CRI, Photosynthesis 6/25/09
Hi Crew,
<Hello Joey>
Why is it that, "for the sake of photosynthesis in aquaria, CRI values of ninety (90) or greater are called for?" (Fenner). If a bulb has high intensity in the short red and blue spectrums, and a color temperature of
5000K+, what makes a high CRI value necessary for photosynthesis? Or do those other measures relate to/determine the CRI? I ask partly because I have gotten the impression, digging around the internet, that a high CRI usually means an unattractive, harshly white light.
<CRI (Color Rendering Index) is a quantitative measure of the ability of a light source to reproduce the colors of various objects faithfully in comparison with an ideal or natural light source, such as the sun. CRI by itself does not necessarily indicate what the color temperature of the reference light source is, and that is where Kelvin temperature comes into play.>
Thanks for the guidance,
<You're welcome. James (Salty Dog)>
Joey E

Re: CRI, Photosynthesis 6/27/09
Thanks for the response.
<You're welcome.>
Are you saying that the perfect 100 CRI bulb renders them the color that natural sunlight would, because the bulb's light illuminates them so,
<Nope.>
or that the light, through photosynthesis, causes them to become the color they would be if sunlight were photosynthesizing them? If you mean the former, as I suspect, then what role does the CRI value play in photosynthesis in the aquarium? Will my plants not grow as well with a low CRI value, or is the concern merely that they will not be rendered they way they naturally would?
<If you read my definition of CRI again, as I mentioned in the previous email, it says nothing about photosynthesis. We can have an 8 watt bulb with a CRI of 98, but it isn't going to do too much for photosynthesis in a 55 gallon tank, not enough intensity and lumens.
What we generally look at now is the Kelvin temperature and wattage of the lamp. Many moons ago, when standard fluorescents were our only choice of lamps, CRI was a factor, as it was a good indicator of the usefulness of the lamp for plant growth. Back in those years, Vita-Lite manufactured a twisted fluorescent tube that had a CRI of 91, and a Kelvin temperature of 5500K, and was widely used
by aquarists for growing plants.>
Thanks for working through this,
<You're welcome. James (Salty Dog)>
Joey E

Lighting query (again) - LED's and colour temps 4/19/09
G'day crew
<Hello Leon.>
Hope today finds you well. As always thanks for a fantastic service, and thanks in advance for whoever is on duty today for the advice...once again on my "favourite" topic: lighting.
<Today was fine, Scott V. with you tonight.>
First question is regarding colour temperatures (K), and is this: "If colour temperature is based on changes in colour when heating a black body radiator to a specific temperature, why do some bulbs (often from reputable manufacturers) which have the same colour temperature rating give off a visibly different light colour?"
<Simple, they are not accurately rated.>
A good example here is 10k tubes...just about every brand has their version. But if we take a couple of high-end 10k lamps - say an Arcadia original tropical lamp and an Aqua Medic Ocean White - we see a marked difference. The Arcadia has a slight pinkish/purple look to it, whereas the Ocean White is a very crisp, bright white. Then compare these with a more mid-range product such as Catalina PC's and you'll find that the Catalina 10k's appear slightly more yellowish.
<Agreed.>
To take this one step further I'll use another mid-range bulb, the Hagen Power Glo, as an example. It has a K rating of 18k, but has a visible pinkish colour to the light...not at all the very blue light that you would
expect from a bulb of this temperature.
<Yep.>
Is this all to do with the human eye's sensitivity to various spectra, or is it creativity from the manufacturers' marketing departments, or is there some other standard or factor that I'm simply not aware of (which I think
is probably the case)?
<No universal standard and lack of actual spectral testing.>
Second questions is regarding LED lighting...
There are a few, apparently good, products slowly becoming available in Australia. I have been doing a bit of reading about LED systems in general but a lot of the info I've been able to find (including some interesting commentary on WWM) is anywhere from 4-10 years old. The general message seems to say "promising technology, but expensive and still having some trouble with light quality and spectral range"
<My sentiment, I do feel it will replace all in the years to come.>
Given how quickly technology improves I'm just wondering what the current status of LED technology is? For example, has the spectral quality been able to live up to fluor/MH standards?
<Sort of, it all depends on what bulbs the LEDs are compared to...for my money not there yet.>
Do you know of any recent comparative studies?
<No.>
Also, can you point out some "reputable" products on the markets which I can do some further research on?
<PFO Solaris fixtures are the standard thus far.>
In Australia we tend to be flooded with products from the Chinese market, some of which are actually really good value-for-money, others which are just a complete waste of time. This link (
http://www.oceanus-light.com/lumenaqua36.html ) is one such product, though I'm not sure which category it fits into yet. The idea of a variable spectral range is very appealing, but I question the reliability of the
data as it all appears very market-orientated with a distinct lack of scientific info to back it up (e.g. spectral output graphs).
<Well, there are many DIYing these LED fixtures nowadays too.>
Thanks again
Leon (Brisbane)
<Welcome, Scott V.>