Wait, what's PAR?

[gradolabs]

Yeah and companies test this themselves and have settled on only basic and elementary ratios of PAR without making them adjustable to your specific needs. We have a veg bloom switch, but no real way of, say adding an additional 300 umol/m2/sec of 445.5nm blue to the lower bud sites, which could potentially affect veg and bloom.

 

[gradolabs]

Anyway I missed the point. Eek knows what PAR is now.

 

[SCARHOLE]

Measurement of par is alot better then using the old ft candles.
But even with an appogee quantum / par sensors there is error.

A quantum sensor/meter is designed to measure the total number of photons between 400 nm and 700 nm, the photosynthetically active radiation (PAR) range. The error associated with a quantum meter (or sensor) measurement of light from a source that has a different spectrum than the source used to calibrate the meter is called spectral error. Spectral error arises because no quantum meters perfectly match the defined quantum response, meaning they do not respond to all wavelengths of light equally between 400 nm and 700 nm. Apogee quantum meters are sensitive to wavelengths between approximately 370 nm and 665 nm, with a relatively flat response between 450 nm and 650 nm due to the blue pigment used in the diffuser (Figure 1). However, they are not equally sensitive to the wavelengths within the photosynthetically active range (Figure 1). In order to determine spectral error, the spectral responses of the quantum meter, calibration light source, and light source to be measured are required, along with some spectra-dependent calculations (for details, see Federer and Tanner, 1966; Ross and Sulev, 2000).

 

[SCARHOLE]

Spectum is amazing!
Evidently my induction flouro will always have a huge green spike (546nm) due to the element mercury in the bulbs.
Flouro will show as alot more par than than most lights due to this.
But the green is useless for par?

Amazingly no one makes a par meter that only uses red an blue spectrum which are used for photosynthesis. (Chmoraphil A&B)

In the 1850s By burning elements with an alcohol burner and documenting the spectrum.
Dr Bunson Somehow during a eclipse noticed the suns light was similar to the spectonomy of iron.
He used spectonomy to discover the make up of the sun.

Evidently the smaller the lines the better for DIY spectra scope.
DVD or blue ray will give more resolution than a cd.
http://sci-toys.com/scitoys/scitoys/light/cd_spectroscope/spectroscope.html

 

[gradolabs]

Spectum is amazing!
Evidently my induction flouro will always have a huge green spike (546nm) due to the element mercury in the bulbs.
Flouro will show as alot more par than than most lights due to this.
But the green is useless for par?

Amazingly no one makes a par meter that only uses red an blue spectrum which are used for photosynthesis. (Chmoraphil A&B)

In the 1850s By burning elements with an alcohol burner and documenting the spectrum.
Dr Bunson Somehow during a eclipse noticed the suns light was similar to the spectonomy of iron.
He used spectonomy to discover the make up of the sun.

Evidently the smaller the lines the better for DIY spectra scope.
DVD or blue ray will give more resolution than a cd.
http://sci-toys.com/scitoys/scitoys/light/cd_spectroscope/spectroscope.html

Max rep scarhole. You've discovered PAR. I mentioned spectral resolution in my DIY spectrometer thread. Check my sig.

 

[gradolabs]

p.s. green light is great for secondary photosynthetic pigments like carontenoids. You're alright with some green, but blue then red should dominate your spectral output.

 

[don]

p.s. green light is great for secondary photosynthetic pigments like carontenoids. You're alright with some green, but blue then red should dominate your spectral output.

interesting point ive mentioned this before and people thought i dropped from mars

its amazing a plant takes advantage of spectrum it reflects it still hurts my head

 

[SCARHOLE]

I do like the Par meter for a comparison aginst other light.
When comparing my Riant light to other induction lights it would be great.
But comparing flouro with a green spike to LED with none it would be like comparing apples to oranges.

There is a company that sells spectrum specific Testers.
422-499: http://www.solarmeter.com/model94.html
585-741: http://www.solarmeter.com/model96.html

For 250+ ea
But not one that does par from just red an blue.

 

[SCARHOLE]

Some info from a ninja...

We're on a complex topic, lighting and it's measurement, that does not warrant one or two sentence responses. But I'm going to try and keep it as simple as possible for anyone who is new to this.

Any band pass type light meter is simply reading a net photon energy level.

A quantum meter is typically calibrated for sunlight and is not corrected for human vision sensitivity. It measures whatever net light energy is sensed and converts it to the calibrated numerical value between 400-700nm. It has no idea where it is landing in that range. I can actually take a PAR reading of a monochromatic green emission at a peak of 555nm and still read a high PAR value. A quantum meter does not utilize an algorithm that would avoid this region (if this is what Kite meant I take exception and if not forgive me as this is what I interpreted your statement to mean) and weight the PAR measurement more towards the red or blue bandwidths. A quantum meter will measure the blue spectrum's in higher PAR energy values than red spectrum's as the blue regions pack 1.5x the energy as the red regions. This relationship is defined in Planck's Constant as a quantum of action in quantum mechanics whereby, for example, a 400nm photon has 1.5X the energy of a 600nm photon. The quantum or PAR meter will read this value as such. It's just measuring the photon energy at the sensor.

A photopic light meter is corrected for human vision sensitivity (photopically corrected) and gives measurements in lux or footcandle readings and will have been calibrated to a certain kelvin value. These values are based on the human vision luminosity function whereby the highest photopic value is 555nm and the scotopic value is 505nm. This chart represents the peak photopic and scotopic values and the various points on the curve where human visual perception decreases.



If anything a value that does not exist today for plant lighting should be created that represents a something in a Par/Lumen value whereby the PAR/Lumen (I made this term up) value would take into account the weight of energy at a given point on the plant sensitivity curve. But since this value doesn't exist (akin to lumens but more in line with a composite lumen:CRI value) all you can do is look to the spectral distribution charts to see relative intensities that the lamp emits to determine if you're catching the wavelengths you're looking for. If you're going through all this and still considering purchasing lights or lamps from a manufacturer that refuses to publish their spectral distribution graphs because they claim their spectrum's are proprietary than I have a really good deal on a bridge for you. What these manufacturers are essentially telling you is to buy our product based on just our claims and not the essential data you should expect that is as a minimum necessary to make an informed decision of your own.

At the end of the day you still have to determine what these values represent to you as the end user. For example the lumen is quantity and the CRI is quality. Which is more important as the balance between these two is ultimately up to you to decide. In plant lighting striking this balance between energy and spectrum is of even of greater importance since it will spell the difference somewhere between crop success or failure.

Even when presented properly it's easy to get confused as this is a complex topic. If you take nothing else from all of this just remember; A PAR measurement will be better than a photopic value since these values are expressly meant to apply to human visual regions. But just a PAR value, as measured in how many uMole are striking the sensor at a given time, should not be used to determine if the light being emitted from a given light source has adequate broad spectrum blue - red to successfully take a garden to harvest. Therefore I use my quantum meter to determine if there is enough energy hitting the plants where I want the light and I use a historical reference from my previous grows to determine if the light being emitted is of proper bandwidth. This enables me to repeat grows successfully from veg through flower with a minimum amount of stress to either me or my garden. Lights/Lamps that regularly accomplish this and are energy efficient, stable spectrum, low heat and long life are likely going to find a spot in my garden.

 

[gradolabs]

You've got a smart ninja on your hands.