Diver0001:
I am *so* happy I blundered across this thread. I believed the CD myth. Got a link?
R..
Short extract from:
http://www.equipped.com/signal.htm
The signal mirror is the most basic and best all-around signaling device. Compact and simple to operate, it has been successfully used for many rescues. While any shiny object can and has been used for signaling (see illustration for how to do so and click for larger image), a purpose made signal mirror is generally brighter and the best are much easier to aim.
In normal sunlight, the flash from a good signal mirror can easily be seen for 10 miles and generally the flash will be visible up to 50 miles, depending upon atmospheric conditions. The record rescue from one is 105 miles, at sea. A mirror will even work on bright overcast days and with moonlight, though with much reduced range. Many experts recommend carrying two as you can then more easily signal in a 360 degree sweep with a little practice. An experienced user can signal up to 270 degrees, sometimes even a full 360 degrees if the sun is high, with a single mirror, but that is pushing it for most users. One mirror per person isn't such a bad idea.
A mirror 4 inches by 5 inches (standard United States Coast Guard size) or 3 inches by 5 inches (standard large mil-spec size) is ideal. Anything much larger gets to be unwieldy and can be difficult to use for extended periods or to aim accurately. Even the USCG size can be awkward for those with smaller hands, especially if it is made of heavy material. The smaller 2 inch by 3 inch size (standard small mil-spec size) work adequately and the convenient size is an asset. There are also a few manufacturers that make mirrors even smaller than this. Generally, the bigger the better, since brightness is partly a function of the reflective area. The other determinations of brightness is just how reflective the mirror actually is and how uniform and consistent the reflected beam is, which is determined by its design, the materials used and its condition.
NOTE: We are often asked about, or see the recommendation online and elsewhere, the use of a CD-ROM as signal mirror. It is shinny, reflects light, has a hole in the center, and thus looks somewhat like a signal mirror. Moreover, many of us have lots of useless CDs around, AOL continues to send many of more of them, thus its appeal.
In tests a CD proved to be only about 20%-25% as effective (distance and brightness at distance, judged subjectively) as a 3 x 5 mil-spec plastic signal mirror, a bit more effective, but not even 50% compared to a small 2 x 3 mil-spec plastic signal mirror. It would compare worse against higher quality mirrors.
From an operational persepctive, in an After-Action Report of a major SAREX (Search and Rescue Training Exercise) conducted in 2001 by the Colorado Wing of the Civil Air Patrol, the conclusions were, "that "victims" who had never used a signal mirror (with the aiming hole in the middle) were able to use them effectively,
while CD's (AOL etc.) are useless as signal mirrors."
It also has the disadvantage of requiring two hands to aim it as compared to a signal mirror with an integrated aiming device, the hole is not an aiming device. The mil-spec plastic mirrors also float, the CD may or may not, and certainly not as well.
Given that a good signal mirror is not very expensive and is the most effective daytime (sunlight) signaling device, using a CD hardly seems worth the savings.
Not to say you couldn't be rescued using a CD. People have been rescued using the hologram on a credit card to signal with and the CD is far superior to that small reflective surface. A CD makes a decent improvised signal mirror compared to many other options and since they are essentially free, it may be worth carrying some for other members of your crew or party to use, multiplying your signaling capability.
However, we cannot recommend a CD as a primary survival signaling device.
