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Thread: "Cool" or "warm" fluorescent lights?

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    moonflower's Avatar
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    "Cool" or "warm" fluorescent lights?

    I've been curious to know what the differences are to plants... I had been using a warm (yellowish) compact fluorescent for my CP's for the longest time, and when that finally burned out I got a "cool white" bulb (more in the blue family, i think), not realizing how different they looked. Is either one better/worse for plants? I've been thinking of getting another light for my itty bitty orchid collection too, and I wasn't sure which lights worked better. I've had the cooler light on my CP's for a while and they don't seem bothered... my pings have decided to flower like crazy but I'm not sure if that's the lighting or the wacky temperatures in my dorm room

    Thanks!
    "Seeds? Oh yeah... sometimes I forget they grow from those. I feel like they should hatch or something."

    ~a friend's observation of my CP's

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    Capslock's Avatar
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    I've always been under the impression that cool white is closer to the spectrum of sunlight. Thats' what I use, however, in my T5 fixtures with four tubes, I use three cool white and one warm white.

    Max
    Malo Periculosam Libertatem Quam Quietum Servitium

    My photos are copyright-free and public domain

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    herenorthere's Avatar
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    Personally, I don't think most plants care, but some physiological processes, such as flower bud initiation, might not begin without the right lighting. Rather than try to figure it out, I use it as one of my convenient excuses for why particular plants never blossom and so on. The only thing more important than a good lighting system is a good excuse for when things don't go right.
    Bruce in CT

    Madness is something rare in individuals — but in groups, parties, peoples, ages it is the rule. Friedrich Nietzsche

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    OMG h8 pings MrFlyTrap2's Avatar
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    If you look at grow lights there seems to be two types. A vegetative type and flowering type. The vegetative ones are suppose to spur healthy growth of the plant with the blue end of the spectrum, while the red end of the spectrum often makes plants want to flower. That would be closer to your older bulbs. Warm bulbs are usually more dim though when it comes to fluorescents. But anyways, that's why you'll see people mix the two bulbs in grow lights, it gives a more balanced output of light in both spectrums.
    My Grow List

    "It is only by studying nature that can we ever hope to defeat it."

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    swords's Avatar
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    Cool white is 4100K (color temperature rating) and warm white is like 2700K (at least roughly), While "daylight" bulbs are 6500K - though the noonday tropical sun at the equator is pretty much right around 5000K. So yes, cool white is closer to daylight.

    I am guessing you're using the "twisty" type compacts? They have packs of 3x 26Watt Daylight twisty compacts at Walmart for $7.
    If not using twistys they also sell 4 foot long 40 watt daylight tubes and another excellent tube called "Sunshine" which comes in a very obnoxious bright orange sleeve with yellow lettering. This tube is 40 watts and 5000K with a color rating index of 90 or 91 so it's almost exactly tropical sunlight colored. I preffer the 6500K Daylight twistys and tubes myself because the sunshine ones have a "golden" light and plants photograph better under the daylight tubes and grow just as well provided you are giving them enough lumens to begin with.


    It's not uncommon for plants to bloom soon after a bulb change, it's like spring time for a terrarium, the "sun" gets more intense (new bulbs are brighter than the old ones) and that kinda spurs them on. Temp swings will do that too, if a plant gets too cold for it's normal range (but not to a dangerous low) it will often inspire blooming - this is how many orchid show people get their plants blooming on the day of the show by using wild temp swings a number of weeks before a show.

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    I use the warm ones I prefer them hands down,
    they put out much more heat than the cool white ones though....

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    Illinois droseraguy's Avatar
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    To each their own it looks like, confused yet ? My choice is the Cool White from Menards in the box of (10 or 12 ?) T12's. On sale they are about $16 a box. Everything blooms according to the temp. and photoperiod supplied. My 2 cents !
    Only two defining forces have ever offered to die for you, Jesus Christ and The American G. I. One died for your soul, the other for your freedom.
    Romans 10: 9-13
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    --Freedom Czar-- Fryster's Avatar
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    The two new sets of T12’s I just installed last month in my grow-rack are all GE Plant & Aquarium lights.

    I decided on special plant lights after some online research. The cool white bulbs that so many people are using are radiating a spectrum of light that plants cannot use, too much in the yellow and green range. The cool white bulbs look great to us but to plants not so much…

    See here for example: FLUORESCENT PLANT LIGHTING

    I really like how Wayne did his own experiments on fluorescents. Anecdotal evidence though it be, what he has shown really makes sense.
    Only a moral and virtuous people are capable of freedom; the more corrupt and vicious a people becomes, the more it has need of masters. -- Benjamin Franklin

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