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    Led lights
    From: Ken James
    Date: 2003 Nov 26, 01:19 -0600

    Just browsing the list,  noticed the thread about led nav lights. Since I am
    the guy most likely referred to in part, I thought I might try to clarify
    things a bit.
    
    I am the designer and manufacturer of LED navigation and cabin lights for
    Deep Creek Design Inc.
    
    There has been some question about intensity/brightness of pulsed LEDs. In
    that regard, it is a well established fact that the phenomena known as
    "flicker brightness enhancement" is real.
    What it boils down to is that for the human eye, a periodic train of light
    pulses of correct pulse duration and duty cycle (on-off %) can look
    'brighter' than the same amount of light spread out uniformly over the same
    time frame. The explanation seems to be that the eye does not have enough
    time to tell the brain the light is off before it comes back on, and the
    peak value gets taken for the average value, more or less.
    
    Now, does this mean that a LED can be made more 'intense' this way? NO!, in
    most cases, the average "intensity" will be less than a continuously
    operating led, so this may be where those folks who dis-regard the effect
    may be coming from.
    The advantage is that the pulsed LED will *LOOK* brighter "for the same
    average power" as a continuously operating one, in other words, by pulsing
    you can get a light that looks just as bright, or almost as bright, as a
    continuously operating one that uses a lot more power (up to 80%
    more...that's almost two months run time on one group 27 battery for an
    anchor light that can be seen from at least two NM, instead of only one
    month).
    The catch is that it costs more money for this type of LED array 'driver',
    and it may need to use more leds, due to needing to spread the thermal load
    (at higher peak values) out over more leds, so it is a somewhat more
    expensive design.
    
    As far as can the LED turn on fast enough, yes, they have very rapid rise
    times and there is VERY little time lag...it is one of the few light sources
    that can be pulsed to good effect this way because of this fast rise time.
    There are other things that can be done with pulsing also such as trading
    off  the duty cycle on-off and intensity  within the correct parameters will
    result in constant brightness, changing the duty cycle by itself can result
    in loss-less dimming, ect.
    
    Transients and overvoltage can indeed be a severe problem for electronics of
    all kinds in the marine environment.  LEDs are VERY sensitive to voltage
    changes, a change in voltage of only 10% can result in a current change of
    100 times. So, for these reasons and in order to maintain uniform
    luminosity, it is a very good idea to use an electronic LED driver that can
    protect the LEDs and regulate the the power to them.
    There are many ways of doing this, but few take the time or spend the $ to
    do  it well, with the result that the LED array or driver may fail
    prematurely. Not only that but many driver designs can waste almost as much
    power as they supply to the leds.
    
    As far as adequate intensity of LEDS for the application of boat navigation
    lights, LED intensity has improved a lot recently. There are now five watt
    LEDs (five watts for ONE LED...) that each one are as bright as a 60-80 watt
    incandescent bulb...no joke! So, it is just a question of matching the LEDs
    to the specific application.
    
    One thing in this regard NOT mentioned is color sector coverage and
    cut-off...some LED lights are designed only for power boats, they do not
    have enough vertical coverage, and there are some out there of questionable
    color sector separation...it is not enough to use bare 'lamp' LEDs in a
    fixture with a screen or filter, or even a vertical filter on the
    array...neither scheme will  provide the required sector separation. You
    must use some type of optics installed on the array itself (or a custom
    designed LED, an animal which does not exist!).
    For example, without proper separation, there will be a 'zone of confusion'
    where you will look like a somewhat orangeish-white light for as much as
    thirty degrees from dead ahead with leds in a bow combo light, way more than
    the regulations permit.
    
    This is an area of technology that is changing rapidly and becoming ever
    more useful for us sailors (of all types).
    If any one would like more info, I would be happy to mail them a CD with all
    sorts of LED stuff, (prob. more than you would ever want to know! ;-) )even
    how to design your own simple led lights, and the CD has a scads of other
    very useful info...I will mail them as long as I have CDs, can't cover
    dozens, but...give me a holler off list if you want the info at
    nautikat@gulftel.com
    Ths is NOT a 'commercial' CD, just something I put together to send to some
    of my cruising buddies...but I include a bunch of stuff about LED lights on
    it as well, so it could be good here.
    -Ken
    
    
    

       
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