Funny, I recall hearing about 10g planted with 2x15w CFLs over them, growing lots of stuff.
Lux, Lumens, Etc.
- Thread starter Nolapete
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Funny, I recall hearing about 10g planted with 2x15w CFLs over them, growing lots of stuff.
No this would be like saying a car that gets 40 mpg is the same as a car that gets 30 miles per half gallon. Lux is a measure of light per unit of area. thats why I kind of missed the part where you asked for lux per square inch, which is kind of like asking for miles per gallon and then asking for the translation to miles per gallon per quart.
EXACTLY!
lux = lumens/sq.meter
"lux per square inch" would mean "lumens per square meter per square inch"
It is a completely nonsensical term! GAHHH! FUZZY MATH! *runs away*
No, because 1 lux = 1 lumen per square meter or 1 lux = 1 lumen per 1550 square inches.
1 square meter = 1550 square inches
864 square inches is inside of 1550 square inches, so the same value is for both.
You have an umbrella that covers 1 square meter. It still only covers 1 square meter whether the people under it take up 864/1550 square inches or 1550/1550 square inches.
Lux per square inch isn't a nonsensical term. It is the conversion of the square meter part of lumen per square meter to square inches by which we measure our aquariums surface area.
Lux per square inch is the same thing as saying that 40 mpg is 80 mp half gallon. The amount of gallons doesn't change. The unit of measure is all that changes.
If I have a 75 gallon tank and I only fill it up half way, it still has 864 square inches of surface area. If I only have 75% of it planted, the surface area doesn't change either.
I was hung up on the conversion of lumens per square meter to lux per square inch thinking that the lux value increased because the area it was covering was smaller. This would make it impossible for the bulb manufacturers to have any measurement that follows a standard.
I realized that when they rate a bulb for lumens they are also rating it for lux. Since there's a 1 to 1 ratio (1 lux = 1 lumen per square meter), my logic that the lux value would increase was incorrect.
1 square meter = 1550 square inches
864 square inches is inside of 1550 square inches, so the same value is for both.
You have an umbrella that covers 1 square meter. It still only covers 1 square meter whether the people under it take up 864/1550 square inches or 1550/1550 square inches.
Lux per square inch isn't a nonsensical term. It is the conversion of the square meter part of lumen per square meter to square inches by which we measure our aquariums surface area.
Lux per square inch is the same thing as saying that 40 mpg is 80 mp half gallon. The amount of gallons doesn't change. The unit of measure is all that changes.
If I have a 75 gallon tank and I only fill it up half way, it still has 864 square inches of surface area. If I only have 75% of it planted, the surface area doesn't change either.
I was hung up on the conversion of lumens per square meter to lux per square inch thinking that the lux value increased because the area it was covering was smaller. This would make it impossible for the bulb manufacturers to have any measurement that follows a standard.
I realized that when they rate a bulb for lumens they are also rating it for lux. Since there's a 1 to 1 ratio (1 lux = 1 lumen per square meter), my logic that the lux value would increase was incorrect.
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You wouldn't ask for miles per gallon per quart. You have to convert to quarts first and ask for miles per 4 quarts.
I'll concede that lux per square inch isn't the best way to describe this theory.
I think you'd misunderstanding something. For simplicity's sake, let's set aside the fact that lumens are a poor measurement when it comes to plants/coral/etc. Let's also set aside the fact that not all of a bulb's light output goes into the tank, so all of these calculations are approximate. Say we have a light hood that puts out 100 lumens and we have a tank with a surface area of 1 square meter; that would be 100 lux. Now let's say we have a tank with a surface area of 1/2 square meters and a hood that fits that tank and puts out 100 lumens; that would be 200 lux. Your analogy assumes that we would use the same 1 sq.meter hood on the 1/2 sq.meter tank, in which case you are absolutely right that the lux would remain the same. Some of that light would be in the tank and some would be outside. Most people, however, use hoods that fit their tanks so most of the light goes in the tank, and therefore the size does change the lux.
What you're describing isn't lux per square inch, it's lumens per square inch. If you want to use square inches instead of square meters, that's fine, but it is not "lux" because "lux" is defined as lumens per square meter.
No, bulb manufactures cannot give a lux rating because lux depends on the surface area the light is shined at. They can ONLY give lumen ratings. The manufacturer only knows the amount of light that gets put out, not how that light is spread over your particular surface.
So, I'm chiming a bit late, and I don't have a whole lot to say, however I wanted to comment on the box inside a box thing.
This is from wikipedia and I think it will help you understand why the box inside a box model doesn't work. I recognize wikipedia isn't a credible source when it comes to legitimate research, but here on the internet it seems to pass the litmus test. That being said:
This is from wikipedia and I think it will help you understand why the box inside a box model doesn't work. I recognize wikipedia isn't a credible source when it comes to legitimate research, but here on the internet it seems to pass the litmus test. That being said:
Wikipedia "Lux" said:
I agree that it's a bad term and that logically it doesn't work. The point of this exercise is that I wanted to show that the term was the problem.
Jm I agree. The outside box is only 1 square meter though, so anything within that box (assuming no light escapes the 1 square meter box, would have the same lux.
However, as Cellodaisy said, if we can contain the same lumens within a smaller area than 1 square meter, the lux value has to go up. The same way as it goes down when you get outside the square meter area.
Jm I agree. The outside box is only 1 square meter though, so anything within that box (assuming no light escapes the 1 square meter box, would have the same lux.
However, as Cellodaisy said, if we can contain the same lumens within a smaller area than 1 square meter, the lux value has to go up. The same way as it goes down when you get outside the square meter area.
And Aye, there's the rub....
But if the light is focused on the inside box, despite being quoted for the large box, then it's lux will increase, not remain the same. Lux doesn't mean that the light puts out lumens in 1 square meter, it means if you measure the lumens on the surface of 1 square meter, it will be equal to that many lux. So if you measure those same lumens focused on a smaller area, the lux goes up.
Because we're dealing with glass boxes instead of solid boxes, it makes it difficult to say what the lux are. The best you can do is look at the lumen output of the light your working with, make the assumption that your reflectors reflect all light into your tank, and then compute the lux based on the surface area of your tank.
It's full of error, because A) not all lumens put out by the bulb make to the surface of the water B)even there, the light bends and reflects outside the glass, so it doesn't all remaine inside the "box".
Absolutely. Notice that 1 lux = 1 lumen per SQUARE meter not CUBIC meter, so when we're dealing with lux the strongest it will be is at the surface of our aquariums. Once it penetrates the water, there's a lot of other factors to deal with; turbidity and TDS in example.
