Naked Science Forum

General Science => General Science => Topic started by: neilep on 02/06/2017 11:37:17

Title: Does A Fully Mirrored Room Require Less Light To Light It?
Post by: neilep on 02/06/2017 11:37:17
Dearest Mirrorologists,

As a sheepy I of course love mirrors. Mirrors are my all time reflection glassy things that always look good when I stare into them ! ::)

Mirrors as ewe know were invented in 1983 by a lonely budgie who needed a chum**. Since then mirrors have been all the rage and still maintain their popularity to this day.

Look here I am in my mirrored room that was delivered last Tuesday.

 
* Screen Shot 2017-06-02 at 11.07.58.png (704.55 kB . 702x443 - viewed 5189 times)
True bona fide non doctored photo of me in my mirrored room literally just moments ago !

Nice eh ?

If all the mirrors in my room were absolutely perfect in ever possible way , would I be able to light the whole room with say....just one candle for instance ?  Would the light just keep reflecting ?   Could this save the worlds energy issues ? all we need do is dyson-sphere** the planet with a big mirror !!..sorted !!

Can I Light A Perfectly Mirrored Room With Just One Candle ? Does A Fully Mirrored  Room Require Less Light To Light It ?


whajafink ?

hugs and shmishes

mwah mwah

Sheepy xxxxxx



** Not true, it was 1985 !
**New verb ?
Title: Re: Does A Fully Mirrored Room Require Less Light To Light It?
Post by: David Cooper on 02/06/2017 16:48:34
White walls reflect most of the light that hits them too (they just scatter the light instead of reflecting it neatly), and while they absorb some of the light, so do mirrors, so I don't know if the room will be any brighter. You'd need to measure how much light is absorbed by different surfaces to find out.
Title: Re: Does A Fully Mirrored Room Require Less Light To Light It?
Post by: evan_au on 02/06/2017 23:44:48
If all the light from a candle were perfectly reflected from mirrors until it was absorbed by something...
- a rectangle-shaped room would not distribute the light very evenly, since most of the visible light would bounce of corner reflectors (which form every corner of the room), and end up getting absorbed by the candle flame and turned into invisible heat
- Much of the remainder would end up on an absorber (you)
- Only a small amount would end up on the book you are trying to read
- And only a small fraction of that would end up in your eyes.
- A candle is pretty pathetic for illumination

Now, if we were wearing a reflective spacesuit, and the book were printed on sheets of shiny aluminium foil, maybe....
Title: Re: Does A Fully Mirrored Room Require Less Light To Light It?
Post by: evan_au on 03/06/2017 07:28:13
Quote from: sheepish
A Fully Mirrored  Room
The ideal room to make best use of your 1 candlepower illumination would be a silvered ellipsoid, with the candle at one focus, and your book at  the other focus. This captues the maximum light from the candle and focuses it on the book.

The unfortunate reader would be huddled on the side of the book away from the candle.
Title: Re: Does A Fully Mirrored Room Require Less Light To Light It?
Post by: Colin2B on 03/06/2017 09:00:35

- ........and the book were printed on sheets of shiny aluminium foil, maybe....

I think sheepy uses vellum, although s/he should take care as it was often not calfskin 8)
Title: Re: Does A Fully Mirrored Room Require Less Light To Light It?
Post by: vhfpmr on 03/06/2017 11:35:42
Isn't it a matter of common experience that the paler the walls are decorated the brighter the room? Mirrors are just one step paler than white paint.

most of the visible light would bounce of corner reflectors (which form every corner of the room), and end up getting absorbed by the candle flame and turned into invisible heat
But a corner reflector returns a beam of light parallel to the incident beam, not convergent on the source.
Title: Re: Does A Fully Mirrored Room Require Less Light To Light It?
Post by: evan_au on 03/06/2017 12:49:20
Quote from: vhfpmr
But a corner reflector returns a beam of light parallel to the incident beam, not convergent on the source.
I agree - but then it will bounce off the diagonally opposite corner; won't this put it back on another parallel path, towards the candle flame?
Title: Re: Does A Fully Mirrored Room Require Less Light To Light It?
Post by: Bored chemist on 03/06/2017 13:05:27
The light would be bounced back to the flame- which it would be absorbed by.
This would heat the flame up, making it brighter.

The energy released from te burning wax has to go somewhere. If ewe discount the absorption into the book, mirrors and reader, then the only  "place" for that energy is as either radiation in the room, or as heat in the air in the room.
The longer the candle burns for, the brighter it gets.
Eventually, it will be bright enough to read.
Incidentally, re the "corner cube" effect- yes- but dfiraction...
Title: Re: Does A Fully Mirrored Room Require Less Light To Light It?
Post by: evan_au on 04/06/2017 00:29:17
Quote
This would heat the flame up, making it brighter.
An aside - is the light from a candle flame produced primarily through thermal effects, or through quantum effects?

If it is primarily black body radiation, then increased temperature will result in more radiation at visible wavelengths (and faster heating of the ambient air).
If it is primarily a quantum effect, then increased temperature won't significantly change the wavelength of the photons or the number of photons.
Title: Re: Does A Fully Mirrored Room Require Less Light To Light It?
Post by: Bored chemist on 04/06/2017 10:10:23
Quote
This would heat the flame up, making it brighter.
An aside - is the light from a candle flame produced primarily through thermal effects, or through quantum effects?

If it is primarily black body radiation, then increased temperature will result in more radiation at visible wavelengths (and faster heating of the ambient air).
If it is primarily a quantum effect, then increased temperature won't significantly change the wavelength of the photons or the number of photons.
The origins of quantum physics lie in the nature of the spectrum of black-body radiation. (The so called  "ultraviolet catastrophe")
They are two sides of the same coin.

Light from a candle is pretty close to black body radiation with a superimposed spectrum from things like CO, H2O and sometimes Na emissions.
Is that what you mean?

If the candle flame gets hotter it will get brighter.
The soot will give off more light and the spectrum will shift to the blue end .
Also, the proportion of light emitted by, for example, the blue CO lines will get brighter compared to the yellow Na lines.
Title: Re: Does A Fully Mirrored Room Require Less Light To Light It?
Post by: David Cooper on 04/06/2017 20:10:39
Quote from: vhfpmr
But a corner reflector returns a beam of light parallel to the incident beam, not convergent on the source.
I agree - but then it will bounce off the diagonally opposite corner; won't this put it back on another parallel path, towards the candle flame?

Only light that hits the very centre of the corner is returned to the same point of the source. The further away from the centre of the corner the light hits, the greater the distance by which it will miss the source on return.

Most of the light will hit mirrors far from the corners too, and some of it will zigzag from one side of the room to the opposite sides thousands of times before it reaches an end wall. However, mirrors can absorb a lot of light - I have a Pentax 500mm mirror telephoto lens (designed primarily to be used as a telescope) which is officially f/8, but the light meter shows it to be effectively closer to f/11 because so much light is absorbed by the two mirrors. It wouldn't surprise me if some white surfaces reflect more light than mirrors.
Title: Re: Does A Fully Mirrored Room Require Less Light To Light It?
Post by: vhfpmr on 18/06/2017 17:21:02
Quote from: vhfpmr
But a corner reflector returns a beam of light parallel to the incident beam, not convergent on the source.
I agree - but then it will bounce off the diagonally opposite corner; won't this put it back on another parallel path, towards the candle flame?
A couple of years ago m neighbour knocked on the door and pointed out that the front garden wall was a few inches over his side of the boundary. I forget how much, but the angle it made with the front of the house was about one degree off the normal. I told him that that's where it had been since the house was built, but he was still suspicious. He went quiet when I showed him that the rooms of the houses were even more off square though. I suppose if the mirrors are perfect, the light would keep going round until it found its way back to the flame eventually in any shape room though..........