Please help with Fluorescent Light

[Undergrounder]

I keep reading all this hoopla about T5 fluorescents, so i went up to my local hardware store and saw a couple of them on display. Just judging from what i could see, they didn't seem nearly as bright as the 'tri-phosphor' regular T8s which seemed the brightest. Should i still go for the T5s?

Also there were T4s! Are T4s even better or something? I understand that T represents the diameter of the bulb but are all T5s better than all T8s for instance?

[gixrj18]

I don't think that the T5's being discussed are the same ones you're seeing at the hardware store. The ballast may be similar, but the bulbs are specifically for growing. I have only seen these at hydroponics stores, or on line. They are a different spectrum than the ones at the hardware store.

[Ross]

Originally Posted by Undergrounder

I keep reading all this hoopla about T5 fluorescents, so i went up to my local hardware store and saw a couple of them on display. Just judging from what i could see, they didn't seem nearly as bright as the 'tri-phosphor' regular T8s which seemed the brightest. Should i still go for the T5s?

Also there were T4s! Are T4s even better or something? I understand that T represents the diameter of the bulb but are all T5s better than all T8s for instance?

I agree with the previous post. I am not aware of a true t4. I have seen and used t5, t8, and t12. There, supposedly is a t6 available (see Maxum 5000 47" F54-T5HO Mini Bi-Pin) I can't say anything about this tube, even though I have lots of this company's CF bulbs. The t5 technology is entirely different from the supposed cool tubes of t8 and t12. The High Output (HO) t5 is designed to operate most efficiently at 35 degrees C (95 degrees F). The other technologies are cooler (I don't recall what temps). There are also high efficiency t5's (not real commonly available) that are much lower light output. Yes some t8's can appearbrighter but check the lux output (or lumens). The mean lumens for a new t5 HO tube (47") is 4560-5000. The bulbs in the refernece above are supposedly 5200 lumens. t8 are approx 3000-3300 lumens and the t12s are approx 2500 lumens. Also the color temperature is a factor. You can purchase all sorts of balanced bulbs in any of the 3 technologies. 6500K bulbs appear lots brighter than 3000K bulbs even though lumens are equal. Compare the above figures to a typical HPS bulb which puts out approx 10,000 lumens. It sounds like a lot, but typical installations use one of these HID lamps (150 watts) and a typical t5 bank is 4 - 47" tubes (they're referred to as 48" but actually 47" long) and 20,000 lumens. The HPS lamps run HOT while the t5's are just warm - easier to control the heat. This is why so many of us are excited about t5's. Hope this answers your questions.

[IdahoOrchid]

Ross, so the tubes output are additive? At what distance from the tubes and/or bulb is the output value measured? 1" comes to my memory for some reason. Where along the tubes length is it measured. I ask this because I have read that as you move from the center toward each end the output diminishes.

Does adding a reflector over the tubes increase the effective output of the fixture? If so, is white or a shiny surface preferred?

[Ross]

Originally Posted by IdahoOrchid

Ross, so the tubes output are additive? At what distance from the tubes and/or bulb is the output value measured? 1" comes to my memory for some reason. Where along the tubes length is it measured. I ask this because I have read that as you move from the center toward each end the output diminishes.

Does adding a reflector over the tubes increase the effective output of the fixture? If so, is white or a shiny surface preferred?

Steve, yes they are additive. It's the collective light you are after. The distance you are concerned with is the distance of the leaf surface from the bulbs. So, if taking a light meter reading (direct reading - not reflected from leaf surface,) then you want the sensor to be near the leaf surface. If all you want is a measure of how much light the tubes are putting out, then anywhere near center is fine. But most folks here are concerned with whether the lights are doing the job. So the reading should be near leaf surface.

In answer to reflector, the obvious answer is yes. The more reflective the better. Most high def t5 fixtures today have highly reflective surfaces designed to reflect and concentrate the most amount of light possible downward. Hydroponix growers use reflective mylar (which comes in rolls) for the same reason. The more you can bounce light back to the target, the better. Even aluminum foil will work.

<I ask this because I have read that as you move from the center toward each end the output diminishes.>

Most hi-tech florescent tubes (like t5) are pretty constant over the length of the tube, but it should be obvious that there is a zone at the ends where light diminishes rapidly. I recommend that the fixture one selects be longer than the intended application by at least 3" on each end. If that's not feasible, then consider multiple banks of lights.

[dougd]

I have a setup in the basement for the Winter. I use T8 Daylight with a 6500K spectrum on a timer. They work just fine. I found them and the fixtures at Lowes for less than $25.00.

[Ray]

Tube diameter is not the only thing that affects how well a bulb works. To understand what's going on with fluorescents, you need to understand how they work. Rather than reiterating it, read this very simple explanation: Howstuffworks "How Fluorescent Lamps Work"

Having a smaller diameter means a smaller volume of gas to ionize, hence the "energy savings". That, however, does not necessarily translate to "higher efficiency", as a smaller diameter bulb has less surface area, so less total light output. Also, two bulbs of the same diameter, but driven with different power levels (wattage) will also have different output levels.

Then you throw in the specific phosphor blend, and that determines intensity and spectrum. FWIW, I have had great luck with bulbs having the "Chroma 50" phosphor blend.

Then you have to add the efficiency of the reflector, and it's ability to scatter the light being emitted from the "back side" of the bulb.

Also, if I remember correctly, when it comes to light bulbs, the specified light intensity is given for one foot from the bulb, meaning that at 6" (1/2 the distance) it is 4-times as intense, and at 2 feet, it is 1/4th so.

[Ross]

Originally Posted by Ray

Also, if I remember correctly, when it comes to light bulbs, the specified light intensity is given for one foot from the bulb, meaning that at 6" (1/2 the distance) it is 4-times as intense, and at 2 feet, it is 1/4th so.

Sort of. If you are refering to "foot candles", then yes, sort of. Lumens (or more recently, Lux) actually is a measure of light output, thus measured at the bulb. Here is a quote from Wikipedia:

Lux versus footcandle
One footcandle ≈ 10.764 lux. The footcandle (or lumen per square foot) is a non-SI unit of illuminance. Like the BTU, it is obsolete but it is still in fairly common use in the United States, particularly in construction-related engineering and in building codes. Because lux and footcandles are different units of the same quantity, it is perfectly valid to convert footcandles to lux and vice versa.

The name "footcandle" conveys "the illuminance cast on a surface by a one-candela source one foot away." As natural as this sounds, this style of name is now frowned upon, because the dimensional formula for the unit is not foot · candela, but lumen/sq ft. Some sources do however note that the "lux" can be thought of as a "metre-candle" (i.e. the illuminance cast on a surface by a one-candela source one meter away). A source that is farther away casts less illumination than one that is close, so one lux is less illuminance than one footcandle. Since illuminance follows the inverse-square law, and since one foot = 0.3048 m, one lux = 0.30482 footcandle ≈ 1/10.764 footcandle.

In practical applications, as when measuring room illumination, it is very difficult to measure illuminance more accurately than ±10%, and for many purposes it is quite sufficient to think of one footcandle as about ten lux.

Most sources like GE or Philips refer to Lumens or LUX when specifying the light output of their bulbs.

[newflasker]

Originally Posted by dougd

I have a setup in the basement for the Winter. I use T8 Daylight with a 6500K spectrum on a timer. They work just fine. I found them and the fixtures at Lowes for less than $25.00.

Hi Dougd,
The price is good. I want to setup in my basement too but I am afraid that my basement is too cold (my living room is about 72, basement is about 68). What is the temperature in your basement?

[IdahoOrchid]

Doug, what is with the leaves in the 5 gallon bucket????