Wow, lol, I’m not sure about the way the beginning of the quote of me starts, lol, I don’t remember making any of those typos either, and it was a little out of context as well, ha ha. But otherwise I think the collection mostly gets the points across…
Here is a summary of the same thoughts I saved myself, as it is fairly comprehensive and is understandable even out of context of the original reply. This is a common source of much confusion for new growers and I hope this will clear some things up.
A post and reply to a similar question:
"I wouldn’t use a typical or traditional incandescent light, not enough blue light to keep a plant healthy.
For flowering you want about ideally 50 watts per square foot with horticultural HID lights for indoor growing. You can probably get away with a little less than 50% for veg. So about 25 watts per square foot would probably be plenty, for veg.
For fluorescent lights, especially CFLs and T5s, and even more so for these lights when specifically designed for plants, 40-45 watts per square foot is enough for flowering. Keep in mind, part of the reason you can get away with less watts is because you can bring fluorescent lights closer, as they don’t create as much heat at the bulb as HID lights do, and so the lumens are more intense due to proximity and the inverse square law of radiation, not because they create as many lumens/PAR per watt at the bulb. A note to keep in mind especially about “household CFLs”, is we are talking actual watts, not equivalent watts.
With good quality LEDs made for plants you can get as low as 30-35 watts and still be efficient and effective for flowering. But that is because you can turn nearly 100% of the watts into only PAR. PAR stands for photosynthetically active radiation, and refers to all the wavelengths of light between 400 nm (violet, blue) and 700 nm (deep red). White light is roughly made up of equal parts red, green and blue light. In simple terms plants only need the blue and red light and so you can effectively save up to a third of your electrical watts by not wasting it on green light. Most of the green light is not used and is reflected away from the plant, this is why plants are green, they are reflecting the green part of the spectrum away and into your eyes. LEDs generally are not as hot as HIDs either, and some of the increase in efficiency could also again be due to proximity and the inverse square law that describes the diminishing intensity of radiation over distance.
Here is a list of needed lumens:
Seedlings and clones require about 400-1000 lumens per square foot.
Vegetative growth requires about a minimum of 2,000 to 3,000 lumens per square foot.
Flowering requires about 5,000 to 10,000 lumens per square foot, ideally, and can take possibly much more.
10,000 lumens is supposed to be about the average power of the sun at sea level on a clear day at high noon. 8,000 – 12,000 lumens is supposed to be about the average power of the full sun without any overcast or no clouds, depending on altitude and potentially other factors. In the high altitudes of the Himalayas and Hindu Kush mountains (the ancestral home of cannabis), this means probably leaning towards the higher numbers on a clear summer day as there is less atmosphere to filter out some of those lumens.
It’s not ideal, but you can make do with 2,000 lumens for an entire grow if necessary.
High pressure sodium (HPS) is heavy on the red side of the spectrum but has enough blue to keep your plant healthy through all phases of growth.
HPS has color rating of about 2700K. Plants can use more red than blue, and will stay healthy as long as about 20-30% of the light comes from the blue spectrum, and so this is why HPS does such a good job for growing even though it doesn’t match the ratio naturally found in sunlight. HPS still has plenty of blue and other colors or it wouldn’t look like yellow/orange-ish, but still mostly white-ish light. White light is roughly made up of equal parts of red, blue and green light.
Metal Halide (MH) can be better tuned to a closer spectrum matching natural sunlight but is not as efficient in the conversion of watts to PAR as High Presure Sodium (HPS), so you get more bang for your electrical watt with HPS.
LEDS are among the most efficient as they can deliver specifically PAR only, and no other parts of the electricity is wasted on non PAR parts of the electromagnetic spectrum, and effectively as much as a third of the watts is not wasted on the green spectrum.
Most commonly found in MH and fluorescent lights you’ll see a color rating based on the “Kelivin” color scale, the higher the number the more “cold” or blue/violet the light looks and in general the more of this side of the electrical magnetic spectra is represented, the smaller the number the more “warm” or orange/red the light looks and in general more of this side of the electrical magnetic spectra is represented.
5500K to 6000K is the color of sunlight at high noon and is generally considered pure white or true white. 5000K to 6500K is the color of sunlight with various other conditions, including just before sunset and still bright(5000K) and overcast and kind of bright(6500K). Yes, the more exact color might change depending on altitude, possibly latitude as well as season, as this will change the amount of atmosphere the sun goes through and more atmosphere may further yellow or redden the hue of the sunlight, not unlike the way sunsets are more orange or red than the way the sun looks most pure white at high noon(5800K) when it is passing through the least amount of atmosphere.
Here is a break down of the electrical magnetic spectra near the photosynthetically active radiation, or PAR, range:
720 - 1000 nm There is little absorption by chlorophyll here. Flowering and germination is influenced. At the high end of the band is infrared, which is heat.
610 - 720 nm This is the red band. Large amount of absorption by chlorophyll occurs, and most significant influence on photosynthesis. (promotes flowering and budding)
520 - 610 nm This range includes the green, yellow, and orange bands and has less absorption by pigments.
400 - 520 nm This range includes violet, blue, and green bands. Peak absorption by chlorophyll occurs, and a strong influence on photosynthesis. (promotes vegetative growth)
380 - 400 nm Start of visible light spectrum. Process of chlorophyll absorption begins. UV protected plastics ideally block out any light below this range.
315 - 380 nm Range of UVA ultraviolet light which is neither harmful nor beneficial to cannabis plant growth. Although some studies do seem to indicate this band might stimulate resin production, as THC does seem to have UV blocking properties, and these frequencies may be able to stimulate the plant to create these UV protecting resins without actually having toxic or negative effects on the plant’s biological function.
280 - 315 nm Includes harmful UVB ultraviolet light which causes cannabis plants colors to fade.
200 - 280 nm UVC ultraviolet range which is extremely harmful to cannabis plants because it is highly toxic.
And above these wave lengths dwell the very long radio/TV waves (even microwaves), and below it resides the ultra short X-rays and gamma rays.
It is a lot of info, but I think I got you covered in most ways I could think of pertaining to your questions."
I hope this complete excerpt makes things a bit more clear and helps out.
If you have any questions or clarifications needed, feel free to ask.