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    Re: led lights>
    From: Ken James
    Date: 2003 Nov 26, 14:53 -0600

    >
    > I hope he won't mind if I cast a somewhat leary eye over his following
    > assertion.. Have these observations been confirmed
    > independently, and can Ken provide a reference?
    
    Yes, of course. Some of the info is on the web, which makes it easy...here
    is one site, a good one...they cover both Bloch's law and the Broca-Sulzer
    effect;
    
    http://webvision.med.utah.edu/temporal.html
    
    more
    
    http://color.eri.harvard.edu/stevhom2.htm
    
    http://www.uctc.net/papers/207.pdf
    
    
    http://216.239.37.104/custom?q=cache:_3YjBBZi2uMJ:arapaho.nsuok.edu/~salmonto/VSII_2003/Lecture13.pdf+%22temporal+summation%22&hl=en&ie=UTF-8
    
    Also, ON has a PDF document that metions pulsng leds to ...and there are
    many many more refs if you google the keywords in these documents.
    
    Were they made using the
    > same type of LED emitter?
    
    A LED wasn't used as the light source as far as I know...but the important
    thing here is the freq., chromoticity, intensity and duration...all of which
    can be replicated quite easily by LEDs.
    
    Was the apparent brightness determined by
    > human-eye assessment or by some instrument?
    
    The intensity was measured, the apparent brightness was subjectivly
    obsereved and also measured as nerve action potentials in some experiments
    and then correlated.
    
    Does the observation apply in
    > circumstances (duty-cycle and period) in which the light APPEARS to the
    > human eye to be steady and not pulsed (even though it IS pulsed) because
    > otherwise the colreg requirements would not be met?
    
    Yes...however, the COLREGS do NOT say that a light can not have an
    observable 'buzz' only that it must be steady...if they DID, some lights
    might fail (IE Euro 50 HZ AC, I have seen some of them 'buzz' myself) but in
    any case, I comprimise with our lights to achieve percieved flicker fusion.
    
     > If indeed the above assertion of 80% longer battery life is confirmed,
     than such a pulsed design would be well worthwhile.
    
    I have a MKIII design of such an anchor light on my boat...it stays on all
    the time as a long-term test. It uses one amp hour per 12 hours run time out
    of 24 (the light has a built in day sensor) It was recently seen by several
    people on a small boat over the water against the background lights of the
    marina at 2.7 NM.
    I say as much as 80%...it might be less, but the least amount I  have seen
    is that we get almost a 50% gain in run time for the same visibility above
    those using a typical DC-DC converter type driver.
    
    I have now sold upwards of one thousand FirstStars...no one has ever
    complained that it was not bright enough. In fact, with the new MKIII model,
    it is often the brightest light in the anchorage, as well as the lowest
    power.
    >
    that each one are as bright as a 60-80 watt
    > >incandescent bulb...no joke!
    >
    > That's new, and interesting, information. Does it refer to mean power,
    > rather than the peak power level achievable in a short pulse?
    
    No, continious power is what is spec'ed, these are LumiLed leds, the
    measurment refers to illumination. It puts out up to 80 lumens in a very
    wide beam of about 140 degrees. This is as much as a typical 50 to 60 watt
    incandesecent light bulb used on a boat.  Right now, the 5 watt is only
    available as samples (if there are any left), but they have other lower
    power one and three watt models. I am awaiting the 'warm white' models for
    my newest designs.
    >
    
    > Ken claiming that those problems, of sufficient light output at every
    > azimuth and elevation within the defined sector (especially for sailing
    > craft) and sufficiently sharp cutoff outside it, have now been resolved?
    
    NO, I am saying that if you use leds that provide sufficient vertical
    coverage, you WILL NOT have CORRECT horizontal coverage without excess spill
    over unless you apply an additional optical elemnt(s) as part of the
    solution. You must use an optical element of some type...which I do on our
    lights...Perko acknowledges this problem by requireing their sidelights be
    mounted a min. distance back on the coach roof (BTW, their led side lights
    are rated for power only, not enough vert. coverage for sail)
    
    > Can he supply polar-diagram figures to convince us?
    
    No, not for our light, unfortuantly, at least not yet...our light has been
    measured by a testing lab...but I do not have that info as yet...it was done
    by a UL lab and they are being very slow. I do test them myself, but I do
    not have a lab apperataus. My own tests do show a sharper cut off between
    sectors than a normal fixture with an incandesecent bulb, and this is also
    observable by comparing our light to a normal set up as a smaller 'zone of
    confuson' from dead ahead.
     HOWEVER...a look at the manufactures polars for the leds will show what the
    problem is. If you examine the polars for a 60 deg led, (60 deg provides the
    correct vertical coverage) you will see that it has a broad 'fuzzy' boarder.
    If you bring these boarders close together you get too much spill over. So,
    if you use a led that has a sharper boarder, it is too narrow a beam to
    provide correct vert. coverage. If you merley use a simple vertical divider
    between the sectors it will not be sufficient, given that you are tryng to
    intercept a 3D conical volume with a 2D device, in effect. You must have
    proper design to acheive good sector division. I do it with optical elements
    on each and every led as needed.
    
    design for the  with a    Has any LED nav-light
    > (bow or masthead) been given any sort of type-approval by any regulating
    > authority?
    
    Not sure...it will happen soon, though. A number of them are working on the
    problem...
    
    We small-boat sailors are living in hope, and as soon as the
    > answer is "yes", we will be beating a path to the door of the supplier.
    
    Well, I have sold many of my lights to sailors all over the world, including
    the likes of Steve Fosset, Nigel Calder, Webb Chiles, the Sleavins, Bruce
    Schwab, several Ocean 60's ect., ect. and they all like them. No, they are
    not certified...but they are brighter than the bulb they replace, most of
    the time. I can make them as bright as needed...but our stock models are
    made to appear as bright, or nearly as bright (not all bulbs/fixtures are
    the same) as the 'normal' 25 watt bulb.
    >
    > Ken's mention of "a custom designed LED, an animal which does not exist"
    is
    > intriguing. If a single LED is now capable of supplying enough light,
    there
    > may be a big enough market to encapsulate it in an a special lens-moulding
    > designed to meet the colregs requirement.
    
    The market would have to absorb tens of millions of leds before a design
    would be specialy made for it.
    
    And then that single light would
    > be nearly a point-source, in which case only a small screen, in a
    > reasonably-sized housing, would be sufficient to obstruct aany last
    vestige
    > of crossover light across the bow.
    
    No, I know that seems reasonable, but it is not correct...leds are not light
    bulbs and often require their own design optics to meet the specs of any
    given application...in addtion, the new leds have many other design
    considerations, such as they must be driven with a tightly regulated voltage
    and current supply, active and passive thermal mangement becomes a
    prioriity, and protection from both electrical and enviromental damage is
    paramount for reliable operation. -Ken
    
    
    

       
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