What Is a Spectrophotometer and What Does It Do?

Spectrophotometers are fine.

But they will never convince a determined woman that that discoloration in the hallway is a shadow.

Never mind that it wasn't there all the time.

God love 'em!

Tell him, for me, that he better have that paint color matched and on hand for touch-ups.

Some things are better left alone. If women think they can discern these color subtleties and it keeps us from re-painting, I say let them.

Well thats what he did in the end. Two separate cans each labeled for the different paint color but inside they are both the exact same paint mix he blended together from the originals himself.

Personally between you and me being I have been married two years now I too have a few little secrets like this already that in a sick sort of way give me satisfaction justification to feel that my wife is nuts as well.

They make her happy and I get to grin for my own reasons as well.

Two years?

You aren't even really MARRIED yet if it's only been two years.

I've got over 20 years with two different women. Not at the same time, either.

I still don't get it.

Heck... 32 years here with the same one and some things are still a mystery. And you know what... I hope it stays that way. Keeps things interesting if you ask me.

That's a good story!

The actual reflected color is a combination of the paint color and the illumination color, which is why colors sometimes look different under fluorescent lighting. I can imagine that the light illuminating the ceiling might be a slightly different color from that hitting the walls since the ceiling is facing the floor. The eye does a good but not perfect job of cancelling out the effect of illumination. It might be interesting to take a photograph and see how the colors compare.

Rixter: "The actual reflected color is a combination of the paint color and the illumination color"

You got it right. Reflected color is a processed color and its intensity down and once again when reflected by another surface causes a shadow or even difference in color as reflection is not in same proportion for all colors or Photon Energies (which is what we call color E = hv) and sometime also expressed in wavelength in nm. Color is defined for a white light source of all energies / wavelengths (nearly) uniformly present.

Well, since the stuff in the can is still wet it wouldn't look like the same shade, so how can they be so sure?

Lol, yes. But if you have a spectrophotometer you can make a stronger case. Not that it will help the marriage...

From my experience in the medical device industry, a spectrophotometer can only tell the denstity of, in this case, paint - send light through a clear medium then send the light through the sample (paint) then calculate the difference. This is done with human blood to figure the hemoglobin (iron) in the patient sample.

Chemistry systems can look at different wavelengths, again the light must shine through the sample.

I fear with the paint, it may be too dense for the light to shine through. I know of several local paint shops that claim "we will match your paint color". Maybe if your purchased paint was not a good match, you might want to find another paint professional to match your mustard!

Hemoglobin is determined by transmission spectroscopy, whereas, paint samples are measured by reflectance spectroscopy. In reflectance spectroscopy, the opaque sample is illuminated by a white light and the reflected light is analyzed for its spectral content using a pure white sample as a blank (baseline).

Interesting article.

Spectrophotometers have lots of other uses. As it turns out, aviation people are rather particular about cockpit lighting. They like to have the EXACT shade of red, green, blue, pink, yellow, orange, white, (even black) on all their cockpit displays. It can be a tough job to get them to match, especially when a particular LCD goes obsolete, and you've got to try to match the lighting using multiple sources of LCDs and LEDs.

Oh, and compatibility with night vision goggles, too? So no real deep reds, only orangy-reds. Right, got it.

Yeah, spectrophotometers (aka, spectroradiometers) can be pretty useful.

Not just that. I've since learned that the same technology, albeit with a much wider sample of wavelengths, is used to determine the chemical composition of stars. Kind of makes me wish I'd studied physics.

No one can see colours just the reflection, now just what is causing the light that allows a reflection? Direct sunlight, indirect sunlight, reflection off of close by objects. Mix all you want but be aware of the variations caused by the lighting source or sources.

With regards to the lady in your life when building our last house I was using a 4 ft. level to hang the cupboards and my dear wife stood back and claimed that the level was incorrect. We never did settle that incident to her satisfaction.

If your house is anything like my 1973 vintage track development slapped together house, there is a saying in the neighborhood that nothing is flat, level, square, plumb or straight.

Therefore, even if your cupboard is hanging such that it is perfectly level, nothing else is level and therefore "looks" wrong??

Of course those living in much older homes often have floors that shed water quite nicely. We used to be able race matchbox cars on the kitchen floor where I grew up.

The 150 year old farmhouse I was raised in was similar, Dining room to living room had a slope that toy cars would coast down. Dad jacked the house as much as possible to straighten it then installed hydronic heating on the floor and leveled as much as possible with concrete. Nice job and warm to play on.

Every time I walk into a factory built house the squareness is evident compared to a normal built on site structure. They may be quite close but to my eye the exactness of the factory homes stands out.

We have been through similar issues with dad when it came to replacing old walls and windows in some of our old farm buildings.

He likes to make everything perfectly straight and level which is fine except when you do it in a crooked building. The new part just never looks right or like it belongs there afterwards.

Then on the other hand I have friends of mine who added a boiler room to their shop some years ago and built it crooked mostly because they were in too big of hurry to ever measure anything.

Adding a crooked addition to a crooked building should fit just fine of course unless you get your crooked directions wrong then it just makes the new part look even worse.

THIS. How many pictures have I checked in the upstairs office of our ~90 year old home to find that they are on-bubble, and the ceiling or nearest corner is not.

Double sticky back foam tape?