Par across different lighting technology

[Sdot]

Maybe this is a silly question, but is there a difference in par from different lighting technologies? Example if i have corals under 500 par with T5, would 500 par under LED's be more/ less or equal intensity...same question for Metal halide? I ask because i read that the PUR of LED's are higher than other popular lighting methods, which is why 300-400 par under LED's is more than enough for any coral/ anemone. Is there any validity to that statement.

Thanks

 

[NeveroddoreveN]

My understanding is that PAR is how much light energy falls between 400 nm and 700 nm.

That said, chlorophyll doesn't evenly use the light spectrum, mostly red and blue. The green is largely reflected so that's what we see. Generally, the red side is better at plants and algae, and coral better utilize blue and violet. This is why violet LEDs look dim but have so much par. Also, you generally see blue reef lights and red refugium lights.

Notice the peak around 430

Action spectrum - Wikipedia

en.m.wikipedia.org

 

[Nano sapiens]

Maybe this is a silly question, but is there a difference in par from different lighting technologies? Example if i have corals under 500 par with T5, would 500 par under LED's be more/ less or equal intensity...same question for Metal halide? I ask because i read that the PUR of LED's are higher than other popular lighting methods, which is why 300-400 par under LED's is more than enough for any coral/ anemone. Is there any validity to that statement.

Thanks

PAR, 'Photosynthetic Active Radiation', is a measurement of all the visible light that we humans can see (generally accepted as all the wavelengths between 400nm and 700nm). Doesn't matter the light type, if the PAR reading is the same for multiple types...it's the same.

Of more relevance for us actually is PUR. PUR by definition is 'Photosynthetic Usable Radiation' and is made up of those wavelengths that are theoretically available for photosynthesis. LEDs typically put out more 'blue' light which the corals' algae are adapted to utilize for photosynthesis than most other light sources at the same PAR intensity level, and so there is less of the other spectra that may only weakly contribute to photosynthesis.

 

[Sdot]

PAR, 'Photosynthetic Active Radiation', is a measurement of all the visible light that we humans can see (generally accepted as all the wavelengths between 400nm and 700nm). Doesn't matter the light type, if the PAR reading is the same for multiple types...it's the same.

Of more relevance for us actually is PUR. PUR by definition is 'Photosynthetic Usable Radiation' and is made up of those wavelengths that are theoretically available for photosynthesis. LEDs typically put out more 'blue' light which the corals' algae are adapted to utilize for photosynthesis than most other light sources at the same PAR intensity level, and so there is less of the other spectra that may only weakly contribute to photosynthesis.

So then in essence.. LED is putting out more light at any given par than other lighting sources? So in theory my last statement is correct?

 

[oreo54]

So then in essence.. LED is putting out more light at any given par than other lighting sources? So in theory my last statement is correct?

Depends on the wavelength..:)
A green diode could have 100 PAR but only 30 "PUR"..

Since you need photon counts you need to consider efficiency..

PUR for white LED's would be lower than say PUR from a deep blue metal halide at the same PAR due to the drop in PUR due to the green/yellow "excess" in the LED.
It gets sort of complicated..
photons/watt so to speak.

Current quality diodes meet or exceed all other current light sources in photons/watt though cheaper diodes don't.
Above is enhanced by the better "delivery systems" of the LED's.
Lensing of the diodes could make it seem like they are more intense than measured..i.e unrecorded hot spots.
Increased PAR is the normal result. Increased PUR depends on spectrum.

Example if i have corals under 500 par with T5, would 500 par under LED's be more/ less or equal intensity

Getting back to the orig. question..It depends on your def of intensity. If just considering PAR w/ equal spectrums no. If considering PUR.. well see above.

Not sure the above is very clear but it should help.

 

[Dana Riddle]

Maybe this is a silly question, but is there a difference in par from different lighting technologies? Example if i have corals under 500 par with T5, would 500 par under LED's be more/ less or equal intensity...same question for Metal halide? I ask because i read that the PUR of LED's are higher than other popular lighting methods, which is why 300-400 par under LED's is more than enough for any coral/ anemone. Is there any validity to that statement.

Thanks

Your line of thinking is correct. As soon as I get current projects out of the way. I'll post a chart of PUR from various light sources.

 

[Nano sapiens]

So then in essence.. LED is putting out more light at any given par than other lighting sources? So in theory my last statement is correct?

As 'oreo5457' mentioned, it's a bit involved.

Simplifying, just think of PAR as the 'overall intensity' (regardless of the color of the wavelengths) and PUR as the type of wavelengths needed for photosynthesis. Give the coral more of the wavelengths it needs for photosynthesis and you can give the coral less overall light intensity.

 

[Sdot]

Your line of thinking is correct. As soon as I get current projects out of the way. I'll post a chart of PUR from various light sources.

Thank you sir!!!

 

[dave001]

OK so way back when we measured lumens or lux....how much light falls on a hives surface area......experts chime in, "oh no that's not accurate enough, plants don't use the full spectrum silly, you need to calculate PAR values because that's what the plants actually use" ok bit of faff but it makes sense....now you're saying PAR just means lumens or lux and what you want to measure is PUR.....a portion of the PAR?....