Why CO2 once over 3 watts/gallon?

[happychem]

and I've been a tastelessly good little boy all, um, month to get on the "Nice" list

 

[Jay]

And you will never go back to diy!
Do whatever it takes to stay good for another 30 days!
End BBA in your lifetime!!

Jay

 

[spinjector]

As for the wpg threshold, that's a little more hand-wavey, and very subjective....So treat watts per gallon more as a very vague ballpark figure and work from there.

THANK YOU!!! :bowing:

There are so many many many factors that make WPG a blurry figure (pun intended). Tank depth, plant coverage, bulb reflector, type of bulbs, age of bulbs, temperature of bulbs, efficiency of power supply, and even the A/C mains voltage it's all plugged into - it can vary from 110v to 125v. And this is all assuming fluorescent bulbs, PC, or MH - with the new LED light sources requiring something like 2% the power of conventional light sources for the same brightness, trying to specify WPG would be like trying to explain how thick the orange rind is on your apples.

Why doesn't someone hatch a new standard of measurement like Millicandellas per Square Inch, or Lumens per Square Foot, or something like that...??? But of course with appropriate admonitions of diffusion due to tank depth and plant denisty...

 

[RTR]

Lumens are measures of perceived brightness as seen by the human eye. That unfortunately has little to do with the wavelength plants use. Watts, so long as the bulbs are listed as triphosphor or broad spectrum, is likely to be the best available rating.

 

[H3D]

Lumens are measures of perceived brightness as seen by the human eye. That unfortunately has little to do with the wavelength plants use. Watts, so long as the bulbs are listed as triphosphor or broad spectrum, is likely to be the best available rating.

Lumens are not a measure of brightness or perceived brightness. It is a measure of the total amount of light given off by a light source, within the visible light spectrum (380-770nm), weighted to the sensitivity of the human eye. That being said the human eye can see almost all the wavelengths of light that plants need to grow. The real problem is that we cannot see the light within these wavelengths when it is at certain intensities. This problem can easily be overcome by finding the Kelvin rating of the bulb.

 

[happychem]

Lumens are not a measure of brightness or perceived brightness. It is a measure of the total amount of light given off by a light source, within the visible light spectrum (380-770nm), weighted to the sensitivity of the human eye.

That's the same thing as RTR posted, just different words.

The problem is that our eyes are not identically sensitive to all wavelengths. It's got nothing to do with not being able to perceive various wavelengths at a given intensity. The point is that we detect light in the green region of the spectrum much more strongly than light in the red or blue region. Plants, as a rule, don't use green light - hence green leaves and evolutionarily our increased sensitivity for the colour of most autotrophs.

The kelvin rating of the bulb is only an approximation of the colour given off. It refers to the peak in the spectrum of a blackbody radiator that would best approximate the light given off by the bulb. Fluo bulbs are not blackbody radiators, they're fluorecent radiators (hence the name ), so while the kelvin rating isn't a bad way of telling what general wavelength distribution a bulb produces, it's not a spectal chart and it has nothing to do with light intensity.

 

[H3D]

What I said is is not the same as what RTR said.

"The problem is that our eyes are not identically sensitive to all wavelengths. It's got nothing to do with not being able to perceive various wavelengths at a given intensity. The point is that we detect light in the green region of the spectrum much more strongly than light in the red or blue region."

The reason our eyes are not as sensitive to all wavelengths is because our eyes cannot perceive the photon flux (intensity) of the light equally, and actually we are most sensitive to yellow-green light because we perceive red light as being the brightest. The reason our eyes detect more green light is because our eyes are more sensitive to green light at much higher intensities than red or blue light, therefore we see more green light in the visible spectrum.

"The kelvin rating of the bulb is only an approximation of the colour given off. It refers to the peak in the spectrum of a blackbody radiator that would best approximate the light given off by the bulb. Fluo bulbs are not blackbody radiators, they're fluorecent radiators (hence the name ), so while the kelvin rating isn't a bad way of telling what general wavelength distribution a bulb produces, it's not a spectal chart and it has nothing to do with light intensity."

The Kelvin rating refers to the temperature, of the theoretical blackbody. The theoretical blackbody radiator does not have a peak in wavelength spectrum (the theory holds that the color light given off is equally intense), thus differentiating it from a fluorescent bulb which has peaks in intensity. While a Kelvin measurement of a fluorescent bulb is not accurate in the "technical" sense of the word, it does allow us to approximate the color and intensity of the light given off.

 

[happychem]

Took me a while to figure this one out...

The reason our eyes are not as sensitive to all wavelengths is because our eyes cannot perceive the photon flux (intensity) of the light equally

The word "because" refers to a causal antecedent. Your antecedent is only a repetition of your precedent. In other words this sentence doesn't say anything other than "Our eyes are not equally sensitive to all wavelengths". The term "photon flux", btw, should never be used in conjunction with "wavelength", one is from photon theory, the other wave theory. Regardless, the fact that our eyes do not perceive photon fluxes with varying energy levels equally efficiently is the definition of not being equally sensitive to all wavelengths, not a reason for it.

and actually we are most sensitive to yellow-green light because we perceive red light as being the brightest.

This is contradictory.
Sensitivity to a particular wavelength, or the efficiency of the photocell in our eyes, refers to - in this case - the relative brightness we would report is all light at all wavelengths were being emitted at equal intensity. Therefore, if all wavelengths are emitted equally, and we perceive red as the brightest, then we are most sensitive to red, not yellow-green. The fact is, we are more sensitive to green because if all were emitted equally, we would report that one to be the brightest.

The reason our eyes detect more green light is because our eyes are more sensitive to green light at much higher intensities than red or blue light, therefore we see more green light in the visible spectrum.

This is either nonsensical or poorly written. Relative sensitivity refers to how strongly we detect light of different wavelengths being emitted at the same intensity. If one wavelength is being emitted at a higher intensity, and we report it as brighter, it's meaningless.

The Kelvin rating refers to the temperature, of the theoretical blackbody. The theoretical blackbody radiator does not have a peak in wavelength spectrum (the theory holds that the color light given off is equally intense), thus differentiating it from a fluorescent bulb which has peaks in intensity. While a Kelvin measurement of a fluorescent bulb is not accurate in the "technical" sense of the word, it does allow us to approximate the color and intensity of the light given off.

Yes, a theoretical blackbody radiator does have a peak in its spectrum. Although perhaps the word "acme" or "wavelength of maximum intensity" would have been less confusing. The spectrum of a blackbody radiator (with wavelenght on the independent axis and intensity on the dependent) is shaped like a reverse hyperbola, the wavelength at which the highest intensity is observed (which I refered to previously as the "peak") is determined by the temperature of the radiator. I'll crack open the old Quantum text when I get home and post the visible colours based on absolute temperature. Suffice it to say for now that the visible colour shifts towards the blue with increasing temperature.

Nonetheless, it is still completely unrelated to the intensity of light produced by the bulb.

 

[plantbrain]

Oh heck, this sounds like the APD

Buy a PAR light meter and be done with it.
We grow weeds, not eyeballs here.

The watt/gal rule has never failed me except in very small tank systems and it's not because of the watt/gal issue, it's because I have only a few choices that will add light over a small area.

I have a PAR meter and have measured everything all over and nothing was unexpected except the PAR levels where higher on my test tanks that I thought(450 vs 300-350um/m^2/sec). This is for a pair of new 5000K/8800K PC 55w bulbs at a 4" distance and around 100 at 16" depth. Old 4 year bulbs: 400 and 85. So anyone wants to offer me their 1-2 year old bulbs, I've still never had anyone offer me a free bulb to date.

So the plant will get different light PAR on the tops vs the lower leaves.
Plants also adapt very well over time to whatever light is provided.

Regards,
Tom Barr

www.BarrReport.com









Regards,
Tom Barr

 

[H3D]

"The word "because" refers to a causal antecedent. Your antecedent is only a repetition of your precedent. In other words this sentence doesn't say anything other than "Our eyes are not equally sensitive to all wavelengths". The term "photon flux", btw, should never be used in conjunction with "wavelength", one is from photon theory, the other wave theory. Regardless, the fact that our eyes do not perceive photon fluxes with varying energy levels equally efficiently is the definition of not being equally sensitive to all wavelengths, not a reason for it."

The modern conception of light is that it is a form of radiation made up two characteristics photons and waves. There is no repetition in my previous statement. Inability to see certain color light at high intensity is the cause of our eye's sensitivity to different wavelengths.

"This is contradictory.Sensitivity to a particular wavelength, or the efficiency of the photocell in our eyes, refers to - in this case - the relative brightness we would report is all light at all wavelengths were being emitted at equal intensity. Therefore, if all wavelengths are emitted equally, and we perceive red as the brightest, then we are most sensitive to red, not yellow-green. The fact is, we are more sensitive to green because if all were emitted equally, we would report that one to be the brightest."

If all light in the spectrum were emitted equally at a low intensity, yellow green would be the brightest. If all light in a spectrum were emitted equally at a high intensity, green would be the brightest. As the intensity of red light increases our visibility of it decreases. If we were to look at each light color independently, at an equal low intensity, red would appear the brightest. If we were to do the same thing at high intensity we would only be able to see the green light.

"This is either nonsensical or poorly written. Relative sensitivity refers to how strongly we detect light of different wavelengths being emitted at the same intensity. If one wavelength is being emitted at a higher intensity, and we report it as brighter, it's meaningless."

Eye sensitivity depends on light intensity.

"Yes, a theoretical blackbody radiator does have a peak in its spectrum. Although perhaps the word "acme" or "wavelength of maximum intensity" would have been less confusing. The spectrum of a blackbody radiator (with wavelenght on the independent axis and intensity on the dependent) is shaped like a reverse hyperbola, the wavelength at which the highest intensity is observed (which I refered to previously as the "peak") is determined by the temperature of the radiator. I'll crack open the old Quantum text when I get home and post the visible colours based on absolute temperature. Suffice it to say for now that the visible colour shifts towards the blue with increasing temperature.
Nonetheless, it is still completely unrelated to the intensity of light produced by the bulb."

There is no peak or light of higher intensity in the theoretical blackbody. The Kelvin measure, highest temperature of the radiator, corresponds to the wavelength (or color of light) given off. Since the light in a fluorescent bulb does have peaks in intensity its Kelvin rating is said to be inaccurate. However it is still very useful to us as an approximation of the color and intensity of the light given off.