Reefs.org Forums

[Solarreef]

Who has any of these and if so, can you post your values for various positions in your tank(s). I have one but an not sure how accurate mine is, I would like to compare values with people who similiar set ups. And with other people

Thanks,
Solarreef [img]images/smiles/icon_biggrin.gif[/img]

[Solarreef]

No one has any light intensity meters, I find that hard to believe!
Bump

Solarreef

[galleon]

Solarreef, I have plots of our research system, they just haven't been put onto a computerized (ie, postable) format yet...I'll get back to you the instant I get them on a computer plot.

[KenH]

I have access to all types of light meters and have measured some of my setups on occasion, primarily to measure light drop-off over time. Most of my measurements are under 400W 10K bulbs. What kind of lighting setup do you have?

--- Ken

[Solarreef]

Hey Galleon I am looking forward to reading your data when you post it [img]images/smiles/icon_smile.gif[/img] . KenH I have 3 VHO bulbs on my 55, even though your set up is much brighter I would still like to know your levels! Do you think you could measure the levels near different corals? That would be great. I have a cheap one ~50 dollars and it reads about 3,500 foot candles or 38,000lux 5 inches below my bulbs, and about 25,000 lux where my T. Maxima and acropora are.
Looking forward to your levels

Solarreef

[dela]

sorry this is wordy..

I have a light meter for work, but have never tried it in my tank.

What I want to know is why do people use illuminance (foot candles & Lux) to describe the amount of light in an aquarium? I see it in books all the time & I scratch my head every time I see it b/c I don’t agree to use this. The reason is this.


foot candle (illuminance unit) = cd / square foot

cd (candela) = lumen / steradian


The problem is that a lumen is a watt x the human visual response curve (during the day). So a greenish light, a reddish light, and a bluish light will all give you dramatically different illuminance readings even if they are the same efficiency/wattage and producing "the same amount of light".

You won't perceive it as the same amount of light b/c that's not how your eyes are designed.

I think it's a particularly screwed up unit to use in aquariums simply b/c reefs need blue light & that's where our visual curve falls off to almost nothing. So in theory, I could have 4 VHO 20000K bulbs (or something like that) and get the same reading as one NO 3000K Home Depot T8 lamp. See the problem?

(assuming the meter corrects for color)

Does anyone know of a better lighting unit that is used? I remember reading a while ago that used an 'einstein-something'. That might be a better unit if it leaves out the human perception aspect. [img]images/smiles/icon_wink.gif[/img] [img]images/smiles/icon_wink.gif[/img]

[Solarreef]

I would like to know more about this too. I think it is a good indicator for how much light is in your tank. I know we don't see very well into the violet spectrum, a little better in the blue, but those aren't the only wavelenghts that corals use. In the Modern Coral Reef Aquarium it states: "The most common pigment chlorophyll a, shows maximum absorbtion in the range of 430 to 670", with a large ammount absorbed at 440nm and 670. So So wave lenghts of less than 500nm are not the only light waves used. There are also other light absorbing pigments. It is obviously not the most accurate, but it does a good job.

There is something called: einstein/m^2/s, where einstein =1 proton(is it a photon?) at standard h * 6.02*10^23. Which is just an amount of energy per square meter per second. A rate of energy flow. But that is just the total energy in light. Not all that energy the corals or more specificaly the algae use. There is PAR-photosynthetically available radiation, but I don't know anything about it.

All in all I believe Lux meters to be a good way of determining the ammount of energy that is usable by corals. It is not perfect, but neither are Ammonia, Nitrate, Phosphate test kits....

[galleon]

Intensity is far more important than spectrum. I'm sure you realize that the brighter something looks, the more lumens it has, and, directly, the more lux it produces (lumens/m^2). Yes, lumens rely on a visibility function of a target area of the spectrum, but, a higher lumens value always means brighter light. Period. Watts never mean the same amount of light, its not necessarily a direct relationship. And intensity is more important to the animals we're keeping than spectrum. Secondly, the other unit you brought up, uEinstein/m^2/T ("T" usually = seconds, uEinsteins are one millionth of 1 mole of photon, so yes, the human aspect is left out) is actually a measure of irradiance (the amount of light actually reaching an object), and while I believe it is a better measurement, I don't think its nearly as practical as a common lux meter. Solarreef, 6.022x10^23 particles is Avagadro's number (ie, 1 mole), 1 uEinstein, which is what I believe you mean, is 6.022x10^17 photons, if I'm wrong about your meaning, I apologize.

[ June 01, 2001: Message edited by: galleon ]

[Solarreef]

Galleon, I agree with what you have said, and when I said Einstein/m^2/s, I wanted to say E/m^2/T , where T=seconds. And yes I know 6.02*10^23 is Avogradro's number. 1 mole of Oxygen takes up a volume of 22.4 litres, has a mass of ~16 grams... I think one Einstein=1 proton (do you think proton was a typo for photon?) at certain frequency*6.02*10^23. Your are talking about micro einsteins, I was talking about Einsteins.

Yeah, I knew I was talking about irradiance, but thanks for clearing it up.

[galleon]

<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR>Originally posted by Solarreef:
<STRONG>Your are talking about micro einsteins, I was talking about Einsteins.</STRONG><HR></BLOCKQUOTE>
Ahhh....ok I gotcha...helps if you read posts carefully, don't it? [img]images/smiles/icon_wink.gif[/img]
<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote

(do you think proton was a typo for photon?)

I'm assuming so...photons are discreet amounts of light, often referred to as "packets", and they compose electromagnetic waves (and interesting enough, light can be absorbed at no less than one photon at a time), the idea was published by Einstein I believe in the very early 1900's. Protons are positively charged particles in the nuclei of atoms and composed of two U (+(2/3)) quarks and one D (-(1/3)) quark, and make up an element's atomic number. I don't think its discovery is actually credited to anyone, my guess is that sometime between Chadwick's work and Thomson's work they realized there had to be a positive particle in the nucleus.

[ June 01, 2001: Message edited by: galleon ]

[galleon]

Solarreef, I just reread your post and found your comment on photosynthetically active radiation (PAR). Generally, PAR is measured in uEinstein/cm^2/T or expressed in PPFD (Photosynthetic photon flux density), and simply refers to wavelengths between 400-700nm.

[ June 01, 2001: Message edited by: galleon ]

[galleon]

boy, just call me thread killer

[Guy]

Ok! Galleon is a thread killer, Galleon is a thread killer na na na na na na!

[galleon]

...I swear, its like a thread is getting four posts every couple minutes...I post something...and it just dies.

[RichMacys]

You know what they say about know it alls? Watts almost always mean more light. Unless your out to design a heat lamp. [img]images/smiles/icon_cool.gif[/img]

[Solarreef]

Bump, any other people?!