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Lumens vs. Watts


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#1
tinman94

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What really grows the plants more watts or more lumens. Im asking this because i dont know what size HPS light i need to flower 4 plants. I know they say 100 watts per plant and it would be cheaper to buy 400 watts of cfls then 400 watt HPS. I know HPS has more lumens so do i need as much watts then.

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#2
skyler21

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I havent had any experience with HID lighting but I have with CFL. CFLs will def. be cheaper, but an HPS will penetrate the canopy better and grow fatter buds IMO. so it all depends do you have the $ to dish for a HPS? if so i would go with that but CFLs are always an alternative and work quite well for me. I would definately buy an HID system if I had the money to tho...

#3
grass69

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The 400W MH/HPS will be much better then 400W of fluros.

#4
G-lant

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that didn't answer his question, I have the same question. because I have the opportunity to get 5million lumen light, or a 12mill Lumen light. so is it lumen or is it watts?

#5
puff

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lumens does. The closer you can get the light to the plant without burning it (ie. air cooled - glass enclosed cases)the better and the more lumens. Also the more time you can put on the plant the better. For example I have purple kush under light atm and they can be forced to flower at 13 1/4 hours. I go 1/2 hour under that and am flowering this particular strain at 12 3/4 hours. This makes for larger happier buds and a happier me lol.

Good luck and good growing. :D

#6
toastybiz

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Neither. Both are measures of something other than what we really want to measure, actual light intensity, but it is difficult/expensive to measure that and there tends to be somewhat linear correlations between watts and lumens and actual light intensity (at least within the same kind of lighting) so we use those as shorthand.

Wattage is a measure of electricity consumption, that's all. Technically wattage has nothing to do with light (how much light does a 1000 watt hair dryer give off?), however if you are talking about wattage of bulbs, and the ratio of the amount of light given off by a certain type of bulb to the wattage it consumes is somewhat predictable, then sometimes we talk about wattage as if we were talking about light intensity.

Lumens is a measure of light intensity at a fixed distance of one foot on a fixed area of one square foot. Furthermore, lumens measures only certain (visible to humans) frequencies of light. But again, the relationship is somewhat linear so we often use the term lumens when talking about light intenstity. Lumens is getting closer to the concept, but in reality lumens is a standardized measure for comparing bulbs one to the other, not for measuring how much light is being given off.

For example, take a bulb rated at 10,000 lumens and move it half the distance closer to the plant, and what happens to the lumens? Nothing -- it's still a bulb rated at 10,000 lumens. But as we know that light intensity is inversely related to the square of the distance, moving the light to half the distance increases the light intensity four-fold.

Watch those rules of thumb such as 100 watts per plant. That's the shortcut I'm talking about, and if you use that rule of thumb when applying HPS lighting then your actual light intensity will be good. Most CFLs are less efficient than HIDs at converting watts into light, so you want to be higher in wattage when using CFLs and most definintely you only want to look at actual watts, not the "equivalent" watts printed on the package.

#7
cobirch2

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Neither. Both are measures of something other than what we really want to measure, actual light intensity, but it is difficult/expensive to measure that and there tends to be somewhat linear correlations between watts and lumens and actual light intensity (at least within the same kind of lighting) so we use those as shorthand.

Wattage is a measure of electricity consumption, that's all. Technically wattage has nothing to do with light (how much light does a 1000 watt hair dryer give off?), however if you are talking about wattage of bulbs, and the ratio of the amount of light given off by a certain type of bulb to the wattage it consumes is somewhat predictable, then sometimes we talk about wattage as if we were talking about light intensity.

Lumens is a measure of light intensity at a fixed distance of one foot on a fixed area of one square foot. Furthermore, lumens measures only certain (visible to humans) frequencies of light. But again, the relationship is somewhat linear so we often use the term lumens when talking about light intenstity. Lumens is getting closer to the concept, but in reality lumens is a standardized measure for comparing bulbs one to the other, not for measuring how much light is being given off.

For example, take a bulb rated at 10,000 lumens and move it half the distance closer to the plant, and what happens to the lumens? Nothing -- it's still a bulb rated at 10,000 lumens. But as we know that light intensity is inversely related to the square of the distance, moving the light to half the distance increases the light intensity four-fold.

Watch those rules of thumb such as 100 watts per plant. That's the shortcut I'm talking about, and if you use that rule of thumb when applying HPS lighting then your actual light intensity will be good. Most CFLs are less efficient than HIDs at converting watts into light, so you want to be higher in wattage when using CFLs and most definintely you only want to look at actual watts, not the "equivalent" watts printed on the package.


actually, your mixed up. lumens is strictly the amount of light the source puts out. it has nothing to do with distance. if you want to look at it like that, lumens is a measure of light the bulbs puts off at its surface, a value called luminous flux. the true way to measure the light an object is getting is through a quantity called illuminance, measured in lux. there is really no good way to measure the lux that your plant is receiving. light reflects off the walls, certain parts of the plant are farther away than others, all sorts of things come into play with a scenario like this.

but since each type of light has a recommended distance from the plant (CLF's one inch, HPS 14-20, etc) we can just use lumens as a good aproximation for the light our plant will be receiving. the more lumens the better, period. paint the inside of your grow box white, hang some reflectors around your bulb, and pile in as many lights as you can get without a fire starting. falling below about 3000 lumens makes for a bad plant. boost the lumens up to ten or twenty thousand with some HID lights and your set for a good plant with big juicy nugs.

#8
toastybiz

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it has nothing to do with distance.

Right, that's why I said that when you move a bulb rated at 10,000 lumens you still have 10,000 lumens even though the actual light intensity on the plant changes.


we can just use lumens as a good aproximation for the light our plant will be receiving.

That's what I said, though it's not an approximation since it isn't measuring illuminance, it's more of a substitute measurement or a short-hand for understanding it. Bottom line: the more lumens (of the right spectrum) the better, I agree.

#9
puff

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