Will too much light cause darkening of sps ??

[dzhuo]

still does not show the colour spectrum and wavelength of these units which is proven essential in coral growth and colouration.

Well, the study focus on PAR so it doesn't include the spectrum. One of the biggest reason why people chose to use LED is the wide support of spectrums since you can easily control the white and blue balance individually. When it comes to LED, spectrum is usually not the problem.

according to the chap who did the CIE Chromaticity Meter test for my brother PAR is not an accurate measure for LED lighting as it can not pick up some wavelengths or something or other and it is emitting possibly 20-30% higher value than showed on the meter.

I am not sure about the CIE chromaticity meter but one of the most popular PAR meter (Apogee) under estimates (not higher but lower) most LED fixture:

"Apogee quantum sensors underweight blue light, and as a result, photon flux measurements for blue LEDs will be too low. Also, the quantum sensors overweight red light up to a wavelength of approximately 650 nm, above which they do not measure, and as a result, photon flux measurement for red LEDs will either be too high (if the LED output is all below 650 nm) or too low (if a non-negligible fraction of the LED output is above 650 nm). Our quantum sensors will likely provide a reasonable measurement for white LEDs because they are broadband, and because the sensors are calibrated under CWF lamps. However, because of the diversity of LED lighting systems the precise errors have not been quantified. The current spectral response of our quantum sensor can be viewed on our website (http://www.apogeeinstruments.com/qua...lresponse.html). We are currently working on better filtering in order to achieve a sharp cutoff at both the 400 and 700 nm wavelengths, but this improvement is still a few months away.

That being said, Apogee quantum sensors can be used to measure the relative output of an LED or bank of LEDs, in order to track variability in output with time or temperature for example. However, quantum sensors should not be used to characterize the absolute output of LEDs (except for the possibility of white LEDs), to compare one LED to another, or to determine photon flux for plant growth for example."

Sanjay's test is done using a LI-192SA with a LICOR 1000 data logger although I have no idea how that compare to your friend's device.

 

[ryanrid]

When it comes to LED, spectrum is usually not the problem.

disagree, especially with the older units (even a current "state of the art" vertex), due to the lack of red and violet spectrum as shown in results listed above, which now seem to be getting addressed.

I am not sure about the CIE chromaticity meter

these do not measure PAR but but light spectrum, where you can see the lack of red and violet spectrums

PAR meter (Apogee) under estimates (not higher but lower) most LED fixture:

agree 100%. We used an Apogee meter for the PAR testing results listed above. We did 2 different tests one for PAR and one for spectrum which IMO is much more accurate than a PAR test alone, as there is more to it than PAR readings alone.

CIE chromaticity meter = spectrum measurement
Apogee meter = PAR reading (not sure of the brand used but as i own it can easily check)

 

[dzhuo]

disagree, especially with the older units (even a current "state of the art" vertex), due to the lack of red and violet spectrum as shown in results listed above, which now seem to be getting addressed.

I am kind of surprise this is the case because red is in fact another spectrum which favor photosynthesis:

Feature Article: Lighting the Reef Aquarium - Spectrum or Intensity?

This study is done using a Mini-PAM meter which measures the flow of electrons or ETR within the coral tissue. I am guessing the popularity of blue has to do with the fact that most chromoproteins will fluorescent under this spectrum. Anyhow, the Radion fixture will add red and a few other options to the LED market.

Apogee meter = PAR reading (not sure of the brand used but as i own it can easily check)

I will be interested since I only know of one PAR meter comparison study: Product Review: A Comparison of Two Quantum Meters - Li-Cor v. Apogee. The much more expensive Li-Cor performs pretty similar to the less expensive Apogee. If you have access to more equipement, I think it will great if you can do a comparison (although you should properly start a new thread).