Wow, someone actually made a cheap 1D flashlight! It's quite common to end up with an oddball single D cell since many gadgets take 3D cells, so I have long wished I could get a cheap 1D flashlight.

I have no illusions about a 1D light being a barn burner. In fact, due to the higher internal resistance, a 1D light probably doesn't give you as much runtime as you'd expect compared to a similarly bright 1AA light unless the amperage draw is very low. I suspect that this light doesn't draw much power, so it should last a good long time and really take advantage of the higher capacity of that big D cell.

I imagine that this might be a good replacement for a candle in a power outage, to provide a low level of ambient light to a room or hallway, without the risks of having an open flame around.