That's interesting. Mine don't darken at all, if very little. Instead they appear to shift the light, making a white-blue turn green, and turning yellow into orange - almost red. Doesn't help much with glare or light intensity, but the colour change means that those LEDs don't burn into my eyes causing me to see a black spot for a few minutes.

I've heard to keep away from normal " yellow tinted night driving sunglasses" or fishing/daytime polarized glasses, but I don't know the exact science.