K temperature Question

[Jag1980]

One of the most interesting post I have read on this forum.
There has to be a test on this already out there somewhere with proof of the results that we can all see instead of just arguing about it?

 

[Spewn]

WPG fails because of the relationship between tank volume and footprint, actually. You illuminate a surface, not a volume, so tank volume really doesn't matter(until you start getting into some *very* tall tanks, really, tank volume is unimportant).

Compare the footprint of a 10g tank, 1.6 square feet, to that of a 55, 4.3 square feet. That's only about *half* the footprint per tank volume as the 10g! That means you need TWICE AS MUCH LIGHT over the 55g per gallon as the 10g to achieve the same light levels. This is why you see people(like myself) not having issues with light levels at or above 5wpg in a 10g tank; 5wpg in a 10g only works out to about 2.5wpg over a 55.

What's far more important is to work out light output over your tank's footprint. This will give you a number that works accross any tank excepting the very, very tall.

As for lumens vs watts, lumens is obviously a far better measure. The wattage of the bulb includes the waste at the ballast, it includes the heat, everything. Lumens do not account for how well plants use the light; this is why comparing two bulbs of the same type(say, t-8) and saying "Well, bulb X has higher lumens so it must be better." doesn't work. However trends across bulb types are quite valid. Comparing the wattage of a highly-efficient bulb style to a very innefficient one won't get your plants lit properly, but knowing that t-8s are more efficient than incandescents will get you moving in the right direction.

Lastly, while I haven't seen plants bleach in an aquarium yet, I've absolutely seen it terrestrially. Some plants just die under extreme light(120+watts per square foot of HPS), others slowly turn white. I had a coniferous plant turn brown and crispy after only a few hours under that light, temp was maintained under 25'C

 

[jmhart]

Understandable if dealing with T12 bulbs, but then if you consider that there are "low light" plants which burn under too much light and you throw the "right " amount of wattage over them while using T5 bulbs, and calculate the lumens per inch, then you may find that you are puting a whole LOT more light on those plants than you think you are. That is where I'm getting thrown yb the "watts per gallon" rule when considering the difference in light output between T5 and T12 as an example, much less halogen, T5HO, and so on... Following the watts per gallon "rule" may ensure that you are not short of light, but it seems t me that it could lead you to put WAY more over the tank than you want for the types of plants you are growing.

http://www.plantedtank.net/articles/Light-Bulb-Comparison/29

Yes, you do have to factor in bulb type. That article shows you a comparison, and gives you a normalization factor to compare different bulb types.

One of the most interesting post I have read on this forum.
There has to be a test on this already out there somewhere with proof of the results that we can all see instead of just arguing about it?

Well, Tom has said he has performed test, and as it applies to the aquarium, bulb temperature doesn't matter. However, the quantum meter I've ordered will allow similar tests.

 

[Spewn]

Well, Tom has said he has performed test, and as it applies to the aquarium, bulb temperature doesn't matter. However, the quantum meter I've ordered will allow similar tests.

How will a light meter determine how light colour affects plant growth behavior?

 

[Spewn]

Something tells me you're thinking the issue is whether or not colour temp. has a direct effect on PAR values. It doesn't, and that has nothing to do with what I've been talking about.

 

[jmhart]

Something tells me you're thinking the issue is whether or not colour temp. has a direct effect on PAR values. It doesn't, and that has nothing to do with what I've been talking about.

I interpreted his question more as an effectiveness of particular bulbs, not of color temperature.

Additionally, as I've said, bulb temperatures according to packaging are completely worthless. They are worth about as much as claims on a bottole of Enzyte. Most manufacturers pick a temperature rating that approximates the color projected by the bulb, which in many cases doesn't reflect the actual K, in order to communicate to consumers. I think you are under the impression that for your run of the mill fluorescent bulb, the kelvin rating is 100% accurate. If this were the case, why would so many manufacturers provide a spectrum with their bulb? If you compare mulitple 10,000k bulbs, looking at their provided spectrum, why are the spectrums all so different? If they were all really 10,000k, shouldn't they provide the exact same light? Since we both understand that a Kelvin rating relates to the emission of carbon at a particular Kelvin setpoint, shouldn't the label "10,000k" be standard? Leave it to the scientist and that is the case, but once you involve the marketing department, and suddently science doesn't matter so much.

For my own purposes, the quantum meter will allow me to say "This bulb produced by this manufacture performs in this manner". For me, this will be much more informative than any watt, kelvin, or lumen rating provided on the packaging.

I still feel that all evidence to support the hypothesis that bulb temperature effects plant growth is entirely subjective. Personally, I've run all sorts of bulbs, and ultimately, the only thing I've noticed that is important is providing enough light. To be fair, I haven't used bulbs outside of the "6,700k" to "10,000k" range. However, within that range, the only difference I've noticed from any bulb is how my plants appear to me. Never have I observed a difference in aquatic plant growth due to bulb color.

 

[Squawkbert]

Right -

CRI - higher=better, is an approximation of how closely the light resembles sunlight with respect to color

K - Kelvin temp rating, well covered above, has not a lot to do with spectral output of a bulb (critical to plants) or CRI (critical to tank owners). For proof, look at the spectral outputs of several 10,000K bulbs - some are suitable for corals, useless to plants - some are the exact opposite, yout can also be 10,000K rated.

Watts - Once you're taken the relative efficiencies of different bulb types into account (T5, PC, MH, HQI etc.) (PAR helps you do this), watts are watts.

Spectrum - For plants, you've got to have some light in the correct portions of the UV spectrum - the best plant bulbs have lots of output in these wavelengths. The most popular plant bulbs probably compromise a little bit to strike a balance between having a plant friendly spectral output and a decent CRI.

 

[jmhart]

I agree with what Squawk had to say 100%. That's why it's really nice to hear recommendations from experienced folks about what, exact, bulbs they use. I don't think there's a lot of info available on the forums where people compare their experiences with bulbs of similar type(temperature, bulb type, and wattage) from different manufacturers.

Currently I'm using a 10,000k, 96w PC bulb from AHSupply, but I can't say that it's any better or worse than a 10,000k bulb from any other manufacturer.

 

[Spewn]

In order to say k rating is useless, you're going to have to demonstrate that spectral output amongst identically-rated(temperature) bulbs is wildly different. I've never seen such a demonstration, not amongst bulbs of the same type.

 

[jmhart]

In order to say k rating is useless, you're going to have to demonstrate that spectral output amongst identically-rated(temperature) bulbs is wildly different. I've never seen such a demonstration, not amongst bulbs of the same type.

I think to the hobbyist, this is likely impossible to do. The equipment required woud be entirely cost prohibitive. Tom may have done this in his research. I'll ask next time I see him.

To the hobbyist, I think the only way to achieve this is to setup identical tanks, as nearly as possible, with the only difference being the color bulbs used, and then watch the growth, keeping everything else as identical as possible. The error involved would be huge, but it might give us a decent idea. After several months, you'd have to compare the tanks under the light that each was grown with, but you would also need to switch the bulbs(only for a minute) to compare the tanks under the other tanks light, just to make sure it's not a perception issue.

Very good discussion, by the way.