i found this. it says that blue light is nedded,but idk. i only know what i read with freshwater. i guess this is just another learning experince. miami dont take offence to any of this . it is a good post thogh.this post also says nothing about a actinic bulb.i wish i could find out the k rating on a actinic03blue bulb.

http://www.aquaticplantcentral.com/foru ... hesis.html

Here is an interesting response from the thread at plantgeeks. It looks like the actinic is needed to grow a certain kind of algae at the depth most coral are found. The coral then use this algae to stay alive. It is a very good answer for the marine side of things, but doesn't answer the FW question. Anyway, here it is.

Promotes welfare of invertibrates For a marine aquarium to realistically represent reef life, it is essential to provide the best conditions for corals and invertebrates to thrive. Most important in this is the survival of zooxanthellae, a specific form of algae, which symbiotically assists the invertebrates to feed and remove waste matter. In nature, the sun provides over 100,000 luxlux 'lumen per sq. metre'. At depths of typically 5 to 10 metres, where many of the corals and invertebrates are found, the visible light to be seen, is basically only in the blue wavebands, thus the familiar blue appearance. All the other wavelengths, particularly reds have been absorbed and filtered out by the salt water. This remaining blue light is the light which invertebrates have evolved to utilise for zooxanthellae symbiosis. The Arcadia Marine Blue Actinic lamp range has been created to provide the specific spectrum '400 - 480nm' necessary to achieve the blue chlorophyll absorption for zooxanthellae symbiosis to develop. This concentration of light energy in the so called actinic range peaking at 420nm, is essential for the survival and good health of fish, corals and invertebrates in marine aquariums. Another important element of the Arcadia Marine Blue Actinic lamp is the UV output present, which creates a very pleasant fluorescent effect on corals, invertebrates and exotic marine fish. When used at night with no other lamps, the effect is of a dark moonlit night with the vivid colours of the corals and invertebrates fluorescing brilliantly. When used in conjunction with the Arcadia Marine White lamp range, the high levels of light output create a most realistic marine reef environment. This combination gives the most natural and pleasant appearance and highlights the fluorescence and bright colours of the fish, corals and invertebrates, along with the correct spectrum output at the required wavelengths to achieve the reproduction of the symbiotic algae, zooxanthellae.

Is it for glass tanks? i have to be careful with my acrylic tank as the lights i have right now are close to my tank top and heated it already, bending the cover on top :(

(thanks about the pic)

SwPimp, that was a very good article you gave a link to. In that article, I found the following statement that seems to support that actinics are not good for plant growth and cause algae:

Strong blue light will cause plant growth to be more compact and bushy and will also tend to promote algae growth. So remember to balance 2/3 red to 1/3 blue light emissions.

I think his main point was that they need a combo of red and blue light, but that only blue light (i.e. actinic bulbs) were not good. Let me know if you find this interpretation incorrect. Thanks for the good discussion.

the irony of this great actinic discussion: freshwaterpleco started it