Low light? Really?

[Judi]

Has anyone else seen this sticky on The Planted Tank? If so, what are your thoughts?

http://www.plantedtank.net/forums/light ... 12-pc.html


I know that the old "watts per gallon" thing was never very precise to begin with. It becomes even less helpful with PC fixtures, and is totally meaningless in regards to T5HO lighting. So it does make sense that we should be looking at PAR data to determine how much light a fixture gives, instead of wpg. But I am puzzled when I look at the charts, and see that a single PC bulb over a 16 inch tank is considered "low light." I have a Coralife 65watt PC fixture on top of my 20H, and while I never thought it was really high light, I'm surprised to see it rated as low light. Especially since I was getting algae, and raising the light about an inch seemed to solve the problem. And I'm growing Rotala macrandra in that tank (is it just not as fussy as I was led to believe?), and things grow so fast I'm trimming pretty much weekly.

So, I guess I have several questions. First, is this just totally off? Or, have our notions of what is considered "low light" changed over time? Maybe my idea of "low light" is different from most people's? Or, do plants not need nearly as much light as we think, as long as they have ample nutrients and co2? Do I just not get lighting at all?

It seems that the more I learn, I realize the less I know! Maybe some of these questions will be answered in Rick's lighting talk in March.

[150EH]

I think years ago we all used too much light but it also changes from type to type so much with LED's being rated a 6 times more than T5HO which is rate twice as high as CFL, etc. I think 3 wats per gallon is fairly high light and will grow most plants in a 20H, and super high light mostly comes into play with really deep tanks at 30 to 36 inches or deeper but I have read articles at Tropica with 4 to 5 wpg being used in some tanks. You just have to play with what you have to really figure it out because from blubs to fixture and then types of lighting are all so much different that no two setups are the same. There are a ton of good articles on light wattage, spectrum, etc. but somehow I always finish by scratching my head and wondering if I now know less or more after the read. There are some good articles at Tropica about light, nutrients, & C02 you might want to poke around their site.

My tank has 4.29 wpg and is 30 inches over the substrate, 1.73 wpg of that come from a fixture with very poor reflectors and is used more like a display light but even at this level I have to add some 10K bulbs for good light to reach the substrate, so I'm kinda the same way and have been playing with this for years to understand what a single tank need and if I were to switch to T5HO I would need a couple more years.

[JLW]

I'm glad to see the part about reflectors on the bottom. I've obtained a couple of the Coralife T5 systems over the years, and it is amazing. The entire bulb is basically encased in black plastic, except the very bottom of it. You lose more than 75% of the light generated that way, simply because they decided to make it space-age, trendy and skinny. Reflectors are very, very important.

[150EH]

The fixture I have with poor light is also a Coralife, it has a great reflector but the bulbs are crammed in so tight that no reflected light can get past them.