Another boring light question

I'm still running normal 30W Fluorescent tubes in my 120x60x40cm tank. I need to replace them...so i did a bit of reading to try and understand the whole setup.
Please correct me if i'm still in the dark.

Everyone talks about the ?watt light setup. Should i rather not look at lumens instead of watts?
Quote from website -
" To understand this, it's important to know the difference in lumens Vs watts. A Lumen is standard unit of light as it is perceived by the human eye. Essentially, it will tell you how bright something is, unlike a watt, which is actually a measurement of energy consumption or output. The lighting industry has standardized ways that it measures the total emission of light from a product and include it on most packaging."

"Lumens to watts calculation formula

The power P in watts (W) is equal to the luminous flux ΦV in lumens (lm), divided by the luminous efficacy η in lumens per watt (lm/W):

P(W) = ΦV(lm) / η(lm/W)
So
watts = lumens / (lumens per watt)
or
W = lm / (lm/W)
Example
What is the power consumption of a lamp that has luminous flux of 900 lumens and luminous efficacy of 15 lumens per watt?
P = 900lm / 15lm/W = 60W"


From OSRAM:



So i can have low watts(say 30W), but high lumens/bright light in the tank?

 

short answer is yes, long answer - we should actually be talking about PAR at substrate.

Later Ferdie

 

Easier. If you want high light for your 120x60x40 tank get 4-6×54w t5 lights. Medium light 22x5w t5 lights

 

Yes you can put a 30W bulb in with more lumens that will give you more light but if the spectrum is wrong you might as well try and light it with a candle.

 

thanks guys for helping the newbie

 

Yes, i understand...looking at 6500K

 

Most plants will actually work under any Kelvin rating. They adapt.

 

Don't know so much about that statement. Plants do well with a certain type and amount of light light. Unlike fish they cannot adapt if you add a plant that requires a high amount of light in a tank with a low amount of light it either dies or becomes stunted. Also when a plant requires a high amount of light it also requires more CO2 and nutrients.

 

Swag, sorry m8 but I think you are once again misunderstanding this entire concept.

The kelvin rating is the colour temp and plants adapt to the kelvin rating they are placed it, no like a fish adapts to harder or softer water but they dont suffer from not having a dedicated 6500-6700K on them. If you place 10000K in there they will grow exactly the same. This I have discussed with many a person who regularly enter international aquascaping comps and place within the top 100 in the world.

High light plants are a different matter completely and Klevin ratings have very little to do with these.

 

Okay so what you are saying is if you had two tanks one tank with a kelvin rating of say morning light and one with say a kelvin rating of midday sun and you let the plants grow out in these tanks and then swap the lights around that the plants will adapt and keep on growing like they did orginally? With no growth rate changes at all?

 

Your still not getting it. Kelvin is not par ratings eg. Penetration.

 

Greystoke has done a allot of work on this topic ...

google Greystoke Topic: What's next after "Watts per gallon"

some really good reading and links to external forums.

Later Ferdie

 

So if I understand it correctly: 2700k is late afternoon colour light, a few hours before sundown. 6700k is Noon colour light on a blue sky cloudless day at the equator. (most aquarium plants are from equatorial regions of our planet) So, if you were a plant submerged under a foot of water what type of light do you think you might prefer for gorwing? That said, shorter wavelength blue light penetrates much farther into the water than the longer wavelength red. This may be why 6700k+ Kelvin bulbs seem to be better for plant growth, since the blue light is more readily available for the plant to use compared to the lower Kelvin lights. And if I remember my biology classes the blue and red zones of the visible spectrum are the most beneficial to plants.

Obviously colour temperature is not the only thing that needs to be good in a light, the amount of PAR/Lux/Lumen is also important. You cant have a light with the right colour temperature but with the incorrect PAR/Lux/Lumen and vice versa. But if you buy a proper branded light which the spectrum falls between 5000K and 6500K (They are usually called full spectrum lights) these are pretty good for plant growth. Also plant leave development is very dependant on blue light spectrum while stem growth is dependant on red light spectrum. So having a mix of both would be ideal. And also if it is a display tank having a green light in the spectrum will make the plants stand out more but that is only for display purposes.