyll has a blue peak and a red peak for aborbance. The actinic should target the blue peak exclusively and rather well, and not necessarily be less effective than a full spectrum 5000K. Plants have cholorophyll similar/identical to that of the dinoflagellates in corals (which the lights were designed for), although plants are probably better at using red since red does not penetrate ocean water well.

Has anyone done any controlled (not anecdotal) experiments on plants and their responses to actinic light? I'd really be interested.

[slipknottin]

Plants dont use blue light anywhere near as effictively as algae.

All plants are largely terrestrial in nature and are adapted to using the white spectrum (largely yellow, red, and some blue)

Algae are aquatic and are adapted to using blue first, and white light second.

[Fishiebusiness]

So using actinic lighting for a planted tank will promote a massive bloom of algae?

[slipknottin]

With enough nutrients, possibly.

[Slappy*McFish]

I agree, plants really prefer the red end of the spectrum.

[nvision]

thanks for the responses.

i think a plant has reacted to the lighting--wasn't good. i've ran the bulb for a day just to test it, and apparently my baby tears, which has been growing submersed (very pretty) on top of a high rock above the water surface, has drooped down tonight. this may be considered its initial reaction to the actinic lighting, but i couldn't rule out the light as ineffective because i also notice a few new stems that are beginning to grow out, albeit tiny. maybe the plant is just beginning to adjust? i'll let the light run for a few more days and see what happens. i've also read somewhere that plants do use the blue spectrum, but i'm not an expert to verify this. just have to wait and see i guess.

as for algae, i haven't noticed any difference in the tank yet. but having read that actinic promotes algae growth is really disturbing to me.

[GulfCstAquarian]

A plants photosynthetic action spectrum shows that relevant intensities of blue and red are about equal, although plants can use a broader range of low wavelength (blue) light than red.

http://www.aquabotanic.com/images/light_fig9.jpg

The key is balance. If you are supplying a great deal of excess in any part of the action spectrum, then algae will be happy to oblige and utlize that light. Algae is a very opportunistic and adaptive organism. They will use whatever light that plants aren't using (as in the presence of a low-CO2 environemtn and high light).

So if your bulb has strong output in the red and green areas of the spectrum, and weak in the blue, a supplemental actinic bulb could definitely help. You're better off finding a bulb that is designed to match the Photosynthetic Action Spectrum (like the Sylvania Gro-Lux) and not try to create that balance on your own.

[Gumby7]

I think this supports the opinion that you want a bulb with a very high CRI also.

[nvision]

ok you guys have convinced me. i have no time to play god with mix-n-match coloring. i'm getting a new bulb. :p

thanks everyone.

[125gJoe]

I'm glad you decided on a new light. It's late to post this, but I had a 50/50 Compact Flourescent and it made my aquarium look "washed out"... The tank seemed to have 'lost' rich coloration. I've heard some really like the look, but it's not for me. 50/50 lights do work well in Saltwater tanks. I have seen this. :)

[GulfCstAquarian]

Originally posted by Gumby7
I think this supports the opinion that you want a bulb with a very high CRI also.

Logic would seem to dictate so, but this is not the case at all. Quite the opposite, actually. A high CRI means that the human eye (which is sensitive to spectra on the photopic curve) sees things as they should be in the daylight noonday sun. Plants "see" with the photosynthetic action spectrum so a high CRI does not necessarily indicate a good plant bulb. If you look at these tabulated results:
Bulb specifications (http://www.aquabotanic.com/lightcompare.htm#S-5)
You'll see that high CRI bulbs such as the Philips TL950 5000K fluorescent very high CRI (98) F32T8/TL950 bulb had a very low PUR (photosynthetic useable radiation).

Basically even though to our eye it might appear brighter, than say, the Sylvania Gro-Lux, the useful output for plants is nearly one third that of the Gro-Lux!

[RTR]

Don't confuse the issue still more by confusing CRI - which is how true colors appear under a given spectrum compared to natural sunlight, with perceived brightness - which should be lumens. These are measuring quite different things, one is color rendition, the other brightness.

[GulfCstAquarian]

That is precisely how I defined CRI: As a measure that indicates that the human eye sees things as they should be under ideal sunlit conditions.

Lumens, on the other hand, provides us very little information when choosing a plant bulb. Lumens are an indication of percieved luminosity, or intensity, based on the photopic curve. The photopic curve is a weighted balance of what our eyes see, as humans.

It just so happens that the photopic curve that lux is based on is just about the opposite of the photosynthetic curve that plants are most sensitive to. Taking a look at that table, many high lumens bulbs had very low useful output in the photosynthetic spectrum. Similarly, many seemingly low intensity bulbs, such as the Gro-Lux with only 1200 lumens, had some of the most intense PUR output.

There are indeed many indicators of bulbs which provide strong output for plant growth, but most of these are misconceptions. I had been under the misconception that lumens was the most important specification to consider. Now I can see that this myth is misleading.