Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: John Chapman on 15/02/2009 19:04:29

Title: If you open the door on a well lit room does the room become darker?
Post by: John Chapman on 15/02/2009 19:04:29

Imagine you are pottering around in your garden shed at night. The shed has no windows and is illuminated within by a bright light. The door is closed and fits so well that, from outside, there is no light escaping. Suddenly you open the door and a shaft of light is projected the length of your garden.

My question is this:

Since the amount of light being produced by the bulb is the same whether the door is open or closed and, since with the door open some of that light is escaping, does the inside of the shed become darker (or at least less light) when the door is open?


I'm pretty sure I know the answer to this question, which seems fairly obvious to me, but when I put it to the guys at work they all disagreed. So I'm now depending on you all to settle a wager for me which is worth a chicken curry if I win. More importantly it's also worth a chicken curry if I lose! I love curries so please don't let me down.

Title: If you open the door on a well lit room does the room become darker?
Post by: lyner on 15/02/2009 19:09:12

If you took all the walls away and the ceiling and, if it were pitch black outside, then it would get a lot darker - only light direct from the lamp would reach objects and nothing from the walls.
So, taking a piece of reflective wall away will have a small effect of darkening the room. You are probably right(?).

Title: If you open the door on a well lit room does the room become darker?
Post by: John Chapman on 15/02/2009 19:14:14

Thanks for that sophiecentaur

I'm not allowed to say yet what my opinion is or the guys at work will say I've lead you on! But, actually it was neither a simple 'yes' or 'no'. Any other opinions, anyone?

Title: If you open the door on a well lit room does the room become darker?
Post by: Bored chemist on 15/02/2009 19:39:28

If the door were matt black then opening it might make the room slightly lighter. Some light might get scattered back in by whatever is outside.
Imagine you are in the room with the blacjk door and someone opens it. What was a black rectangle is no a dimly lit garden - that's slightly brighter. More light reacxes your eyes and so more light must be present in the room.

Title: If you open the door on a well lit room does the room become darker?
Post by: John Chapman on 15/02/2009 20:15:51

Hi Bored Chemist

That's more or less exactly the answer I gave to my work colleagues. I said I believe it is dependent on the brightness of the door. If the door is brighter than outside, the shed will become dimmer. If it is darker the shed will become lighter.

My work mate has a theory to do with the fact that a door of a particular colour can only reflect a small part of the light spectrum (unless that colour is white, of course). But I think that is largely irrelevant.

Does anyone else have any impute?

Title: If you open the door on a well lit room does the room become darker?
Post by: lyner on 15/02/2009 20:56:25

impute?
A Freudian slip if ever there was one!
 [:)]

Title: If you open the door on a well lit room does the room become darker?
Post by: John Chapman on 15/02/2009 21:28:56

Ha ha

I originally wrote "imput" and the spell checker picked it up and made several suggestions. I must have clicked on the wrong one.

You see I have spent all evening staring into a torch, firstly to create dark blotches in my vision and secondly to try and make myself sneeze. This was for two other threads on this site:

blotches:  http://www.thenakedscientists.com/forum/index.php?topic=20154.0;topicseen

sneezing:  http://www.thenakedscientists.com/forum/index.php?topic=20405.0;topicseen

The problem is that now, except for the blotches, I can't see a bleedin' thing!






atishoo!

Title: If you open the door on a well lit room does the room become darker?
Post by: Chemistry4me on 16/02/2009 04:12:26

All in the name of science!