How do anti-reflective coatings let MORE light in through the lens?

[Gauss44]

---

Members do not see this ad.

Or can you explain what this statement from TBR means, "No light reflecting means more light in through the lense - energy must be conserved after all."? How does MORE light get in?

The whole paragraph goes like this (for context): "Thin-film interference has industrial applications as well. Thin coatings of plastic are often sprayed onto camera lenses when photographers need anti-reflective lens. No light reflecting means more light in through the lense - energy must be conserved after all. The wavelength selected to have the least reflection (e.g. yellow-green, as it is in the middle of the visible spectrum), determines the optimal thickness of the anti-reflective coating of the lens. This coating serves as the thin film, which creates destructive interference of that specified wavelength."

 

[POA AFLAT POG]

Apologies if I can't explain this well but here it goes.

What anti reflective coatings do is that they allow more light in through the lense compared to a regular lense. If you shine a flashlight at the regular lense some of that light would be reflected back, away from the lense. If you were to shine that same flashlight at the anti-reflective lense all that light will pass through the lense. I think this is what the book is trying to say. If there is no light reflecting where did that "reflected" light go? Probably through the lense (since light is a form energy and the law of conversation of energy states that energy cannot just disappear)

So how does more light get in? The spraying of the anti-reflective coating creates a thin film where you get three indexes of refraction: air, film, and glass. The different indexes cause the light that would normally become reflected to destructively interfere with each other and therefore have no reflection. Since there is no reflection, all of the energy from the light is considered to have passed through the lens.

The last part seems a bit confusing so maybe someone with a better understanding can explain it better.

Wiki

 

[Gauss44]

I'm still not sure I'm getting this.

1. Is the anti-reflective coating of, say glasses, on the side of the lens where your eye is? Because if that's the case, then I can understand how using coatings with indices of refraction between 1.5 (glass) and 1 (air) could keep the critical angle wide and therefore LET MORE light in.

2. Another guess about how this works would be that when reflected waves cancel each other out with destructive interference, they are no longer colliding with incoming rays as much. So, as a result, the incoming rays can arrived without colliding with those rays that have cancelled out.

3. I don't know how the cancelling out of waves by destructive interference would square with the conservation of energy.

Please explain if you can.