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#280854 - 05/29/16 09:52 PM Signal mirror 2x3 v 3x5
WesleyH Offline
Journeyman

Registered: 05/26/16
Posts: 98
Loc: OKLAHOMA
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?

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#280856 - 05/29/16 09:58 PM Re: Signal mirror 2x3 v 3x5 [Re: WesleyH]
hikermor Online   content
Geezer in Chief
Geezer

Registered: 08/26/06
Posts: 7371
Loc: southern Cal
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.
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#280877 - 05/30/16 08:33 PM Re: Signal mirror 2x3 v 3x5 [Re: WesleyH]
Mark_R Offline
Old Hand

Registered: 05/29/10
Posts: 856
Loc: Southern California
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.
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Hope for the best and prepare for the worst.

The object in life is not to be on the side of the majority, but to escape finding oneself in the ranks of the insane

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#280880 - 05/30/16 11:24 PM Re: Signal mirror 2x3 v 3x5 [Re: Mark_R]
hikermor Online   content
Geezer in Chief
Geezer

Registered: 08/26/06
Posts: 7371
Loc: southern Cal
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.


Edited by hikermor (05/30/16 11:31 PM)
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#280884 - 05/31/16 03:32 AM Re: Signal mirror 2x3 v 3x5 [Re: WesleyH]
rafowell Offline
Enthusiast

Registered: 11/29/09
Posts: 230
Loc: Southern California
Originally Posted By: WesleyH
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?


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".
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A signal mirror should backup a radio distress signal, like a 406 MHz PLB (ACR PLB) (Ocean Signal PLB)

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