After the recent discussion about my issue with "Bogus sightable, not really specified who makes it, you guess what it is from the picture" issue. . .

Does anyone have any information or research on the effectiveness of the 3x5 mirror compared with the 2x3 mirror?

It would certainly seem that the larger mirror, the more light you can send downrange . .does it translate into a better chance of being sighted?

The larger mirror is indeed brighter - 15 in sq vs 6 in sq. If made of equivalent materials, is is also 2 and one half times as heavy, which can be a consideration in some contexts. My PFD or float coat always packed a 3x5, while my hiking gear favored a 2x3, while sometimes I just relied on the mirror in my compass.

It would seam reasonable that 2-3 times the area would equal 2-3 times the light, or an increase in effective range of 40%-70%. My limited experience with large reflectors involes patio doors coating with a reflective film. Even at a distance of over a mile, they were uncomfortable to look at.

When at sea off the southern California coast, I have often seen flashes from the windshields of vessels hull down on the horizon, otherwise not noticeable....

The largest "signal mirror" I have ever seen in use was a mirror from a standard bathroom cabinet, employed by gentlemen from Arizona Mine Safety to light up vertical shafts so that we could see clearly what was below, in many cases saving a tricky and somewhat dangerous vertical operation. I have used smaller mirrors as impromptu lights to illuminate dark corners in rock shelters and the mouths of caves- bigger is definitely better.

It's certainly brighter, and can be seen farther[1]. While I'd expect that to make it more noticable, I don't recall any straightup studies on comparative human perception at 5 miles or less (e.g., comparative apparent brightness, perceptibility to peripheral vision, etc.)

In 1905, the US Signal Corps was of the opinion that the difference was perceptible to human vision at 5 mile range. I infer this from the advice in the 1905 US Signal Corps manual to mask down the (4.5"x4.5") heliograph mirror to 2"x2" at ranges of 5 miles or less to make it "less tiresome on the eyes of the reader".

[1]I've seen (naked-eye) the signal from a 3"x5" glass MIL-M-18371E at 44 miles, and a 2"x3" glass Coghlan's at 22 miles. Colonel Everest (who led the survey of India in the 1830s) figured on 10 miles of naked-eye range for each inch of side, which would be a bit less than 24 miles for the 2"x3" and 39 miles for the 3"x5".