Does this meet the angular spread requirements for the FAA? I forget the particulars, but the white light pattern has to be seen across a broad swath to the rear and sides of the aircraft, as I recall.
Douglas W. Johnson MD, FACR
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Douglas,
My calculations indicate that the system meets the minimum intensity
requirements but I have not measured this to confirm the calculations.
Here is the calculation....
The FAA requires at least 20 candela for the azimuth range 110 degrees to 250 degrees.
(FAR 23.1391)
The LED I used, LZ4-40CW00 ($15.20 at Mouser),
uses 14 V, drawing 700 mA and puts out 680 lumens.
1 Candela = 1 Lumen/Steradian
The aft-facing hemisphere has 2 pi steradians, so assuming the lightpipe transmits about 75%
of the light the average brightness is 0.75 x 680 / (2 pi) = 81 candela
I sanded the output end of the lightpipe flat, which should make the source approximately "lambertian", which means the amount of light you see at each angle is given just by the projected
area of the sanded end that you see. This means the intensity pattern is an approximate cosine function of the azimuth, peaking in the aft direction.
At 180 degrees azimuth the flux is higher than the 81 candela average, by a factor close to pi/2 so the peak intensity is around 127 candela. At 110 degrees (and 250) measured from the nose, the intensity is reduced to 127 x cosine (70 degrees) = 43 candela.
This is more than twice the 20 candela requirement so yes, the LED/light pipe is bright enough.
If I recall the old Whelen aft-facing white light uses 2 amps, so it is impressive that a little LED drawing 700ma can match it.
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