[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: Light intensity

> Date: Thu, 13 Jul 2000 14:46:31 -0700
> From: Steve Lacy <slacy at tivo_com>
> Shouldn't we be talking about the amount of light that strikes the
> bottom of tank per area per day?  

IMHO, we should be talking about proper spectrum (for photosynthesis AND for 
viewing) and how much light intensity (Lux) each plant requires and for how 
long. We have been talking about the first but have been dancing around the 
second and haven't mentioned much about the third. 

Different plants require different levels of light (high light, low light, etc). 
Where the plants are in your tank in relation to other plants, especially tall 
ones that block light, can have a more dramatic effect than more bulbs or better 
reflectors or whatever.  

I have seen very few references to the amount of light a plant needs - Allgayer 
and Teton have a table in their out-of-print book that gives ranges of Lux for 
various species. 

If you are *really* serious about proper lighting, you would get a lux meter 
(about $100) and stick the probe in your tank and see how much intensity each 
plant is receiving. And be able to properly convert the measured Lux to 
photosynthetically active radiation (PAR) [I think that's what PAR stands for] 
using correction curves (Lux meters are tuned to response of the human eye  
which tends to be biased towards green light). And, based on The Table (perhaps 
starting with Allgayer and Teton and added to by APD people), rearrange     
your aquascape or modify your lights or pick different plants. 

Wouldn't it be cool to be able to say "Didiplis diandra requires between 1500 
and 2000 Lux to grow properly" rather than "Didiplis diandra needs 2.7 w/g [with 
all the assumptions about tank size, bulb quality, reflector shape and 
everything else which means nothing to most people]"? 

Now, if Tom Barr, who seems to have at least one of every plant known to the 
hobby and then some, had a lux meter (or borrowed mine) and took readings in the 
dozens of tanks he owns or maintains, maybe we could create such a table. 

George Booth in Ft. Collins, Colorado (booth at frii_com)