Lighting Kelvin & Algae Question

Hi friends, I have a little question need your good advise & recommendations.

I faced this issue of 6,500k, 10,000k & even 20,000k colour temperature issue for the FL light tubes. If I'm not wrong all light up the tank equally right? Doesn't mean 20,000k will shine brighter than 6,500k and so on right? The brightness is thus derived from the wattage of the tubes right, please correct me if I'm wrong.

And is it true the higher the color temperature, it encourages algae growth so eg. 20,000k tubes will encourage more algae growth than the 10,000k tubes provided same number of tubes being used and equal amount of lighting hours etc.

In this case, is the 10,000k tube or 20,000k tube better for creating the mid-day sunlight? Considering using 2 tubes both 54w each for a 5x2.5x2.5 tank.

6500k FL light will look brighter than 20kk, but it's very yellowish. 20kk lamps are very dim and blue. If u have VHO light which is much higher wattage, it's brighter and provides more light intensity (higher Lux measurement). A 24" NO tube is 20W while a 24" VHO tube is 75W. Low wattage FL light can only keep zoos, mushrooms, soft corals and some LPS corals.

Some manufacturers name their FL daylight tube as 50/50 which is equivalent to a 10kk tube. 6500k light promotes algae growth, not 20kk light. Noon sunlight has a full spectrum temperature ranging from 5800k to 6500k. If u use only 20kk light, u can see that coraline algae growth is luxuriant but little green/brown algae.

If u intend to keep corals, u must try to meet their photosynthetic requirements. I don't think u shld use FL light for a 2.5ft height tank, u can go for 250W MH (10kk) supplement with two actinic tubes. MH provides the proper PAR which is the light radiation available for use in photosynthesis.

I concur with Maculosus. If you are going into reef.. FL is definitely not enough to sustain the corals. 10,000k tube will actually encourage algae growth more than 20,000k.

[BarraCuda™]

Just to add on

How bright actually depends on our eye's sensitivity. Our eyes cannot see light wavelengths at the 2 extreme ends, infra red, ultraviolet.

Blue lights will appear dimmer because they emit light at wavelength that is near UV. 6500K should be the brightest because most of their light spectrum is within the range of the human eye.

Can anyone advise if the luxmens is proportional to the kelvin? Any relationship between them?

luxmens measure how "bright" is the light
kelvin measure the colour of the light...
the colour
red -> orange(e.g. 6.5k) -> white e.g (10k) -> blue (eg. 20k)

From my own understanding, lumens measures "visible lights". More towards the yellow to white lights. Thus many serious reefers use PAR instead since PAR measures the full photosynthesis spectrum.

As such, based on these terms, lower kelvin will give a lower lumens values but it does not means that the light is not "bright" enough for photosynthesis. Instead it may even be brighter.

Another question - since lower kelvin make algae grow faster, does it means that SPS will become brown faster?

Originally Posted by jc85

Another question - since lower kelvin make algae grow faster, does it means that SPS will become brown faster?

Firstly, good water quality is important for SPS corals and will also impair algae growth. I have read elsewhere that certain wavelengths are responsible for promoting the vivid coloration in SPS corals. Blue light stimulate the fluorescent pigments.

Yap. I agreed gd water quality is utmost important.

I made an assumption that water quality is of no concern. So if the SPS is expose to lower kelvin for long period, they will turn brown?

As for the fluorescent pigment, there are thoughts that its due to UV exposure. That's why many feel that MH can bring out stronger pigment.