Re: Light levels

> From: didi at wwnet_com (Didi Soichin)
>  | From: Elizabeth Worobel <eworobe at cc_UManitoba.CA>
>  | Aquatic plants saturate their photosynthetic rates at between 300 and 
>  | 1000 umol per m2 per second of Photosynthetically Active Radiation (PAR). 
>  | Anything below 100 umol/m2/s PAR should be considered low light.
> I used in the beginning 2X20W PPUT on a 29 gallon tank. That makes for
> 2760 lumens/.2323 m2=11900 lux. Amano, referring to CO2, states that
> one good indication if the plants are photosynthesizing is to observe
> them 1-2 hrs after CO2 addition. Interpolating this to "lights on"
> you would think that you are saturating the photosynthetic rates if
> the plants are bubbling 1-2 hrs after turning the lights on. Well,
> I've achieved this with the above mentioned 2X20W PPUT, which
> coincidentally would be in total agreement with the Dennerle
> recommendations. It's still hard to believe that 2 bulbs or 1.37W/G 
> is enough. 

Slight confusion here. The oxygen pearling which you observe is
saturation of the oxygen dissolved in the tank. This is not the same
as the MAXIMUM rate of photosynthesis which Dr dave is referring to
as the saturation of photosynthesis. I suspect that we only approach
this with nearly direct sunlight or perhaps with relatively strong
MH lighting. By the way, this is not necessarily optimal since it
may cause excessive growth and fast growing plants will out compete
slow growers for light and nutrients. It is great for duck-weed
propagation though! ;-)