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Thread: Switching from T8's to T5's

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    cwatson1414's Avatar
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    Switching from T8's to T5's

    Is there anything I should know? I've read around here that T5 bulbs put out a lot of heat, but I've also read they are very cool and can be put much closer to plants? I'm wondering what I will need to change when I make this switch, and I am finding a lot of contradictory information.
    Input from growers using T5 bulbs in a terrarium setting is much appreciated. Thanks, TF!

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    Av8tor1's Avatar
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    T5's run considerably hotter than T8

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    NECPS Editor Radagast's Avatar
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    My plants are grown under T5's and are over 12inches away from the lights. Probably more like 15 inches. The bulbs get pretty hot. My basement temps stay in the 50's but my grow rack temps are always in the upper 60's-70's because of those bulbs. Having the lights that far away from the plants has been nice, and allows the flower stalks to grow without getting burnt to a crisp...I found that out the hard way.

    I'd be interested to know more specs about your terrarium. I've seen people that hang the lights over the terrarium without setting it down on top of the rim of the terrarium, and point a fan aimed across the bulbs, and that helps with the heat.


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    I Am the Terror Of the Night! NemJones's Avatar
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    I use strictly t5s, they dont get terribly hot.
    My nepenthes grow about 12 inches away, i can pretty much put my hand on the bulb, but i wouldnt reccomend it
    Last edited by NemJones; 02-01-2016 at 12:30 PM.

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    nimbulan's Avatar
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    As I understand it, T5's are a bit more efficient but will produce much more light (and hence, heat) per foot, especially with T5HO bulbs. Each individual bulb will run hotter, but you need fewer of them to produce the same amount of light so you shouldn't run into heat problems as long as plants aren't touching the bulbs.

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    carnivorous plants of the world -- unite! DragonsEye's Avatar
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    You might consider trying LED tube lights. There are some made with a more useful plant spectrum in mind. They are a lot more expensive but run far cooler. Tubes have the usual prongs on either end of the tubes and can be used in a standard shoplght fixture. However, you would have to remove the ballast(s) from said fixture.
    "Blessed are the cracked….
    For they are the ones who let in the light."



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    Here is some numbers for the efficacy comparison among T8, T5NO and T5HO (system efficacy columns are more relevant).
    Does a T5 lamp give as much light as a T8 lamp? | What are T5 Lamps? | T5 Fluorescent Systems | Lighting Answers | NLPIP
    The efficacy is just lumen/W, but we want to know how much heat vs light is produced from each. This later quantity is related to radiant efficiency (i.e. what proportion of electric energy is converted to light). Since the energy not converted to light is released as heat, (1 - radiant efficiency) is basically the amount of heat produced. The emission spectra are similar among these 3, so we can consider that the radiant efficiency is proportional to the efficacy.

    When the ambient temp is hot, T5NO is more efficient than T8 and T5HO (which are similar to each other). When cooler, T8 is most efficient. This calculation is relevant when you have the fixture in an enclosure. But if the fixture is outside of the enclosure, then you need to consider the heat projected forward from the light (and the heat produced by ballast doesn't matter much). For example, HPS has a emission peak in infra red (around 800nm??), so it throws heat forward (this aspect is not captured by the radiant efficiency calculation). But all florescent light bulbs have relatively similar emission spectra, so the lamp wattage represents the amount of heat projected forward. 54W T5HO bulb will project about 1.7x more heat than 32W T8 etc. Basically I'm repeating what numbulan said above.

    DragonsEye, majority of T8LED (which are easily available) are direct replacement type, which doesn't require ballast removal. The ballast removal type has generally higher efficiency, though. Then there is a hybrid type which can be used with or without the ballast:
    T8/T10/T12 LED Light Tube, 4FT, Hyperikon, Dual-End Powered, Works with and without T8 ballast, 18W (40W equivalent), 2200 Lumens, 4000K (Daylight Glow), Clear Cover, DLC-qualified - (Pack of 4) - - Amazon.com
    This one has moderately high efficiency (higher than any fluorescent, but not the best among T8 LED).
    Last edited by naoki; 02-02-2016 at 01:16 PM.

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