# Physics of light: what is brightness? **URL:** \ **Category:** Factual Questions\ **Created:** [December 20, 2004, 9:54pm UTC](https://boards.straightdope.com/t/physics-of-light-what-is-brightness/280868 "2004-12-20T21:54:02Z")\ **Posts on this page:** 6\ **Page:** 2
**Author:** ![Telemark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/telemark/32/372_2.png) [@Telemark](https://boards.straightdope.com/u/Telemark)\ **Post date:** [March 30, 2016, 3:14pm UTC](https://boards.straightdope.com/t/physics-of-light-what-is-brightness/280868/21 "2016-03-30T15:14:13Z")
> [@CalMeacham](#): > > Boy, are you opening a can of worms. I say that as an Optics guy. Note that this particular can has been open for 12 years. ---
**Author:** ![running\_coach](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/running_coach/32/15836_2.png) [@running\_coach](https://boards.straightdope.com/u/running_coach)\ **Post date:** [March 30, 2016, 3:18pm UTC](https://boards.straightdope.com/t/physics-of-light-what-is-brightness/280868/22 "2016-03-30T15:18:18Z")
> [@John\_Mace](#): > > The “can of worms” was opened 12 years ago, FYI, in case you didn’t notice… And to think he’s an Optics guy. ---
**Author:** ![watchwolf49](https://avatars.discourse-cdn.com/v4/letter/w/e9c0ed/32.png) [@watchwolf49](https://boards.straightdope.com/u/watchwolf49)\ **Post date:** [March 30, 2016, 3:44pm UTC](https://boards.straightdope.com/t/physics-of-light-what-is-brightness/280868/23 "2016-03-30T15:44:48Z")
Power = ∫ Intensity dot the differential of Area. Sounds like intensity is much the same as flux, as both are vector values. ---
**Author:** ![CalMeacham](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/calmeacham/32/35_2.png) [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)\ **Post date:** [March 30, 2016, 4:52pm UTC](https://boards.straightdope.com/t/physics-of-light-what-is-brightness/280868/24 "2016-03-30T16:52:26Z")
> [@John\_Mace](#): > > The “can of worms” was opened 12 years ago, FYI, in case you didn’t notice… I noticed. But it came up here, so I answered it. I missed it the first time it appeared, or I would’ve answered it then. ---
**Author:** ![Senegoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/senegoid/32/6606_2.png) [@Senegoid](https://boards.straightdope.com/u/Senegoid)\ **Post date:** [March 30, 2016, 10:12pm UTC](https://boards.straightdope.com/t/physics-of-light-what-is-brightness/280868/25 "2016-03-30T22:12:03Z")
> [@CalMeacham](#): > > I noticed. But it came up here, so I answered it. I missed it the first time it appeared, or I would’ve answered it then. This thread may have been originally started 12 light-years away from here, so that’s why you’re just seeing it now. ---
**Author:** ![Isilder](https://avatars.discourse-cdn.com/v4/letter/i/cc9497/32.png) [@Isilder](https://boards.straightdope.com/u/Isilder)\ **Post date:** [March 31, 2016, 12:25am UTC](https://boards.straightdope.com/t/physics-of-light-what-is-brightness/280868/26 "2016-03-31T00:25:08Z")
Well all this discussion about measuring, its not clear if the photon is a real thing, or just a metaphore for amplitude… Double slit experiment… since the photon can go through both slits at once, it stands to reason that if two do that at the same time, its really doubling the amplitude of the energy going through the slits… The idea is that the energy can only transfer to the detectors when the detectors quantum rules are obeyed… since the detector is like an electron jumping shell in a phosphorous atom, its possible to say its a single photon THERE and THEN… Not before. That is why its said to be a particle, really EM is a quantum field, which is not the same as a wave and not the same as a particle. But for metaphoric purposes, the quantum field can be c compared to a wave… and only then forced into being a particle at the interaction with the electron ( or positron,etc, but thats rather theory or academic … not what we have light doing here…)… This is what the double slit experiment shows… its certainly not acting like a particle when it goes through those slits ! [Previous page](https://boards.straightdope.com/t/physics-of-light-what-is-brightness/280868.md?page=1)