Let's be honest; Trying to turn on / off almost any light or torch while wearing heavy mittens or gloves is not going to be easy. Personally I can't fathom wearing mittens while riding a multi-geared bike. Without articulated fingers available it's going to be real hard ( if not impossible ) to change gears. Working a light would be the least of my worries as ( what was said by others ) I could always remove a glove to turn the lamp on or off. Changing modes not going to be easy but since I have a lamp that has a single button remote switch I can make due.

For me the hardest part of riding in cold weather has to do with not being able to easily access my phone's touch screen if I'm wearing double gloves. If it's not too cold I wear a single pair of full finger gloves with a small section cut out on one finger so I can still operate my phone's touch screen.....Getting back to the original argument, I really don't see the point in having the ability to operate a bike light vs. a torch ( wearing heavy mittens ) as in my opinion a bike light would be easier to operate as long as you chose the right light. Then again I own a Wiz-1 which while sold as a bike light happens to be very torch-like. The mode button on the Wiz-1 is pronounced enough that wearing heavy gloves should not be a problem.