Standard photochromic visors for your motorcycle helmets are becoming the next "in" thing. The electronic ones are still a tad too expensive and difficult to get, but standard photochromic visors are now available at reasonable prices. But some companies offer both, like the one below.
If you tend to ride long distances, often you have the problem of changing light conditions, dark to sunny, to cloudy, to long tunnels. You can't stop every time and take off your sunglasses, or worse, change visors.
Italian Raleri have a universal visor for most motorcycle helmets that changes color reasonably quickly, and can be fitted rapidly onto any visor. It doesn't replace your visor, it sits on it.
Watch the installation video, you'll see it's done quickly and easily. In fact, knowing my two left hands and inability to even change a light-bulb in the house, I think even I could do it.
The photocromic visors are not expensive. Count on €36.90, but if you've got an Arai helmet, you'll need to order a special model (for the same price).