I like the A design.
Totally agree a side physical switch and one mode would be the easiest to remember and use for many. Large diameter, has lots of grips and durability.
I ended up giving a tactical Klarus to an aunt for Christmas because it had one switch at the back, and then the paddle right next to it to adjust modes. It was what I thought would be the easiest for her to remember.
It seems we all have different views on what a gramma light should be like.
I’d say a 1 mode 100 to 150 lumen light with lithium primaries that will last for years, with a normal 1208 Omten reverse clicky as a side switch is quite ideal.
And preferably warm white, because not a lot of blue passes through the lens of an old person’s eyes anymore.
But then i’m thinking of people older than my mother of 75 years old, and she only uses her flashlight a few times a year.
Maybe the target audience is around 60 years old and using a flashlight regularly rather than having a flashlight within reach but only for emergencies and other exceptions.
For that younger (less old) group of more active flashlight users, indicators, charging ports and several modes would be a plus.
For the older group who want to have a light for emergencies or exceptional situations, those extra features are a fuss rather than a plus.
They don’t want a rotating ring interface, they want an ON / OFF light switch on that thing.
I think we should keep in mind that not all grandma’s are elderly people. I once worked with a woman who was a grandmother at 29. Yes you read that right. She had her first daughter at 14, who then proceeded to have a kid also at 14.
I didn’t get married until I was 34 so I had a lot of catching up to do with having grandkids 
The way i see it there could be an entire line of Grandma lights, each with different features (rotary, side switch or tail switch, lithium/usb rechargeable or AA, etc).
But if we want to make one light it should be either AA or lithium/USB chargeable (4.0V termination), have a side switch or proud tail switch, be 250 lumens at most, 1 mode, simple click to on, click to off, no parasitic drain (or last years on a charge), and not have any surprises.
As i mentioned the Shiningbeam Romisen RC-G2 has been the best grandma light i have come across. I put a fully charged Eneloop in it and it worked great.
Or the FC11 with UI changes and no tail magnet.
I’m for a ring on the head of a flashlight or a magnetic slider with 3 positions - off, 15-30, 100
+ charging, preferably not usb, but usb + from the network - it is easier for old people to plug the flashlight into the socket and wait
And an important point about charging, since old people like to discharge batteries as primary batteries (to death). The flashlight should start signaling the need for charging much earlier than for flashaholics, for example at 3.8 volts and turn off at 3.6 volts, and also finish charging at 4.1V to prolong battery life. At the same time, signal with the help of flashing, built-in speaker and vibration “Charge me! Charge me! Charge me!”
Well, and built-in 21700 battery for long life
If we are designing a light from the ground up i would go with 21700 and 4V cutoff and your early recharge indicator is an nice idea.
USB recharge is much cheaper than mains charging, though i do like the idea of mains charging.
Frankly I would go with USB becasue may seniors now have phones and can handle a USB C but also another family member can charge it as they would change the batteries if the senior could not do that themselves.
Large rotary or sliding switch at the front.
No secondary switch.
The switch should be mechanical, or if it is not fully mechanical it should have a mechanical off position. Parisitic drain is bad design.
No blinky modes. If it isn’t stepless something like Off > Moonlight > Low > Mid > High.
Must accept AA, C, or D, NiHM and Primaries.
No Li-Ion or LiPo for obvious safety reasons and poor availability in shops.
No low voltage cutoff or flashy lights that granny doesn’t understand, it gets dimmer and dimmer until there’s no more juice.
No onboard charging, needless complication.
Flats or flattish profile so it doesn’t roll is nice.
Decently wide head and tail for standing up.
I would suggest that 1AA is normally too small so if going 1AA make the body pretty big and longer than it needs to be.
Agree with other comments that Romisen RC-G2 was a good grandma light, gave Nan one of those and she liked it but commented it was too bright for close up stuff. Was surprisingly tolerant of the leaky old Zinc Carbon batteries she used (I gave her Eneloops but even the basic charger was too complicated).
Side by side 2AA would be nice for a flattish profile, doesn’t roll, comfy in the hand, longer runtime, pocketable and very unusual and old school. Perhaps a little short.
Side by side 4AA also excellent. Fenix LD42 is near perfect.
2C is also a nice size in the hand, awkward battery requirement but can adapt down to AA.
D’s are IMO too chunky, excellent runtime though.
High CRI 2700k, Nichia 519a probably.
Body colour options, Nan didn’t like matte black.
Purple and silver were favourites.
I propose silver, use type 2 anodising, shiny silver looks nicer than dull grey type 3. Type 2 is durable enough.
Silver is old school, timeless and not as divisive as colours can be so should have wider market appeal.
our family has gone down this route before.
here is what we learned:
1. two modes: OFF and ON. Strobe is the Devil and Ramping is a Demon.
2. use common batteries found in every store in town. zero/none rechargeable.
3. bigger is better than smaller. soda can would be the upper limit.
4. one mechanical control which makes an audible “click”.
5. finally, cheap. that way, it is easier to have extras.
our secret: we “hid” an extra one on top of the refrigerator.
when the envitable call came: “where is my flashlight?”
we told them where. it was like managing two
4-year-olds with their toys.
All of the fancy stuff that we love here on BLF, is counterproductive when dealing with older folks in an some kind of “emergency” situation.
Can I say it again? KISS.
And, yes, more is better, so affordable is the way to go.
Nobody know more about ‘grandma light’ than one true grandma. That is definitely a key message!
Haha, please no mind my man. It is just one small idea I suddenly think up 
Hello Terry,
Happy New Year!
Having followed this thread and D'Jozz's before it, I must ask for clarification if this project is truly about age, or is it supposed to be about physical ability and temperament? Because as a senior citizen, I can tell you that they are not mutually inclusive in terms of criteria.
Got it. That is exactly my purpose. I want to know what the older people truly need, not to make a decision based on my personal subjective speculation.
Happy New Year Knot!
It is supposed to be about physical ability and temperament my man.
I hope this project can make people who really need it with more convenient for use light.
That would be two options. My idea is that the Tactical switch will only be control the ON/OFF. Then the rotate ring add one moon mode. In this way, we can set the friction of the ring into a very low value.
Thanks for your reply my man. How about that, use moon mode replace to the
switch-off?
Haha, thanks for your great vote my man. I just think that life should have one more options, and different people may have different needs.
Got it! I need to consider where to place the battery indicator now.
Thank you my man. And thanks for Mr. djozz’s amazing idea again. One great flashlight enthusiast!