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#### toffee

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To help me understand, what would my LSI (lux per sq inch) be if I have a bulb that is rated at 2000 lumens and use it on a tank with a surface of 1' x 1' (144 sq. inches). This is not factoring in the lost, reflector, color temp etc. and just assume 2000 lumens would be available.

thanks for helping.

#### retoid

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This will help you.
http://en.wikipedia.org/wiki/Lux

I may be way off cause i suck at math but would 8000lux be correct? Meaning it would be 55.5LSI?

Lux versus lumen

The difference between the lux and the lumen is that the lux takes into account the area over which the luminous flux is spread. 1000 lumens, concentrated into an area of one square metre, lights up that square metre with an illuminance of 1000 lux. The same 1000 lumens, spread out over ten square metres, produces a dimmer illuminance of only 100 lux.

#### toffee

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Don't think 2000 lumens can translate into 55.5 LSI. As that would be extremely high light according Rex's guide:

So what I am going to propose is that instead of thinking in watts per gallon we instead think in lux per square inch. Or LSI. And let's look at these figures based on a 55 gallon tank with 110 watts of light (low light), 160 watts (medium light) and 220 watts (high light).

* Low light is 15 LSI
* Medium light is 22.4 LSI
* High light is 30 LSI

And since those are hard numbers let's instead make them ranges.

* Low light is 12-17 LSI
* Medium light is 20-25 LSI
* High light is 28-32 LSI
* Very high light is over 35 LSI
http://rexgrigg.com/mlt.html

I am getting 13.88 or 14 LSI, not sure if that is right though.

#### defdac

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To help me understand, what would my LSI (lux per sq inch) be if I have a bulb that is rated at 2000 lumens and use it on a tank with a surface of 1' x 1' (144 sq. inches). This is not factoring in the lost, reflector, color temp etc. and just assume 2000 lumens would be available.
thanks for helping.
Lux is lumens per square metres.

If you have a tube without reflectors that omni-directional emits 2000 lumens only about 25% will go down the tank.

So about 0.25*2000 = 500 lumens will reach the 1'x1' square.

144 sq inches = 0.09290304 square metres

So if you manage to put down about 25% of the 2000 lumens on 0.09290304 square metres you get about 5400 lux which should translate to about 37 lux per square inch.

If this is a, for example a Philips 865 T8 bulb this translates to about 84 mmols/m2 PAR at the bottom or about 43 mmols/m2 PUR.

A normal hightech tank (like those Oliver Knott is running) has about 230-250 mmols/m2 PAR or 120-130 mmols/m2 PUR.

If you put on a reflector that diverts like 80-90% of all the 2000 lumens and have a 865 bulb you will get about 290 mmols/m2 PAR or 150 mmols/m2 PUR.

Calculations made with an upcoming calculator I've made: http://82.183.138.227/GTKTest/GTKTest.html

#### toffee

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Linkoping! A saab engineer?

Back to our fish talk. My tank is actually quite big, but I only have 2 plants in there so I am using two of these bulbs with reflector sitting about 3 inches from the water and right on top of the plants.
http://www.discountbulb.net/top/us-30w.php

Based on your calculation, I have 37 Lux per sq inch. That would put it in the high light category under Rex's guide. Since I am not dosing CO2, that could create a CO2 deficiency. And indeed, the two plants are wilting.

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