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Re: lumen ratings, watts/gallon

>Date: Tue, 10 Mar 1998 13:06:53 -0500 (EST)
>From: "Roger S. Miller" <rgrmill at rt66_com>
>Subject: Re: lumen ratings, watts/gallon

Here are some more of those complicating factors...

>Erik Olsen pointed out in a later letter in this same digest that lux and
>lumen are measures adjusted to match the perception of the human eye (I
>think they're called "photometric" measures) - and they're strongly
>weighted to green light.  PAR measures the total intensity of light over a
>range of wavelengths (I think its called a "radiometric" measure) from red
>light through violet light.
>Significance?  I noticed that the lumen output claimed on some 40 watt
>Sylvania Grolux lights were very low compared to the output claimed for
>other 40 watt flourescents.  I can't remember exactly what the values
>were, so I won't repeat them, but I think the Grolux output was less than
>1/3 the output of a GE daylight tube.
>My plants, of course don't respond as if that is true, and it only takes a
>quick look at the spectrum to figure out why. Grolux tubes provide very
>little green light, so their lumen (human perception) output is low.  They
>provide a lot of red and blue light, so their PAR (plant-perceived light
>intensity) is actually fairly high.

But... Amano claims that green light is most beneficial to aquatic plants,
and he uses only tubes with strong output in the green band!  And who
wouldn't envy his results.  So maybe the PAR formula should be redesigned.

>Most flourescent lights work within a fairly small range of lumens/watt.
>So if you can describe a light intensity in lumens per gallon, then you
>can also describe it in watts per gallon.

Most 40W shop lights are rated at around 2000 (initial) lumens.  While the
high efficiency 40W bulbs are around 3500 lumens (Philips Advantage X: 3700
lumens, Ultra TriLux: 3350 lumens).  That's quite a spread.

So the watts/gallon rule remains a rule of thumb.  I think you can use a
lower ratio if you use higher-efficiency bulbs or if your tank is large and
shallow, and vice versa.  And until there is a definitive result on which
wavelengths are best for aquatic plants, I'd stick with a full spectrum
bulb with strong output in all three red, green and blue regions.


                     Hoa G. Nguyen  
SSC San Diego D371             Email: nguyenh at spawar_navy.mil 
San Diego, CA 92152-7383   http://www.spawar.navy.mil/robots/                
  Aquarium: http://www.geocities.com/Heartland/Hills/2637/