Re: (ET) Ralph's LEDs

["T Humphrey" <thumphrey mynra com>]

Yeah those LED traffic light are catching on big time in NY too!

Generally I like them, they have lots of advantages over the old 
incandescants. However they also have one MAJOR disadvantage, they 
are cool-running. Recently we had a snowstorm. Being early in the 
season it was a nasty wet snow and the winds were particularly 
brutal during this storm also. Well anyway the storm blew the snow 
straight onto the signal lights were it froze into a solid chunk 
of ice. The old incandescents made quick work of this ice melting 
off with all of there usually waste heat, but the LED's just sat 
there, completely obscured. Too make matters worse, the following 
morning was a cold, cold high pressure system, resulting in 
blinding bright sunshine, making the LED signals even harder too 
see. Not suprisingly, many fender benders occurred. Granted this 
doesn't occur very often, but when it does it's nasty.

Unfortunately?, it wasn't enough snow to use the new thrower I got 
from Jon K.

Thanks, Jon  


Stay Charged!
Hump  

>
>
>-----Original Message-----
>From: RJ Kanary [mailto:rjkanary nauticom net] 
>Sent: Saturday, November 22, 2003 11:39 PM
>To: David Roden (Akron OH USA); elec-trak cosmos phy tufts edu; 
William
>Korthof
>Subject: Re: (ET) Ralph's LEDs
>
>
>    I have no scientific evidence to back up  the idea of whether 
or not LED
>signaling devices use PWM power technology. What I can tell you 
is that here
>in the Commonwealth of Pennsylvania, LED signaling is taking 
root. All new
>installs are of that variety, and most PennDot owned fixtures are 
being
>updated.
>     I have noticed a perceptible flicker, in some units. I am 
blessed with
>what computer geeks call 'Fast Eyes'. I have to have a refresh 
rate of 75Hz.
>or higher on my monitor, or I can't stand to be in front of it . 
So, that
>being the case, if there is a flicker there, indicating PWM 
operation, I'm
>the person that would be likely to see it.
>    The signals I have noticed flicker on also appear to have a 
higher
>number of dead elements in the arrays.  Your thoughts ?
>----- Original Message ----- 
>From: "William Korthof" <wkorthof earthlink net>
>To: "David Roden (Akron OH USA)" <roden ald net>;
><elec-trak cosmos phy tufts edu>
>Sent: Sunday, November 23, 2003 8:20 PM
>Subject: Re: (ET) Ralph's LEDs
>
>
>> David,
>>
>> I'm friends with the owner of one of the most established LED 
traffic 
>> signal retrofit manufacturers, and I've been following progress 
with 
>> them for 10 years. Every production unit I've seen uses some 
form of 
>> current limited power supply designed to approximates a 
constant 
>> current supply (with varying effectiveness). Where did you get 
the 
>> information that a pulsed power supply is common?
>>
>> /wk
>>
>> At 09:53 AM 11/22/2003, David Roden (Akron OH USA) wrote:
>> >I recently read something fascinating about LEDs.  Have you 
noticed 
>> >how intense the new LED traffic signals appear?  (At night 
some are 
>> >so bright that the green ones actually are almost painful to 
view.)
>> >
>> >This is how it's done.  The LEDs are driven by a pulsed 
waveform.  
>> >The on current is TEN TIMES their rating, but the duty cycle 
is only 
>> >10% - that
>is,
>> >on (for example) on 1 picosecond, off 9 picoseconds, repeat.  
Thanks 
>> >to persistence of vision, the human eye sees the peak 
intensity as
>continuous
>> >high intensity; but the LED "feels" the average current, which 
is 
>> >just
>its
>> >normal rated current.
>> >
>> >I'm sure the same thing could be done with automotive signals 
(if it
>isn't
>> >already).
>> >
>> >Clever, no?
>> >
>> >
>> >David Roden - Akron, Ohio, USA
>> >1991 Solectria Force 144vac
>> >1991 Ford Escort Green/EV 128vdc
>> >1970 GE Elec-trak E15 36vdc
>> >1974 Avco New Idea 36vdc
>> >= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = 
= = = = 
>> >Cutting the space budget really restores my faith in 
humanity.  It 
>> >eliminates dreams, goals, and ideals and lets us get straight 
to the 
>> >business of hate, debauchery, and self-annihilation.
>> >
>> >                                -- Johnny Hart
>> >= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = 
= = = =
>> >
>> >
>> >
>> >
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