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what's a lux?

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    Posted: December 05 2005 at 1:10am
Is there anyone out there that can explain to me what a lux is?  It's not the same as Kelvin, is it?

Edited by Amie - January 10 2008 at 3:00am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Adam Haycock Quote  Post ReplyReply Direct Link To This Post Posted: December 05 2005 at 1:35am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mark Peterson Quote  Post ReplyReply Direct Link To This Post Posted: December 05 2005 at 8:48am

This is a very important topic and it should be moved to the Lighting section.

We also need to discuss Lumens and Color Rendering Index (CRI)

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Post Options Post Options   Thanks (0) Thanks(0)   Quote jfinch Quote  Post ReplyReply Direct Link To This Post Posted: December 05 2005 at 9:06am

And most importantly... PAR.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Guests Quote  Post ReplyReply Direct Link To This Post Posted: December 05 2005 at 9:25am
Originally posted by Mark Peterson Mark Peterson wrote:

This is a very important topic and it should be moved to the Lighting section.

We also need to discuss Lumens and Color Rendering Index (CRI)

I knew someone was going to say that.  I put it in this section because I am trying to build something that is not fish related.  I am trying to design a light box for someone that has Seasonal Affected Disorder (SAD).  The person is suppose to sit 20" away from lights that are 10,000 lux for 20 minutes a day.  Is there someway to measure the lux of a light at a given distance? 

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Adam Blundell Quote  Post ReplyReply Direct Link To This Post Posted: December 05 2005 at 9:32am

Amie-
I have a lux meter you can borrow.  Let me find it....

Adam

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Post Options Post Options   Thanks (0) Thanks(0)   Quote jfinch Quote  Post ReplyReply Direct Link To This Post Posted: December 05 2005 at 9:33am

Is there someway to measure the lux of a light at a given distance?

Yes.  Get or borrow a lux meter (photographers use them).  A 250 W MH bulb has an intensity of about 24,000 lumen.  Spread all that light out over 2 meters and you would have 12,000 lux.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Guests Quote  Post ReplyReply Direct Link To This Post Posted: December 05 2005 at 9:48am
Originally posted by Adam Blundell Adam Blundell wrote:

Amie-
I have a lux meter you can borrow.  Let me find it....

Adam

Fantastic!  Thanks.

Originally posted by JFinch JFinch wrote:

Amie-A 250 W MH bulb has an intensity of about 24,000 lumen.  Spread all that light out over 2 meters and you would have 12,000 lux.

Sounds like a good reason to get a MH on my tank.    Seriously though, is there a distance that you could sit from your tank and the lux would be 10,000?  I guess the hood of the tank would have to be up, right?   Would a 125 W MH mean that you would only have to be 1 meter away to get 11,000 lux?



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Post Options Post Options   Thanks (0) Thanks(0)   Quote Adam Haycock Quote  Post ReplyReply Direct Link To This Post Posted: December 05 2005 at 3:26pm

Amie, does it say anything about what color of light to use? Id would think a 6500K metal halide would be perfect for that. Hmm maybe a good excuse to buy a pendant for a new frag tank ;)

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Post Options Post Options   Thanks (0) Thanks(0)   Quote bbeck4x4 Quote  Post ReplyReply Direct Link To This Post Posted: December 05 2005 at 10:27pm
we have a box that is supposed to be used for SAD it has two 65 watt f40bx/spx41/rs bulbs in it, that would be a 4100 k bulbs

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Guests Quote  Post ReplyReply Direct Link To This Post Posted: December 06 2005 at 12:46am
Originally posted by Adam Haycock Adam Haycock wrote:

Amie, does it say anything about what color of light to use? Id would think a 6500K metal halide would be perfect for that. Hmm maybe a good excuse to buy a pendant for a new frag tank ;)

The only information I have been able to find states that the light needs to be 10,000 lux at 12", properly screen out UV wavelengths, and preferably have  a broad spectrum of color.  ( I guess the color doesn't matter as much.)  I think the idea is to simulate sunlight. 

Is a 6500 K light 'whiter' or more yellow than a 10,000 K light?

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Post Options Post Options   Thanks (0) Thanks(0)   Quote faviasteve Quote  Post ReplyReply Direct Link To This Post Posted: December 06 2005 at 1:10am
6500 K is more yellow than 10,000K so it isn't as pretty on a reef tank but the the Iwasaki 6500 K simutates natural sunlight at the surface better than any other metal halide so it should be a super SAD bulb.  Anything between 4000 K and 10000 K is probably OK.
Steve Burton

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Guests Quote  Post ReplyReply Direct Link To This Post Posted: December 06 2005 at 11:40am

Originally posted by bbeck4x4 bbeck4x4 wrote:

we have a box that is supposed to be used for SAD it has two 65 watt f40bx/spx41/rs bulbs in it, that would be a 4100 k bulbs

Brian

Are you using it?  Do you want to sell it?

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Post Options Post Options   Thanks (0) Thanks(0)   Quote bbeck4x4 Quote  Post ReplyReply Direct Link To This Post Posted: December 06 2005 at 6:18pm
we are using it with a timer to have the daylight (simulated) occur at 6:00 am, so far its working pretty good, I was having trouble with staying asleep at night.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Guests Quote  Post ReplyReply Direct Link To This Post Posted: December 12 2005 at 11:16am
Thanks to Adam letting me borrow his lux meter, I was able to test different lights.  I found that a 55 Watt 10,000K power compact emits 10000 lux at 20 inches.  Now I just need to figure out the UV issues and I'm set.  I assume that I can just get a piece of UV protective glass from a glass company?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Adam Blundell Quote  Post ReplyReply Direct Link To This Post Posted: December 12 2005 at 11:19am

Yes, but I would get a piece wide enough to cover two bulbs.  After using that glass you will lose a lot of your light and may need to use two 55 watt bulbs.

JON- do you think you need to filter UV light from pc bulbs?  I don't.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote jfinch Quote  Post ReplyReply Direct Link To This Post Posted: December 12 2005 at 11:35am

do you think you need to filter UV light from pc bulbs?  I don't.

I doubt it too.  I'd use the bulbs as is.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Guests Quote  Post ReplyReply Direct Link To This Post Posted: December 12 2005 at 11:38am
Originally posted by Adam Blundell Adam Blundell wrote:

JON- do you think you need to filter UV light from pc bulbs?  I don't.

Adam

You are right, Adam... I went back and reread the article you sent me on UV Radiation (http://www.advancedaquarist.com/issues/aug2004/feature.htm) and I don't need to worry about Power Compacts unless the total wattage is above 400.

Thanks for ALL your help!

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