Reddit reviews Introduction to Radiometry and Photometry

Hmmm.....

>why would anyone use mirrors when the cost of a roll of quality foil is only a few bucks and can be cut to size?

A mirror was likely not used, Mylar was. You can see in certain areas where the Mylar was not flat causing distortions. Either that or a first surface mirror like material that behaves like Mylar. Optically they would behave the same. The OP never actually stated what the material was.

>Depending on the intensity of the light, using shitty mirrors has a high chance to cause light issues.

Prove it- the burden of proof is on you as the person making the claim. I've done a lot of testing and have never seen light burn from any mirror or mirror like material with indoor grow lighting levels.

>The issues that foil could cause all stem from shitty application and carelessness of installation. If you keep your foil smooth and unwrinkled, you'll have zero chance of light issues.

I used wrinkled and non-smooth foil in my lighting guide to demonstrate that at half full sunlight intensities plants were not burning. Due to non-photochemical quenching alone one should not go past these lighting levels which is about 1000uMol/m2/sec. I even formed concave structures to try to burn plants. It never happened. In this case a quantum light meter was used instead of a more accurate NIST tracable spectrometer.

http://i.imgur.com/XqsXP.jpg

http://i.imgur.com/J2pxu.jpg

>Glass absorbs light? Interesting theory or use of the word "absorb"

Ok......

Of course glass absorbs some light. For example, one can easily construct an "infinity mirror" and easily visualize the absorption of glass.




This is optics 101 here and why camera lenses will have optical coatings to help with the internal reflections of light that causes greater absorption. For example, a camera zoom lens with 20 optical glass elements (up to three glass elements may be used to create a single lens to ensure that the light is all focused to the same point) without coatings and much of this light would be lost due to internal reflections. The glass elements will have slightly different refractive indexes to accomplish this focusing of different wavelengths of light and help eliminate chromatic aberrations.

These internal reflections are absorbed by the glass.

Prime lenses don't have this problem as much but will still have optical coatings so that not as much light is absorbed by the glass.

In typical imaging systems, this improves the efficiency since less light is lost (wiki quote). They are referring to the absorption of light with glass. The transmittance of a single element (two surfaces) may be as low as 90% depending on the type of glass with no optical coatings. (edit - here's a sample transmittance chart).

Due to being reflected by a back coating the light of a "normal" mirror has to go through four uncoated surfaces which is why second surface mirrors should not be used as previously mentioned.

There will also be some scattering inside glass that also gets absorbed since glass is a non-crystaling material which is more prone to irregularities called grain bounderies.

An good example of glass absorbing a lot of light is the presidential limo with four inch thick glass (and polycarbonates). This is really more due to the Beer-Lambert Law because of the thickness of the material:

https://s-media-cache-ak0.pinimg.com/736x/8e/24/86/8e2486078d55ced2743d7d6ba5e2be1b.jpg

You wanted interesting theory on glass absorption and I just kindly gave it to you. Lighting and lighting theory are my specialties and honestly you are going to get way above your head here if you do not even understand the basics of how glass behaves.

edit- if you want to learn more buy this book (I have the 1st edition):

https://www.amazon.com/Introduction-Radiometry-Photometry-Ross-McCluney/dp/1608078337

> I haven't stayed up on the literature focusing more on lighting.

Hey Eris, someone at /r/spacebuckets once recommended William R. McCluney: Introduction to Radiometry and Photometry to me and the info is denser than some dank nuggets.