What happens to Spectrum when we dim our lights?

Prawn Connery

Prawn Connery

Well-Known Member
So how else to explain? Remember, the light bounces around as it leaves the source, so the meter is picking up direct light, as well as that which has bounced off any walls, reflectors and even the plants themselves, meaning some of the light has traveled a greater distance. Grow rooms also tend to have higher ambient humidity, meaning the light is traveling through water vapour and being scattered and diffused. Different spectra are also being absorbed by the plants and other media, with the remainder being reflected back into the light meter. So that leaves three explanations:

Rayleigh scattering.

Spectral absorption - the plants and surrounding reflective media are absorbing more of the blue spectrum, leaving more green/yellow/red to hit the light meter.

A combination of the above.

The only other factor I can think of is refraction from the LED lens which concentrates the spectra closer to the source, meaning the further you move away from that source, the more susceptible the meter is to refractive angle error.

But that's just spectralation . . . er, speculation :bigjoint:
 
nfhiggs

nfhiggs

Well-Known Member
Prawn Connery said:
So how else to explain? Remember, the light bounces around as it leaves the source, so the meter is picking up direct light, as well as that which has bounced off any walls, reflectors and even the plants themselves, meaning some of the light has traveled a greater distance. Grow rooms also tend to have higher ambient humidity, meaning the light is traveling through water vapour and being scattered and diffused. Different spectra are also being absorbed by the plants and other media, with the remainder being reflected back into the light meter. So that leaves three explanations:

Rayleigh scattering.

Spectral absorption - the plants and surrounding reflective media are absorbing more of the blue spectrum, leaving more green/yellow/red to hit the light meter.

A combination of the above.

The only other factor I can think of is refraction from the LED lens which concentrates the spectra closer to the source, meaning the further you move away from that source, the more susceptible the meter is to refractive angle error.

But that's just spectralation . . . er, speculation :bigjoint:
Click to expand...
First off, I question the original claim of a shift to begin with. If Rayleigh scattering had a significant effect over such a short distance, you would be able to see a color shift just moving a white paper to the other side of the room.
 
Rocket Soul

Rocket Soul

Well-Known Member
Prawn Connery said:
So how else to explain? Remember, the light bounces around as it leaves the source, so the meter is picking up direct light, as well as that which has bounced off any walls, reflectors and even the plants themselves, meaning some of the light has traveled a greater distance. Grow rooms also tend to have higher ambient humidity, meaning the light is traveling through water vapour and being scattered and diffused. Different spectra are also being absorbed by the plants and other media, with the remainder being reflected back into the light meter. So that leaves three explanations:

Rayleigh scattering.

Spectral absorption - the plants and surrounding reflective media are absorbing more of the blue spectrum, leaving more green/yellow/red to hit the light meter.

A combination of the above.

The only other factor I can think of is refraction from the LED lens which concentrates the spectra closer to the source, meaning the further you move away from that source, the more susceptible the meter is to refractive angle error.

But that's just spectralation . . . er, speculation :bigjoint:
Click to expand...
Regarding spectrum changing due to plant absortion: could be but not sure. @Malocan actually has the data of this on his fancy lightmeter thread: he measured spectrum under 1, 2 and 3 leafs. Results were that mainly red (680 nm i think), some blue, was diminished as you increase foilage cover. Spectrum under 3 leafs was heavy in green and far red. Not sure how the spectrum would measure up in X000K but looked less red. One of the coolest factoids/experiments on this forum, miss people doing experiments like that.
 
Rocket Soul

Rocket Soul

Well-Known Member
nfhiggs said:
First off, I question the original claim of a shift to begin with. If Rayleigh scattering had a significant effect over such a short distance, you would be able to see a color shift just moving a white paper to the other side of the room.
Click to expand...
I also question original statement slightly, with the follow up question: is spectrum the same over a cobs footprint or is it possible that theres a blue hotspot in the spectrum right underneath it? That could make it easier to get a very blue reading at closer distance.
 
Prawn Connery

Prawn Connery

Well-Known Member
nfhiggs said:
First off, I question the original claim of a shift to begin with. If Rayleigh scattering had a significant effect over such a short distance, you would be able to see a color shift just moving a white paper to the other side of the room.
Click to expand...
Maybe it does change colour :wink:

How sensitive is the human eye? What about quasi-periodic changes in refractive indices due to the thermal properties of the air the closer you get to the source (LED)?

But I'm just humouring you now, because I don't really know the veracity of the original observation myself . . . though if there was a change in lux reading, I'm more inclined to lean towards it picking up reflective light as well as the original source at greater distance. And that's easy to prove: you just have to compare the colour of a wall to the original light source.
 
CobKits

CobKits

Well-Known Member
Rocket Soul said:
I also question original statement slightly, with the follow up question: is spectrum the same over a cobs footprint or is it possible that theres a blue hotspot in the spectrum right underneath it?
Click to expand...
if they werent uniform in spectrum over illuminated area youd surely see it in a mfr spec. remember they are concerned with slight chromaticity differences at a level above and beyond what we even think about. they want their architectural lighting to be as uniform as possible
 
A

amyg88

Well-Known Member
Abiqua said:
Personally I could give a fuck, I have "been lifting" since 2013, while you CONSTANTLY fucking bitch about irrelevant concepts in a pissing match with LED. That is the only reason you have some reason to come out me, when I could care fucking less about your presence, now do I?

Know how I you tell, you weren't tagged or being responded to.

So then.....
Click to expand...
*couldn't* care less. Not "could".
 
nfhiggs

nfhiggs

Well-Known Member
Prawn Connery said:
^ Difference between English and American grammar. You say tomato . . .
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No, not really. Its not about grammar - its the meaning of the words. "I could care less" implies *some* level of caring about the subject, while "I couldn't care less" implies no level are caring at all. The way one would use the non-contraction form of the expression would be to say "As if I could care less" or "like I could care less" which both imply a complete inability to care about a subject.
 
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