I don’t know a single lifeguard who works an outdoor pool without sunnies. We tend to live in them. So much so, that if you forget them you’re shielding your face and squinting with tears running down your cheeks.

But to really see below the surface of the water sunnies need to be polarised. Polarised sunglasses are coated with a filter that allows light travelling vertically to get through, while blocking out light travelling horizontally. So light shining down from the sun gets through while light travelling off water, snow or the windscreen of the car in front is blocked.

If you’re like me and you’re too tight to fork out $300 for a designer label pair, then you head down to the local chemist. There you’ll find a huge range of look-a-likes for around thirty bucks. The problem is, you look at that little sticker on the lens that says ‘Polarised’ and you think really… for thirty bucks?

But, there’s a quick way to tell and it’s because of the way the polarising filter works.

As we’ve discussed, if you take a pair of polarised sunglasses and hold them up to the window, all the light travelling horizontally is knocked out. If you take a second pair and hold them at ninety degrees they will now block out all the vertical light. Two polarised lenses held together, with one at ninety degrees will block out all light and go black. The image at the top is an example of this.

Many of our phone and camera screens are polarised too. That’s why if you’re wearing polarised sunglasses and your turn your phone or camera on it’s side, the screen looks like it goes blank. Take your polarised sunnies off and the screen comes back on.

The whole point to this is that if you want to have a better chance of seeing a person below the surface of the water in a pool, you need polarised sunglasses. If fishermen won’t go fishing without their polarised sunglasses we’d be crazy to turning up in a Coroner’s Court saying ‘Oh, I don’t really use them, your Honour’.

Making polarised sunglasses staff policy is a good idea. Get a box of el-cheapos to keep at the pool so that if someone forgets theirs, they can borrow a pair. And, then occasionally walk around with your polarised sunglasses and check that theirs are polarised too.

P.S. It might also be worthwhile checking how helpful they are in a bright pool hall. Don’t just assume that because it’s an indoor pool that they won’t help. Do the test, and do it under a variety of lighting conditions.