I am seeing more and more led navigation lights designed with no optics or shielding to prevent the colors mixing between sectors. This is an issue that is often overlooked by hobbyists, DIY'ers, and those who do not fully understand what is required of such a light.
If you think this is an unimportant or trivial problem where such lights are concerned, take a look at a led nav light with and without a method applied to correct this problem here; scroll down on http://www.firststarled.com/products.html A normal nav light that uses an incandescent bulb solves the problem of color sector overlap by using colored filters, and placing the bulbs filament, which is thin long and vertical in such a light, behind the filters in such a manner that if you take a horizontal plane 'slice' through the fixture, all the rays going through the filter between the edges from one color and the next will be coming from what seems to be a single 'point source' at the center of the fixture in such a way that any two rays that are next to each other will diverge at all times and not mix, so if one goes through the red filter and one right next to it goes through the green filter, they cannot mix. In the real world, some mixing does occur but it is relatively slight with a good design. And BTW with a good led nav light design there will be even less overlap than with a 'normal' light! Now if you imagine an led which emits a cone of light, but a cone that does not have a perfectly sharply defined edge or boundary, you can start to see what the problem is regarding color sector overlap with led nav light design. The cone has a 'fuzzy' edge. If you make the cone smaller it will have a more sharply defined edge but then you will soon get to a point where it will not have enough beam spread to be useful as it will need too many leds to make the required horizontal and vertical coverage required with no 'nulls' or dark areas between cones, and that point will come before the beam is sharp enough to prevent color sector overlap between sectors and still maintain sufficient brightness all the way up to the edge. Again, when you put the narrow beam leds conical emission patterns next to each other, to avoid 'nulls' or dark areas you must overlap the beams more as such a beam falls off sharply on the edges and would result in incomplete filling of the sector space, and with a beam that has insufficient vertical spread you will need overlap there also. For a light that uses colored leds and shines through a clear fixture, on the edges where the colors meet you will have a problem, if the colors overlap and mix you will get a dangerous confusing display. You must use some form of shielding or optics to prevent this. Considering a led light that uses either colored light or white light leds and shines through a colored lens fixture, because the multiple leds are emitting a pattern of light that does NOT posses the property of the incandescent bulb filament in the above example, that is the leds make a pattern that is not a 'point source' in a horizontal plane 'slice' originating in the center of the fixture, the result is you can have an led that shines through the edge of a color sector behind the fixtures lens but then the rays will go on to converge with another leds rays further from the light. If you had an led aimed from behind the lens, through a colored filter, but aimed so that the rays it emitted crossed from one side of the color filter to the other after they left the fixture, that would result in color sector overlap. It would make no difference if it was a colored led behind a colored lens or a white led behind a colored lens, you would get overlap, as with the white led it would change color then converge. If you aim the leds that are directly behind the edges of sectors such that the edges of their conical emission pattern is straight toward the sector edges you then must insure the cone is not too 'fuzzy' at least not where the sector edge is supposed to be, otherwise it will not maintain sufficient intensity all the way to the edge, or it will overlap as in the above examples. Colored filters alone will NOT solve the problem of color sector overlap with an led nav light! Once again, the solution is shielding or optics. Companies like Perko and Orca Green (and me) go to a lot of trouble to see that this problem of color sector overlap cannot happen, if you look at their led combination navigation lights such as their tricolor models you will see that they have part of the fixture providing shielding for Perko, Orca Green uses the leds aluminum heat sink as shielding, and I use shielding on the leds and also the leds copper heat sink to prevent internal reflection. But be warned, there are now many manufactures offering led lights that use no optics or shielding to address this potentiality deadly problem! -Ken _______________________________________________ Liveaboard mailing list [email protected] To adjust your membership settings over the web http://www.liveaboardnow.org/mailman/listinfo/liveaboard To subscribe send an email to [EMAIL PROTECTED] To unsubscribe send an email to [EMAIL PROTECTED] The archives are at http://www.liveaboardnow.org/pipermail/liveaboard/ To search the archives http://www.mail-archive.com/[email protected] The Mailman Users Guide can be found here http://www.gnu.org/software/mailman/mailman-member/index.html
