Does ceiling bouncing reduce lumens?

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Bort
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Does ceiling bouncing reduce lumens?

I swear that when i bounce 1600 lumens off a ceiling it does not light up the room even close to a 1600 lumen light bulb.
Some of it is light direction of course but it seems the ceiling is eating a fair number of lumens.

Anyone have testing data they can share or thoughts?

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MoreHiCRILumens
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Unless ceiling is a mirror there will probably be some losses. Not like mirror is either 100% reflective. So I think yes.

Data would be better.

richbuff
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Is it a small white room? That works best for me.

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Oli
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If you put a lamp shade, even a mirrored shade on your other 1600 lumen bulb and bounced that light off of the ceiling the flashlight would probably do better than the bulb assuming you’re illuminating roughly the same amount of ceiling. Your flashlight reflector would be better suited at directing light than your mirrored lamp shade would be.

You can't compare the big flashlight in the sky to the little flashlight in your hand.

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not really, any plain white ceiling is going to bounce 95-99% of the light coming at it

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Oli
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wle wrote:
not really, any plain white ceiling is going to bounce 95-99% of the light coming at it
In what direction? Also too much unknown about the other bulb such as location and whether or not it has a shade or housing or other. Color? Too many unknowns. Mirrored shade, same location, same area of ceiling illuminated the flashlight would do better, probably indistinguishable.

You can't compare the big flashlight in the sky to the little flashlight in your hand.

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The highest reflectivity of standard white paint is about 93% (and that’s for glaringly pure ultrawhite that most folks wouldn’t use for an interior paint). Most white walls and ceilings probably have a diffuse reflectance of less than 90%.

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Answer: yes.

How much: depends.

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OldLaserGuy wrote:
The highest reflectivity of standard white paint is about 93% (and that’s for glaringly pure ultrawhite that most folks wouldn’t use for an interior paint). Most white walls and ceilings probably have a diffuse reflectance of less than 90%.

Interesting, where are these numbers from?

The Journal of Alternative Facts TM

"It is critical that there is a credible academic source for the growing and important discipline of alternative facts. This field of study will just keep winning, and we knew that all the best people would want to be on board. There is a real risk in the world today that people might be getting their information about science from actual scientists"

 

 

 

chadvone
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Bort wrote:
OldLaserGuy wrote:
The highest reflectivity of standard white paint is about 93% (and that’s for glaringly pure ultrawhite that most folks wouldn’t use for an interior paint). Most white walls and ceilings probably have a diffuse reflectance of less than 90%.
Interesting, where are these numbers from?

Post 7

Big Smile
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chadvone wrote:
Bort wrote:
OldLaserGuy wrote:
The highest reflectivity of standard white paint is about 93% (and that’s for glaringly pure ultrawhite that most folks wouldn’t use for an interior paint). Most white walls and ceilings probably have a diffuse reflectance of less than 90%.
Interesting, where are these numbers from?

Post 7

Big Smile
Since i quoted post 7 that is self evident Steve

The Journal of Alternative Facts TM

"It is critical that there is a credible academic source for the growing and important discipline of alternative facts. This field of study will just keep winning, and we knew that all the best people would want to be on board. There is a real risk in the world today that people might be getting their information about science from actual scientists"

 

 

 

OldLaserGuy
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Bort wrote:
OldLaserGuy wrote:
The highest reflectivity of standard white paint is about 93% (and that’s for glaringly pure ultrawhite that most folks wouldn’t use for an interior paint). Most white walls and ceilings probably have a diffuse reflectance of less than 90%.
Interesting, where are these numbers from?

https://www.kylieminteriors.ca/paint-colour-review-the-5-whitest-white-p...

It turns out my recollection was off by 1%. Behr Ultrawhite actually has a reflectance of 94% not 93. Thanks for keeping me honest. This was the paint I found to coat the inside of my styrofoam integrating sphere (similar to many of the ones built by folks on this forum). To get any better than this you have to start playing with BaSO4 preparations (not in any common household paint). The best of these will get you around 97% reflectance if you do everything perfectly, but are easy to get wrong – and are quite expensive (several hundred dollars for enough to coat a 1 foot sphere).

My claim that most interior wall paints have a reflectance under 90% is more anecdotal. When my wife and I redecorated we were looking for a white “clinical” look for the kitchen. We were steered strongly away from the pure whites and told that most interior white paint was off white to some degree. Since pure white interior paint is typically in the 92-94% reflectance range, I guesstimated that typical off-whites would be less than 90.

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OldLaserGuy wrote:
We were steered strongly away from the pure whites and told that most interior white paint was off white to some degree.

Yeh, most interior “white” paint is actually a softer off-white, whether “bone”, “cameo”, “pearl”, other fancy names for ‘em.

Same with cars. My LaCrosse is (to me) a beautiful white. Looks bright, but… It’s called “White Diamond Pearl” (toldja, fancy names). Anyone walking up to it knows it’s… well… white, not “off-white”, ie, it’s not noticeably “off”.

Yet my neighbor’s white soov (huge Nissan, I think) is this stark harsh blindingly-bright white. I mean a harsh scorching retina-searing pain-inducing white. I never really noticed ‘til I actually compared the two almost side-by-side. And then the difference was painfully apparent.

And yeah, same with interior paints. “Bone” is more of a grayish white, “pearl” a slightly warmer if not rosier shade, etc., but they also color the reflected light somewhat.

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wle wrote:
not really, any plain white ceiling is going to bounce 95-99% of the light coming at it

That’s actually in the realm of laboratory physics experiments. The highest reflection achieved so far is 98.1%:

https://www.purdue.edu/newsroom/releases/2021/Q2/the-whitest-paint-is-he...

Fresh snow is a very highly reflective natural example and is around 90%.

I don’t have good information on conventional paints, and some of the data I see when I search appears to have not been taking on accurately calibrated instruments. However, as I understand it, most white paints fall into the 80-90% reflectance range when new, and of course, they’ll fade some over time. I would not be the least bit surprised if some of the further off-whites are below 70%.

I actually was surprised when I bought an 18% reflectance grey card for photography, just how light even a surface that absorbs 82% of the light falling on it looks.

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In summary, yes ceiling bouncing reduces lumens. A bulb that shines light directly will provide slightly more illumination. It also will feel brighter if the source is visible the eyes.

Lastly, distribution matters. Putting a small spot in one location on the ceiling is not going to distribute that light around the room well. Lack of illumination along the walls in particular can make a room feel dark. In high end architecture, you may notice that the lighting designer often places downward shining lights close to the walls to “wash” them in light.

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Took me a while to get back to this thread, my bad.

Lots of interesting replies, 94% is quite good.
The not pure white comments are puzzling, are most people not using pure white for ceilings?

The Journal of Alternative Facts TM

"It is critical that there is a credible academic source for the growing and important discipline of alternative facts. This field of study will just keep winning, and we knew that all the best people would want to be on board. There is a real risk in the world today that people might be getting their information about science from actual scientists"

 

 

 

Bort
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OldLaserGuy wrote:
Bort wrote:
OldLaserGuy wrote:
The highest reflectivity of standard white paint is about 93% (and that’s for glaringly pure ultrawhite that most folks wouldn’t use for an interior paint). Most white walls and ceilings probably have a diffuse reflectance of less than 90%.
Interesting, where are these numbers from?

https://www.kylieminteriors.ca/paint-colour-review-the-5-whitest-white-p...


That is a most interesting link.
Now i will have to ensure all paint i buy has the highest LRV!

The Journal of Alternative Facts TM

"It is critical that there is a credible academic source for the growing and important discipline of alternative facts. This field of study will just keep winning, and we knew that all the best people would want to be on board. There is a real risk in the world today that people might be getting their information about science from actual scientists"

 

 

 

Lightbringer
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Bort wrote:
The not pure white comments are puzzling, are most people not using pure white for ceilings?

Quite rare, actually.

It was more common in old old old buildings where the ceilings were never repainted, but in more modern times, like after electricity was invented, off-white became the norm.

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Lightbringer wrote:
Bort wrote:
The not pure white comments are puzzling, are most people not using pure white for ceilings?

Quite rare, actually.

It was more common in old old old buildings where the ceilings were never repainted, but in more modern times, like after electricity was invented, off-white became the norm.


Interesting
So if i have off white i might be losing maybe 15-20% of ceiling bounced lumens

The Journal of Alternative Facts TM

"It is critical that there is a credible academic source for the growing and important discipline of alternative facts. This field of study will just keep winning, and we knew that all the best people would want to be on board. There is a real risk in the world today that people might be getting their information about science from actual scientists"

 

 

 

Lightbringer
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Bort wrote:
Lightbringer wrote:
Bort wrote:
The not pure white comments are puzzling, are most people not using pure white for ceilings?

Quite rare, actually.

It was more common in old old old buildings where the ceilings were never repainted, but in more modern times, like after electricity was invented, off-white became the norm.


Interesting
So if i have off white i might be losing maybe 15-20% of ceiling bounced lumens

Probably. No worse than diffuser caps people use to turn flashlights into lanterns, though.

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