Lighting Question

EmilyMarie85

EmilyMarie85

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Aug 16, 2010
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Boise, ID
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Emily
K so - I have a 24" T8 Flora Sun 8500k light on my 30g tank -- which to my understanding gives me border line "medium light"... what would happen if I put a 24" T6 11000k light on the same tank -- would it still be considered the same light level, since its T6 and only 20 watts? Sorry, I am all confused right now...

Thanks
Em
 
Little bit of florescent light basics.

The 8500K and 11000K refer to the color spectrum that the light produces. Generally the lower the K rating the more toward the red spectrum and the higher the more toward the blue spectrum. Most plants need both areas to grow well so 5000-6000k lights are recommended.

T12, T8, T6, T5 etc... refer the the efficiency of the lamp to produce light based upon wattage. If the bulbs are the same length they generally produce close to the same amount of light. The smaller the number next to the T corresponds to the bulb using less energy (Watts) to produce similar amounts of light.

So what would happen if you placed a T6 11000K bulb over the tank. Well strangely enough you would be giving your plants less amounts of light that they actually need. This kind of light is designed for corals (reef tanks) that use mainly the blue spectrum of light.
 
T = 1/8"

t2 = 1/4" (2 X 1/8")
t5 = 5/8"
t8 = 1"
t12 = 1.5"

thinner bulbs produce more light per watt since the electricity is forced to react with more of the gas in a more confined space (limits the path of least resistance). as well thinner bulbs create better reflector efficiency making it possible to direct more of the light downward where you need it. the reason why the reflectors are more efficient is there's less bulb in the way blocking the light from going straight down.

degrees kelvin refers to the color the light produced by a specific bulb looks to the human eye.

what k ratings are best is a moot point afaik. different bulbs produce different light in different quantities. the k rating of a bulb is highly dependent on human visual perception... which does nothing for plants. there are bulbs rated pretty high on the kelvin (k) scale that produce good par (photosynthetically active radiation [light that plants can use for photosynthesis])... but above 10,000k they may be few and far between, idk. 6700k and 10,000k are generally suggested because they're safe bets not only for growing plants but also for being visually pleasing to the eye.

the terms "daylight" and "full spectrum" are widely used for many bulbs that are good for growing plants and provide a wide variance of light "colors" that should suit plants well.

your t6 bulb might not even fit into your t8 fixture.

both your t8 and t6 bulbs seem a bit short on light for your 30 to me. 2 bulbs might do the trick, but i suspect 3 or more would be better... or 2 4' shop light bulbs.

THE V posted good info, too. hopefully this gives you a little more insight. however... i'm not sure about the 11,000k bulb... i've not heard of one being used for plants of any kind before...
 
IMO, T8 bulbs are not effective in any tank over 16 inches tall. Two T8 bulbs don't compensate for it either.

What I would do:
1 - T5NO bulb will give you low light
2 - T5NO bulbs for medium light
1 - T5HO bulb for medium light (raise it a few inches above the tank for low light)
 
i didn't even consider height. good point, coach.
 
I have been re-researching lights for my tank. I would like to replace my 130W Coralife Compact Flourescent fixtures with something different (T5HO), having a 29 gallon tank myself makes lighting it darn difficult. (note to OP: I have a high tech high light co2 injected tank so my needs are quite different)
 
coach_z said:
I
1 - T5HO bulb for medium light (raise it a few inches above the tank for low light)
Click to expand...

Out of curiosity. I have read stuff about it being good to have the light raised above the tank because it gives the light an area to spread out before it goes into your tank. This spreads out the light equally to all parts of the tank.

If you have 1 t5ho on a 30 gallon that is raised 4 inches above would that be low light or does it have to be raised more than that?
 
rockhoe14er said:
Out of curiosity. I have read stuff about it being good to have the light raised above the tank because it gives the light an area to spread out before it goes into your tank. This spreads out the light equally to all parts of the tank.

If you have 1 t5ho on a 30 gallon that is raised 4 inches above would that be low light or does it have to be raised more than that?
Click to expand...
Not an expert on answering this question, but here it goes:
Of the light that hits the water in your tank a certain percentage reflects away and out of your tank. Ever look at a lake or ocean at sunset and get blinded by the reflection?? This reflection weakens the intensity, PAR, etc that is able to make it to the bottom of the tank.

Yes, it does allow the light to spread out a little bit further, but really how much? The closer the light, the more 'intense' it will be at the surface of the water allowing it to penetrate deeper. The light is going to spread out one way or another (either in the water or before the water).

How much it spreads over 4 inches, i dont know. It will depend on the reflector, the bulb, water level, substrate height. I am sure if you whip out your TI-82 plus you can figure it out using the angle of your reflectors, height of your tank, take into account your substrate and then the height of you and then calculate the length of some hypotnuses etc. I also imagine that at a certain height above your tank you simply start illuminating the floor of your room, and the walls that surround your tank.

Speaking of substrate i didn't mention earlier that the depth of your substrate is crucial in this calculation. uh....more on that later.

(upon reading this further i dont really know if any of this made sense....i am just blabbering right now).
enjoy the show!
 
Here are my thoughts on the subject.


If i have the light right on top of the glass then the upper part of my tank in the corners won't get any light. because a fish tank light will spread in the Upsidedown V path because of the reflectors around the light.... but if you raise the light a little then you give the light time to spread out so that it can hit all those parts of the tank equally.

Furthermore when the light is right on top of the tank this also makes for un even light distribution because the center right under the lights will have the greatest intensity while the sides will have less and the top corners will have even less.

So if a t5 bulb is sitting right on top i feel only the center of the tank will be medium light and everywhere else will be medium low light.
 
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