TeaTreeOil
Well-Known Member
So you've probably heard it a thousand times, or more. Lumens per square foot and how it matters so much. Well, it doesn't, really.
There's this awful comparison chart going around. It compares HPS(400w) with T5, CFL, T12, and incandescent. How does it do this? With lumen output alone. Why is this an awful comparison? Because they don't emit anywhere near similar spectra.
Here's the basic reaction spectrum of photosynthetically usable/active radiation.
And a couple bulbs:
Incandescent:
HPS:
I dare not even give an example of a fluorescent(a couple are included in the attachments, a GE warm white and a GE daylight, just because those are the most popular), as they are far too diverse and versatile, from disinfecting UV lamps, to actinic, warm white, daylight, Gro Lux, etc.
Have a look: http://ledmuseum.home.att.net/spectra7.htm
Where do you want peaks? Anywhere from 400-500nm is great, and 600-700nm too. From 500 to 600(peak HPS output), not the best, but this is the peak range for lumens. And lumens are for humans, not plants.
Lumens are only a valid comparison tool when comparing identical bulbs that vary only in wattage. That means the same manufacturer, the same color temperature, etc. Otherwise they are not comparable, and can be wildly inaccurate(over 100% difference). Case in point: low pressure sodium, 200 lumens per watt, horrible for plant growth as it has a monochromatic spectrum.
Additional reading(this one page sums it all up nicely): http://www.sunmastergrowlamps.com/SunmLightandPlants.html
More bulb spectrographs here: http://ioannis.virtualcomposer2000.com/spectroscope/amici.html
More about lumens and the sun's radiance: http://www.handprint.com/HP/WCL/color3.html
Happy growing.
There's this awful comparison chart going around. It compares HPS(400w) with T5, CFL, T12, and incandescent. How does it do this? With lumen output alone. Why is this an awful comparison? Because they don't emit anywhere near similar spectra.
Here's the basic reaction spectrum of photosynthetically usable/active radiation.
And a couple bulbs:
Incandescent:
HPS:
I dare not even give an example of a fluorescent(a couple are included in the attachments, a GE warm white and a GE daylight, just because those are the most popular), as they are far too diverse and versatile, from disinfecting UV lamps, to actinic, warm white, daylight, Gro Lux, etc.
Have a look: http://ledmuseum.home.att.net/spectra7.htm
Where do you want peaks? Anywhere from 400-500nm is great, and 600-700nm too. From 500 to 600(peak HPS output), not the best, but this is the peak range for lumens. And lumens are for humans, not plants.
Lumens are only a valid comparison tool when comparing identical bulbs that vary only in wattage. That means the same manufacturer, the same color temperature, etc. Otherwise they are not comparable, and can be wildly inaccurate(over 100% difference). Case in point: low pressure sodium, 200 lumens per watt, horrible for plant growth as it has a monochromatic spectrum.
Additional reading(this one page sums it all up nicely): http://www.sunmastergrowlamps.com/SunmLightandPlants.html
More bulb spectrographs here: http://ioannis.virtualcomposer2000.com/spectroscope/amici.html
More about lumens and the sun's radiance: http://www.handprint.com/HP/WCL/color3.html
Happy growing.
