a good read for anyone wanting LED lights or making them

[crowndroyal]

I recently just came across an article that I though was interesting. I thought it was interesting because in most of the threads I have seen people keep talking about PAR. while that is important it is not nearly as important as the PUR. which will be discussed in this article.

http://aap.atrixnet.com/?p=338

[Hoppy]

PUR vs. PAR? We barely know the actual requirements that various plants have for light, whether measured in PAR, lux, or PUR. For most plants we only know a range of light intensities that are adequate for those plants. For plants that are desired for their brilliant colors, we know roughly how much light it takes to grow them and we know that it takes even more light, in general, to get the good colors we want.

We have only a rough idea how much light a specific light fixture will give us, at some distance from the light. For many light fixtures we can only guess at how much light we can get from them.

We know for sure that any light we use will give a lot more intensity up near the waterline than down at the substrate, so almost all of the plants we use will be growing in a range of intensities, higher near the top of the plant and lower near the bottom of the plant.

Given all of those unknowns, and barely knowns, it doesn't make any sense to me to even consider PUR. If we had readily available PUR meters, that might be the better way to determine "exactly" how much light we are using, but we don't. Most of us don't even have access to a PAR meter.

I think we should set PUR aside and perhaps reconsider it in about 5-10 years.

[crowndroyal]

I think in the article they are just merely saying that not all LED lights are created equal


and that when building and buying led lights you should check the manufacture box or specifications on the PUR

[discgo]

Originally Posted by Hoppy

I think we should set PUR aside and perhaps reconsider it in about 5-10 years.

I'm not trying to be rude but why? If info is available to us than shouldn't we try to use it for our benefit?

[Hoppy]

Originally Posted by discgo

I'm not trying to be rude but why? If info is available to us than shouldn't we try to use it for our benefit?

You aren't rude to ask. I think, unless you have a PAR meter, it is hard enough to try to get close to a good PAR for your tank and the type of plants and growth you want. We don't even have very specific information about what "good" PAR means, especially since the PAR experienced by the plants depends on where in the tank the plant is, what part of the plant you are concerned with - the shoots at the substrate vs. the tops of the plants, for example, and how much shading you have in the tank. Just getting that in the right ballpark takes a lot of experimenting.

Measuring PUR isn't something we can easily do - I have never seen a PUR meter. So, at best, we are guessing on PUR, based on spectral data provided by the light manufacturer. This is an aspect of planted tank keeping that might be very interesting to some people, so of course they should do what they find interesting. But, for an average planted tank person, with average experience, it just seems to me to be an added confusion factor. If you can't even be sure how much PAR you are using, concerning yourself with PUR doesn't seem to me to be a benefit.

[xmas_one]

Hoppy, isn't PUR also different for different plants? All plants dont utilize the spectrum the same way. I think I remember Tom talking about this at some point. Unless you had all of the same plant in a tank, shooting for a given PUR would be useless.