# Anti reflective coatings.... Hype?



## techwg (Jun 10, 2007)

How much difference do these coatings really provide. If you take a light and replace the lense with a piece of glass will it really have the effect of "Wow i guess the coating really works" ? What is this all about... Just the loss of a couple of photons here and there, or actual powerful light lost if you dont use them.


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## funder (Jun 10, 2007)

Without AR coating, the reflection rate of each glass/air surface will be around 4%. Thus for a single lens, the lightloss caused by reflection will be around 8%.

Some AR coating can reduce the reflection rate as low as 0.2%, a good coated lens in flashlight can has a transmission rate of 99%.


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## 2xTrinity (Jun 10, 2007)

The difference between plastic and glass is pretty big -- in part because plastic is inherently not as transparent, and it's more prone to getting scratched and consequently dirty. The difference between AR coated lenses and plain glass is the 8% of the light that would otherwise be reflected back. In practice, some of that light will probably hit the reflector again and in turn re-exit the light as spill, rather than throw. That means AR coating will be most significant for fairly high-output lights designed for throw, improvements of 8-10% in hotspot intensity can be expected.


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## LightForce (Jun 10, 2007)

I have an UCL in Maglite and I hardly can tell any difference between UCL and stock window. It's only 8% more efficient. It gives you marginally stronger hotspot and slightly less spill compared to stock.


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## defloyd77 (Jun 10, 2007)

So basically compared to AR lens, the stock one is kind of like a diffuser?


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## LightForce (Jun 10, 2007)

defloyd77 said:


> So basically compared to AR lens, the stock one is kind of like a diffuser?



Yes, it's something like that, but it's not straight a diffuser.

It reflects part of collimated beam backwards and causes this part to be reflected on a bulb and reflector surface. Then, this portion of light leaves torch and behaves like diffused light.


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## CM (Jun 10, 2007)

techwg said:


> How much difference do these coatings really provide. If you take a light and replace the lense with a piece of glass will it really have the effect of "Wow i guess the coating really works" ? What is this all about... Just the loss of a couple of photons here and there, or actual powerful light lost if you dont use them.



Your unaided eyes won't be able to tell the difference. It's a few percentage points of improvement which is a few tenths of a dB. A light meter or integrating sphere will be able to measure. For those that want to squeeze the most out of efficiency, AR is essential. 

Looking at it from another perspective, AR coatings in rifle scopes will allow you to hunt tens of minutes later into sundown (or earlier sun up). Some feel this is nothing, others feel it's significant (I'm in the latter camp). Same with lights.


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