Electrical Equations

[Post=79734 ChrisGreaves]

I replaced two burned-out Halogen lights from a bathroom fitting with the recommended set "G9 20W" bulbs, each bulb about the size of two finger knuckles.
The bathroom sink now has 3x20W globes burning in the clear, that is, no enclosing shades.
I remember the business of adding resistances for DC electrical power - the reciprocal of the sum of the reciprocals - and seem to recall a similar convolution for wattage, or better still, luminosity.

Simple question: If I'd installed 3x40W bulbs instead of 3x20W bulbs, would the room be twice as bright?

[HansV]

Not to the human eye - while luminosity is simply additive, our perception of brightness works on a logarithmic scale. Twice the light "output" results in only about 30% increase in perceived brightness.

[Post=79744 viking33]

Chris, Are you confusing AC power with DC power?
From a Boston University physics web site is a nice little primer on the two.

http://physics.bu.edu/~duffy/PY106/Resistance.html

[Post=79745 BobH]

I belong to an organization called Dark Skies. We take a position against light pollution that the night skies across the world are subjected to.

It is a shame that communities cannot be convinced that adding light does little good. There are peer-reviewed, replicated studies that show that increasing public lighting does NOT deter crime and that reducing public lighting does NOT increase it.

[Post=79746 viking33]

I belong to an organization called Dark Skies. We take a position against light pollution that the night skies across the world are subjected to.

It is a shame that communities cannot be convinced that adding light does little good. There are peer-reviewed, replicated studies that show that increasing public lighting does NOT deter crime and that reducing public lighting does NOT increase it.

Boy, do I agree with that position!!!!
Super market parking lot lights on all night and pointed UP at the sky.
Halogen & Sodium street lights on every other pole and still people drive with high beams on. Look at a picture of ANY city at night with huge buildings lit up like Christmas trees with practically no one in them. Etc, etc.
I never heard of Dark Skies. Is it a local organization?
I'll have to Google them to read more.

[Post=79747 BobH]

Here you go!

http://www.darksky.org/

[Post=79751 AlanMiller]

Chris, Are you confusing AC power with DC power?

Hi Bob!

Not sure what an AC or DC source has to do with power through a purely resistive circuit.
Or am I missing some context here?

Alan

[Post=80140 ChrisGreaves]

Not to the human eye - while luminosity is simply additive, our perception of brightness works on a logarithmic scale. Twice the light "output" results in only about 30% increase in perceived brightness.

Thanks Hans. I had a sneaking suspicion of that; faint memories of Mr Puzey's physics class of 1963.