In the horticultural world, there have been different statements and comparison in terms of these two AR coating method, but never stop till now and may not in the future.
Here are some theories regarding this difference between the two methods. It is not just empty talking on paper, but can trigger some basic thinking in addition to untraceable testing data.
The refractive index of AR Layer
The index of refraction should be a fixed number according to Fresnel Formula: n(AR Layer)² = n(Air) x n(Glass), for this reason so the evenness of Nano-Micro structure is critical to keep the refractive index fixed.
The micro structure of AR layer under Etching method is more uniform than Sol-Gel due to its chemical etching in certain time with reagent, instead of a extra layer of coating covering the glass surface.
2.The AR Layer thickness
Considering the half-wave loss, the AR Layer thickness should be stable to be exactly 1/4 of the wavelength. So similar theory here: the Acid etching guarantee a AR layer with stable thickness, especially compared to the sol-gel dipping coating.
3.The production process(last but most important)
For the Etching method, the AR process is the last step to finish the final production after tempering process, but for Sol-Gel it needs to do AR coating firstly then head to tempering, so the AR coating structure is easily affected during tempering process with 700℃ high temperature.
There will be always better technology for the horticultural glass, but we are confident Etching AR is a better choice to get a long life guarantee with above advantages, after all the greenhouse glass is used for many years and longer shelf life could create consistent profit for growers.
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