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Re: Aquatic Plants Digest V4 #609

"Wayne Jones" <waj at mnsi_net> wrote:

> very interested if you were to try some Philips 950 lamps mixed in with the
> 850s and if you thought there was any improvement in plant growth with them.
> I only started using them because of the super high CRI and the fact that
> Frode Ro uses them but was very suprised by an improved plant growth.

Wayne, are you using the US-available Philips TL/950, or the European 
TL'D/950 ? I believe Frode uses the 'D type, and there is a *huge* difference
in performance in between them. .

> Does anyone out there think that the concentrated spikes in an 800 series
> spectrum is in any way less desirable for plant growth than the less spiky
> spectrum found in 950 lamps or even for that matter in cool white lamps.

There is a huge difference in the spectrum between different lamps which 
otherwise bear the same /950 spec. For instance, the TL'D is a true "full 
spectrum" lamp with an even distribution of ligth along the wavelength scale. 
The PLL/950 (Philips compact fluorescent) has a peaky spectrum which is almost 
identical with a /850 tri-phosphor (again the term !) except for the relative
strength of the three main spikes. The TL/950 looks like a tri-phosphor with 
the peaks at the wrong locations, all three in the wavelength range 500-580 nm.

I've been thinking about your idea on the narrow and very brigth spikes being
in some way damaging to plants. I came up with a line of reasoning that
involves both the spectral response of particular pigments in the plant, and
the overall intensity level put out by the lamp relative to "natural"
light. The light put out by the lamp would be damaging to the plant IF the
total light integrated under the pigment's spectral curve, and weighed by the
curve, is much larger than levels found under natural conditions. It  doesn't 
really matter how narrow is the lamp's spike. What is relevant is how narrow 
it is _relative_ to the pigment's spectral response. 

AFAIK most plant pigments have very broad spectral responses with relatively
minor peaks, if any. So the very peaky light put out by the lamp would be
effectively strongly "smeared out" by the pigments' spectral responses. In
other words, the pigment cannot tell apart photons from the exact wavelength
of the spike from photons at any other wavelength under its spectral
response. Or, the pigment cannot "see" the spikes, and would respond in a
similar way to the spiky spectrum as it would to a "full spectrum" put out by 
a say, C50 lamp. What really matters is the _integrated_ ligth.

When smeared in that way, the resulting light level "seen" by the plant at 
any  particular wavelength would be extremely reduced, and probably lower 
than levels existing under natural conditions. I still need to quantify
this line of reasoning though.

Of course, this is all very speculative.

- Ivo Busko
  Baltimore, MD