How biologically important are actinics? (not a newbie question)

[maroonclown]

We add in these bulbs, but why? It is my understanding that full spectrum lighting has a better effect on coral growth than actinics do. It is also my understanding that these bulbs are more for aesthetics. So my question is; why spend our money on these bulbs? Considering how most of us run our PC tubes with one white and one actinic, it seems to me like there is a loss of the more useful spectrum in the white tubes. If we use actinic for a dawn/dusk cycle, couldn't we use a much smaller tube to save space for the white light? Please post your opinions/advice.

 

P.S., this is just to stir-up conversation/information.

[FishinAggie03]

The actinics are to supplement the blue spectrum into your tank that your corals need. With 5500k and 6500k actinics are needed. With 10000k bulbs, supplemental actinics aren't totally necessary. The reason that actinics are needed is because of the filtering effects of water. In the ocean, the blue spectrum is filtered out last, meaning that corals recieve a lot of this color. So this is why actinics are added. HTH

[apophis924]

Atinics are more for the viewing than anything else. How many corals flourence in their natural enviroment. Light is filtered out of sea water as a function of depth. Unless your tank is more than 15 foot deep there is now loss in the quality of full spectrum lighting. Now intensity will fall as the distance between the light source and the coral increases but if your tank is less than 15 feet deep there is NO loss in the quality of your light spectrum there is simply not enough water between the light sopurce and the coral to have any real effect unless your water is dirty or has a high load of DOC's. that can interfeare with light transmission and abosorbtion.

[EtOH_is_good]

I'm not an expert, but from my photography knowledge, doesn't light intensity decrease not at a linear rate but as the distance squared? This applies to air, so water clairty (diffraction) must also modify the equation. So there must be some loss of intensity even if the distance between the light source and the bottom of the tank is less than 15 feet.

 

Why else would reefers put the light loving corals on top and the lower light requiring corals on the bottom even in nano tanks?

 

Water will filter out selected wavelengths of light. My college physics was a while back, so I don't remember the equation to calculate at where certain colors will be lost. From practical experience in a swimming pool, you don't have to go down to far before things start taking on shades of blue.

[apophis924]

And if you read the post correctly i said ligt intensity will decrease as a FUNCTION of depth i never stated it was linear or not: you implied it was linear. light intensity will decrease as a function of the inverse square. double the distance and you get 1/4 the intensity. that applies to a vacum when you add a medium like water the inverse square rule still applies when passing thru a medium such as air or water photon/waves are bent defracted and absorbed and re-emitted, Your lower energy wavelengths will be abosorbed and "stoppped" (for lack of a better word) while your higher energy wavelength (blues and violets ) will penetrate a bit deeper before they also become ineffective. In salt water this begins to happen as shallow as 6 to 10 feet. I doubt there are any nano tanks let alone home reef tanks 6 to ten feet deep. The depths of the average Home reef hobbiest tank be it nano or full scale set up rarely goes beyond 4 to 5 feet in depth. The inverse square law applies to intensity as far as light color (wave length) that is not affected by distance that is affected by the properties of the substance emitting the light and by the abosorbtion/reflection/defraction and or deffusion of the meduium in which the light is passing thru.

[EtOH_is_good]

apophis924, thanks for clearing up the difference between light intensity and wavelength absorbance. This has been real helpful for my understanding of lighting my future tank.

 

I'm still a little confused about color absorbtion in salt (sea) water. Does the use of actinics suppliment the weak to low blue wavelength provided by full spectrum PC lighting (I don't know how to say this w/o using intensity)? Will blue wavelength from actinics be absorbed in nanos? If using a MH 20k, will animals on the edges/bottom of "light intesity" flourence because blue wavelength is not lost?

[rehren]

Why else would reefers put the light loving corals on top and the lower light requiring corals on the bottom even in nano tanks?

 

bottom of the tank can also be shadowed by things up top, so it's not always that distance from light is consideration, but what gets the most direct light vs. things that may only get partial light due to objects above them.

[onthefly]

If you go to SPSFrags.com, Patrick says that some of his corals will only thrive, if supplied with intense lighting PLUS actinics. More than likely, some of the symbiotic organisms utilize the lower wavelengths. I'd say 95% of Actinic is for viewing, but 5% is biologically relevant, depending on the coral!