Monday, April 18, 2011

Buying goggles for summer ?

     I just bought new sunglasses for summer B-) It makes a lot of difference if you are driving/travelling for even an hour in bright sunlight. I brought a pair of nice polarised goggles. Thought, would share some details about it here in case somebody finds it useful.

      First- why 'polarised' goggles(hereafter PGs) ? Do they make any difference ?
      Polarised googles are aimed at reducing 'flare' (bright, undesirable reflection in simple words). Flare quickly causes eye fatigue and I can say this is true with experience. By reducing flare, PGs essentially make your driving comfortable by keeping your eyes relaxed instead of strained (often unconsciously) to compensate against the flare. But, as might be portrayed by some shop owners, PGs by no means are a cure-all against bright sunlight. I guess, in general they would make 10-15% difference in the long run at max, over normal non-polarised goggles.

      In a shop, how to make sure that the pair you are planning to buy is really a pair of PGs ?
      The test is really simple - put on the shades and look at anything that uses LCD technology for display. That would be - mobiles, digital display watches, LCD monitors, LCD TVs, laptops and what not. Now tilt your head sideways while looking at the LCD display. Try both, left and right sides. With any of the tilts, if the brightness of the display changes appreciably or you see wierd colours on the display, then you can be sure that the goggles are indeed a polarised pair. If not then not! With a mobile, the test is even simpler, just hold the mobile in front of your eyes and rotate it in the same vertical plane. The reason this test works is because LCDs themselves work on the principle of selectively blocking light on the basis of its angle of polarisation.

      On road, in which cases would a PG help and in which would it won't ?
     Almost all PGs are constructed such that their axis of polarisation is perpendicular to the plane of ground (road). Thus, any light being reflected off the road will be effectively(but not perfectly) attenuated. At the same time, any light reflected off non-horizontals surfaces like vehicle bodies, windscreens, advertisement hoardings etc will not be affected by PGs. Hence, PGs are best suitable and effective for highway driving esp. if it is a 'cement road'. In city traffic, we hardly get to see the road surface, leave alone flares from it :) However, it is good to get PGs just in case you decide to travel far. Also, non-glass PGs (thanks to polymers!) are not very expensive. One can get them starting 350-400 INR.

Happy Polarising ;)

PS: For photographers - buying PGs instead of a proper polarising filter can be a makeshift way to saving a few bucks. However, don't expect the same fidelity. Also, since PGs are only linear polarisers, your AF sensors might be misled :)

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Cartographer said...

I am getting PG's this time around. Thought provoking and polarised article ;)

Pranav said...

He he, thanks :)