I realise this topic has been done to death and there is a wealth of threads with peoples opinion on what the best sunglasses are, however I'm struggling to understand the restrictions specifically relating to photochromic lenses and subsequently which sunglasses I should go for.
Under HP&L the JAA say that photochromic lenses are generally forbidden due to the time taken for them to adjust to changes in light. Indeed, a number of threads on here quote Bad Medicine on the matter of sunglasses, specifically the bit that says:
Back to the original issue of photochromatic lenses. Photochromatic lenses have several disadvantages that render them unsuitable for use by pilots.
Firstly, their transition times are relatively slow. Photochromatic lenses take about five minutes to increase their density to the level of sunglasses, but more importantly, the bleaching time from maximum to minimum density can be as long as 30 minutes. Although there is a rapid lightening of the lens in the first five minutes, this may be too long when there is a sudden variation in light during a descent into or under cloud, or because of a rapid change in cloud cover.
Their second disadvantage is that, even when fully bleached, photochromic lenses still absorb slightly more light than untinted lenses. Since vision is critically dependent on ambient light levels, even this small decrease of light reaching the eye through photochromatic lenses is undesirable, especially at night or in low light levels. The inherent degradation of these lenses with time causes them to progressively become darker, as they become unable to reach the fully bleached state. This effectively prohibits their use in flying or controlling air traffic.
So theres me thinking it was a pretty much done and dusted matter that photochromic lenses were a no go for pilots. However in trying to work out what sunglasses to get, the ones from Serengeti have caught my eye. In fact, they've caught a lot of people's eyes from these forums and I reckon a good half of the posts on the matter swear by them. Add to that, most pilot supplies shops sell them and even found one web page saying they were part of the standard uniform for Delta pilots! (not sure if that last one is true or not).
But my dillemma comes from the fact that according to their website, all the Serengeti lenses are photochromic!
So..my question.. Has photochromic technology come far enough these days for it not to be a problem? Or is it that the Serengeti's only adjust from ~10%->25% in terms of light transmittance thus taking a relatively short time, and the issues surrounding photochromic lenses only really apply to lenses that go from completely clear to darkened? Alternatively, when the JAA says 'generally forbidden' it means its not a hard and fast rule and its up to you to make your mind up on what you feel comfortable with?
Any thoughts? Am I good to splash out on these, are am I going to end up with an expensive set of sunglasses I shouldn't be using half the time!
