kelvin, light & color temp - Page 2 - Tropical Fish Keeping - Aquarium fish care and resources
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post #11 of 41 Old 10-05-2012, 12:08 PM
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You want the light above the tank when there are plants. As someone mentioned, they will grow toward the light. I tried an experimental 10g using natural daylight from a window, and the plants grew to the back of the tank. Viewing the tank was also next to impossible.

I would caution on any type of side lighting that aside from the above issues this might bother the fish. Fish naturally expect light from the top down, and most of our fish occur in quite dimly-lit waters, so any light at the side that is bright enough for the plants is almost sure to cause problems for the fish. My window experiment was not bad for this, since the window went up and there was light coming naturally from above and behind.

Byron Hosking, BMus, MA
Vancouver, BC, Canada

The aquarist is one who must learn the ways of the biologist, the chemist, and the veterinarian. [unknown source]

Something we all need to remember: The fish you've acquired was quite happy not being owned by you, minding its own business. If you’re going to take it under your wing then you’re responsible for it. Every aspect of its life is under your control, from water quality and temperature to swimming space. [Nathan Hill in PFK]
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post #12 of 41 Old 10-05-2012, 04:59 PM
lighting and kelvin, and lumens & Par.

Kelvin is "appearent" color spectrum
Lumens are "appearent" brightness (to humans)

what appears bright to humans lots of green, some red, even less blue
what appears bright to plants, lots of blue, some red
to plants green is as good as lights being off.

Kelvin is a rating of apparent color spectrum.
looking at bulb spectrums of various T5 HO lights from 6500K, 10,000K, 460 Actinic, 420 actinic,
-6500k has a broad range high in green and blue (green so it's bright to us, blue so it's bright to the plants, and enough red to balance things out)
-10,000k, the greens are less (aside from a spike so it's still bright to humans)
-both actinic lights, focus almost exclusivly on the blues heading into violets as the spectrum approaches and enters UVA & UVB light

Florescent lights on the market all include significant spikes in the green and yellow so that it appears bright to humans, tranlation, ... takes away from spectrum light that are beneficial to plants, ... you can only put so much phosophorous coating on the lights before it blocks more light than it converts into the desired spectrum.

clorophyll benefits almost exclusivly in the blue & the red. more in the blue for growth, more in the red for flowering and blooming, ... and ever kelvin spectrum i've seen the red is shifted to a shorter wavelenths closer to the oranges than the deeper reds the plants would benefit from per watt.

if you want to see what looks bright to a plant have a look for LED lights in google images, ... it's a very purple color to us as they're cutting out the wavelenths that don't benefit plants

for water depth and color wavelenths, ... reds get cut out first, (around 10m or so), followed by yellows and greens till all that's left are blues and even these at depths of 100m below the surface are pretty much gone too. life at these depths and lower either don't have eyes, or are a sucker for the lantern fish that has the light bulb coming out of it's forhead.

for those talking about the 2feet or so doesn't matter too much to light density in the water, ... it's significant, a 1000watt HPS looses about 50% of it's light intensity every 4" in the air, i came across one site that mentioned how quickly light intensity diminishes in water but didn't think the details were important at the time, ... but consider the following:

basic sunlight, about 5500K, at the equator on a clear summer day is about 120,000 lumens, ... and the reds from this are effectivly blocked by about 30feet, that's loosing about 4000lumens of that wavelenth every foot of depth, (the math is not reliable just an estimate for the sake of coming up with numbers)

for corals this does not matter, for vegitative growth this is not a major concern, for flowering this should be at least 'food for thought'

for calculating lighting requirements the basic rule of thumb of 2wpg (watts-per-gallon) is based on T12, 3500K "soft light". i never looked at what this spectrum looks like, but i don't expect a lot of blues in it at all which are most significant for all types of plants, saltwater, freshwater, houseplants and forests alike.

how this translates into 6500K lighting for freshwater plants, or 10,000K + Actinic lighting for coral/marine tanks, i have zero idea, i could not find any sites even pretending to offer conversions.

how this translates into LED lighting, i have even less idea as for plants these lights are using different scales i could not find (did not look too hard) to compare with T5HO florescent lights, how T5HO compaires to T12, 3500K soft light, ... we're not even compairing apples to oranges anymore, might as well compair a the apple with the lantern fish. the old guestimations for "how much light is sufficient" doesn't translate into "we now have some exacting light spectrums that pinpoint the exact frequencies that benefit the clorophyll & carotoids specificaly for plant growth coming out of these super efficient LED lights. (that have no relation to Kelvin and show Lumens are for our benefit only)"
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post #13 of 41 Old 10-05-2012, 06:20 PM
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you are equating chlorophyll (a) absorption/action spectra with plant growth and development; they are not the same

you are correct that luminous flux (measured in lumens) is a measure of light as perceived by humans, this is a point I've made before, if you know this you should realize that your example of light attenuation using lumens as the units with a steady decrease per foot is not accurate, to use lumens, each wavelength would need to be considered separately

if you are correct that red light (or some red light) doesn't make it to the bottom of an aquarium, we would notice a difference in the appearance, e.g. the bottom of the tank would be shifted blue, it is not, there is consistent color rendering throughout the tank

you are also equating Kelvin with spectrum, Kelvin, first and foremost is a temperature scale where
K = degrees Celsius + 273.15, it's application invloving color has to do with incandescence and black body radiation
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post #14 of 41 Old 10-05-2012, 06:59 PM
Freshwater aquarium plants benefit from lighting with a Kelvin temperature in the range of approximately 6500 degrees. Freshwater plants prefer light with more red in the spectrum (see PAR Section).

It is noteworthy that Fluorescent and even more so incandescent lights produce a lot of yellow and green nanometer light, which research indicates is mostly wasted energy in terms of the needs or freshwater plants and SPS Corals. This is where an LED Aquarium Light, Metal Halide, or even (to a lesser degree) T2 Lights excels as there is much less wasted yellow/green light.

See the picture to the left that shows a T8 5500 daylight aquarium light that is commonly sold, this graph clearly shows the wasted green/yellow energy as well as the incorrect spike in orange rather than the correct PAR spike in red 630+ nm (click to enlarge)

It is also noteworthy that many "terrestrial plant lights" as well as many aquarium plant lights (often are lower in kelvin temperature) have more "red nanometer spikes" than higher kelvin 6500k, 10,000k & higher lamps.
The problem with these lights is that while all plants utilizing photosynthesis require the same essential ABCs of PAR (see the PAR section), the facts of light energy penetrating water requires higher kelvin (6500k +) be added to provide maximum PUR (see Useful light energy/PUR section). Aquatic Plants and corals have adapted/evolved to the natural light energy at certain depth of water and the misguided attempt to adapt these terrestrial plant lights is not going to be 100% effective as a light with more water penetrating blue & slightly lower red nm energy

Last edited by Reefing Madness; 10-05-2012 at 07:08 PM.
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post #15 of 41 Old 10-05-2012, 07:06 PM
This diagram shows the depth that light will penetrate in clear ocean water. Because red light is absorbed strongly, it has the shallowest penetration depth, and blue light has the deepest penetration depth.
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post #16 of 41 Old 10-05-2012, 07:09 PM
i thought kelvin in regards to black body radiation and it's presumed appearent light output roughly translates into, a black-body raised to X Kelvin degrees is expected to have an appearent visual light radiation that relates to the Kelvin rating we see on lights for growing and aquariums. (if i worded that right)

giving us a visual simular to this:

while what makes up the kelvin rating on our lights is more like this:

not to scale for each of them, but both seem to be 6500K lights, yet what composes their spectrums appears to be quite different

(while the first is labled as a GE 6500K, the second was just another one i found using google, so i won't vouch for it other than it's description in the post it came from)

but to the human eye the mix each gives off will appear to be simular, both 6500K
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post #17 of 41 Old 10-05-2012, 07:17 PM
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the scale of that diagram is 300 meters depth, exactly how does that relate to an aquarium two feet deep?
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post #18 of 41 Old 10-05-2012, 07:25 PM
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the spectra are different because Kelvin ratings cannot be directly applied to fluorescent sources, for these it is only an approximation, the light from the bulbs with the spectra shown above is different, but they have both been given the same K rating

the spectrum of an incandescent source does not have the spikes as do fluorescents, it is flat with a positive or negative slope depending on the temp/light emitted

Last edited by Quantum; 10-05-2012 at 07:31 PM.
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post #19 of 41 Old 10-05-2012, 07:27 PM
blue light is not penetrating beyond 300m (about 1000feet)
red on the other hand dissapears rather quickly by comparison. (in the ocean and lakes)

correct me if i'm wrong (as i'm going off memory), but i think i came across somewhere that mentioned the saltwater in the ocean allows light to penetrate farther. is it significant, probably only to a scientist and their numbers, in the real world, i don't think so

for a home aquarium, ... the absorbtion of slower red light by water in 2feet of water i don't think matters much beyond a numbers game, ... but you can find those numbers games when looking up LED lighting to find the PAR & PUR values that the companies want to use to sell you their light over the competition
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post #20 of 41 Old 10-05-2012, 07:41 PM
and incandescant lighting using the tungstan (if i remember correctly) fillament is about the biggest waste of watts/light output on the market.

tungsten is not a theoretical blackbody used for kelvin ratings. it's going to have it's own unique spectrum output as do all elements in the periodic table.

the most elementry i'm familiar with tends to suggest the light spectrum output of each metal is simular in color to it's oxide, ... light from iron is more red, copper more green

incandesant lighting is also lower on the UV spectrum as well compaired with all floresent lighting (studies have shown measurable health and cancer risks with floresent lighting - but these studies are deemed inconclusive and not accepted in N.America) something that is not a concern with household LED lighting

yes, household incandesant lights have a rather flat gradient through the spectrum, low in blue, higher in reds, and highest in infrared (hence the heat)

metal halide uses a metal fillement as well and has a remarkably different spectrum
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