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I just wanted to comment on something that i have noticed happen in my tanks and i'm sure happens to everybody. It's more of a psychological thing than a physical thing with the tanks. As i have gone through the years, i have upgraded my lighting many times over my 29g tank. The first was an upgrade from a 20w 2500k bulb to a 20w 6500k bulb, and i immediately noticed the difference. However, after a while, it seemed as though the new bulb was getting dim, to the point that it was similar in color to the 2500k (this wasn't because the bulb was old, though). I then upgraded to 65w, and i thought that my fish were gonna get sunburn, since it was so bright. However over time, i have gotten used to the 65w 6500k light, and now mentally think it looks not much brighter than my original 20w 2500k bulb did. Obviously that's not true, so that's what i refer to as the darkening effect. Do y'all have a similar thing happen to you?
 

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Part of it may just be the gradual loss of light intensity as the bulb ages. How old were they? You can't really say for sure unless you have a new, but otherwise identical, bulb to compare with.


The same thing happens with fish tanks though. My 75 used to be big.
 

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i was contemplating this today. i used to think my 29g was pretty bright with the 2 24w t5ho bulbs. now that i've set up my 50g low tech with 2 21w t5no bulbs it just doesn't look as bright. i chalked it up to the to fact that the 50 is acrylic and just looks brighter.

it's probably all in our heads... idk
 

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PC bulbs lose a lot of intensity in the first 2 months or less, then they settle down to hold that intensity for about 18 months to 2 years. It could be that initial loss of intensity, combined with the fact that our eyes tend to make everything look like our subconscious thinks they should. So, all light looks about the same brightness over time. (My experience, anyway.)
 

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PC bulbs lose a lot of intensity in the first 2 months or less, then they settle down to hold that intensity for about 18 months to 2 years. It could be that initial loss of intensity, combined with the fact that our eyes tend to make everything look like our subconscious thinks they should. So, all light looks about the same brightness over time. (My experience, anyway.)
Really, I've never heard that before.
Where did you get that information?
 

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Our perception of light and the actual amount present are two different things. Our brains/eyes can adjust to dim lighting conditions as well as very bright conditions. We "gain up" or "gain down" just like a camera. To see what I mean shoot some photos with a camera using manual settings with no flash. Can't site any science just personal experience shooting tv commercials and photography.
 

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^ Put it this way: your pupil is like the aperture of a camera, and your iris is like the aperture control mechanism (what's that called on a camera? the aperture stop?).

Yes, I believe it is more a testament to the powers of optics and the human brain then a quantifiable decrease in light. Of course, if you're talking about bulbs that are very old, then, well, it's probably just time to change out the bulbs!
 

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Really, I've never heard that before.
Where did you get that information?
If you mean about the loss of intensity for PC bulbs, I got the data from someone on one of these forums, who had a PAR meter available, and a lot of PC bulbs of various ages to test.


You can see that the bulbs dropped from around 1900 to around 1350 in about 3 months or less.

If you meant the part about how your eyes/brain adjust light to look like it "should look", I first learned about this from inadvertent experiments. Many years ago, when I used to hike a lot, I was in a National Park, somewhere, way out on a trail, and had reason to use one of the PortaPotties left there. It had a dark green plastic roof. When I entered, the inside was an eerie green color - everything looked green from the green light filtering in through the roof. By the time I left, I didn't notice the green, which amused me, but when I got outdoors, everything was a purple red color, and I mean everything. Shortly after, the colors were normal again.

Years later I put GE9325K bulbs on my tank - instant lavender pink tank. But a few days later the tank looked perfectly normal, unless I looked out the window for awhile, then looked back at the tank. Or, if I took a photo of the tank, the tank color was back to the lavender-purple color. All of this was just my brain/eyes adjusting the colors to fit what my subconscious knew they should be. Remember, color as we perceive it is a totally artificial thing. It is just an interpretation of the various light wave lengths we see. Look at a NASA artificial color photo of Mars, for example to see what happens if you assign red to infrared, blue to far ultraviolet, and green to some longer wave length ultra violet. You get a perfectly "normal" photo, but the colors are artificial, as all colors are.
 

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^ Put it this way: your pupil is like the aperture of a camera, and your iris is like the aperture control mechanism (what's that called on a camera? the aperture stop?).

Yes, I believe it is more a testament to the powers of optics and the human brain then a quantifiable decrease in light. Of course, if you're talking about bulbs that are very old, then, well, it's probably just time to change out the bulbs!
Actually, I'd compare it to the gain function in a video camera-sensitivity to light-iris is the controller of how much light does or doesn't reach the "sensitized" or "de-sensitized" optic nerve. As Hoppy points out our brain can adjust the perception of the color of light. Our brain does an automatic white balance for us.
 

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Our brain does an automatic white balance for us.
That is it exactly! And, if you suddenly change the ambient light - walk out of a trailside portapotty, after studying your trail map in there, your white balance no longer matches the light and everything looks very, very weird for a few minutes.
 
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