Re: Inefficiency of Blue Light

> From: "K & A, P.A." <kapa at netrunner_net>
> Reply-To: kapa at netrunner_net
> To: Aquatic-Plants at ActWin_com
> Subject: Re: Inefficiency of Blue Light
> In response to Diana Walstad's recent query regarding blue light:
> Diana,
> I use one actinic bulb in combination with several full spectrum bulbs
> in some of my tanks.  Ususally, because I feel that I don't have enough
> light over the foreground and don't want to spend the money on metal
> halide or the like.
> It has been my experience that the actinic blue puts more light (amount
> or lux) than regular full spectrums on the actual leaves of the
> foreground plants.  The reasoning being that the blue reaches farther
> through water.

No, it doesn't reach further through water with an appreciable humic acid 
content.  420 nm light is attenuated rapidly by yellow water.

Actinic lamps are good PAR sources, but the phosphor is weak, and decays 
probably >30% per month when driven at VHO levels, this is according to 
recent data from Dana Riddle.

>  I think you are right in that aquatic plants may not use light in the
> blue spectrum as efficiently, but the fact that you are getting greater
> lux on the plant, I believe, compensates for this.  As you know, there
> have been studies (Philips) that conclude that almost any light will
> grow plants if sufficiently supplied.

That is true.

I don't know a great deal about what freshwater plants need, but I do 
know a lot about how light propagates through water filled with humic acids.

Would the planted tank community be interested in a study on this with 
water from freshwater systems?  As an example of what I am refering to, 
please see the Summer '95 issue of Aquarium Frontiers for my quantitative 
treatement of UV/vis light absorption in water from a reef aquarium.