Yep, they do flash so as to increase the percieved brightness by driving the
LED to a brighter output in the 50% on cycle while avoiding some of the
heat build up with the off cycle. But, I always thought that was at more
than 100 Hz where the on-off flashing would not be perceivable - at least by
the majority of the population. I can't perceive the 'dotted streaks' you
speak of.

Just curious, Paul. What was the lowest computer CRT monitor refresh rate
you can live with? (The new CFL backlit LCD's don't flash.)

Bill Daniels


"Paul Hanson" wrote in message
...
About the flashing. I am not referring to any mode
of load applied to the lights (like putting on your
hazzards, or using a turn signal), I am talking about
the light cluster units themselves.
Not all LED lights for vehicles are created equal.

A great deal of them do NOT light up like an incandescent
bulb. In fact, most of them I have seen do not. Most
have a little circuit board in them, which aside from
regulating voltage, dictate how many flashes per second
they have while engaged in different modes.
Yes, in the US a lot of buses/trucks/etc have LEDs,
which IS clearly a superior technology, if properly
designed. Unfortunately a great deal (not all mind
you) of them DO possess what I call the 'strobe effect',
for lack of a better term, I am harping on. This effect
happens while they fully on (constant voltage), since
they are set to flash say, oh maybe...40-200 times
per second, which appears to be on like an incandescent
at a steady glance, but not when you run your eyes
across it while it is stationary. I have spent a LOT
of time on the road, particularly at night and I can
assure you that many of the vehicles equipped with
LEDs are using a type that has this highly distractive
circuit built into them. I fully agree that LED's are
the way to go, all I am saying is please, on behalf
of all others on the road including me, buy good ones
that either flash so quickly that it is undetectable,
or do not flash at all like an incandescent. There
are many types available, all you have to do before
buying one, is turn it on (apply the voltage), then
move your eyes across it quickly. Does it make a solid
red streak, or did it leave the imprint of a dotted
line? Flashing lights are distracting, thats all. A
little homework goes a long way, with any purchase.
Here are a few links to other discussions about this
very same phenomenon that I now realize plagues many
more people than myself: (Granted it is a UK forum,
but it touches on the same effect, and if you want
I'm sure I can find more and from the US)

http://www.safespeed.org.uk/forum/vi...8808&highlight
=#118808

http://www.safespeed.org.uk/forum/vi...539&postdays=0
&postorder=asc&start=0

Glad you guys just happened to get LEDs that work well,
and I agree, the third brake light is indeed a good
idea.

Paul Hanson



At 23:12 10 July 2007, Bumper wrote:
Eric,

I couldn't figure the 'flashing' comment either, unless
he was referring to
what sometimes happens with a non-electronic flasher
without enough
load - - e.g. if you replace your turn signal incandescent
lights with LED
units, the load won't be enough to operate the OEM
flasher. This can be
corrected by either installing a suitable electronic
flasher or by
installing a load resister in parallel with both turn
signals.

Also good is to install a 3rd brake light at the top
of the trailer fin. It
may be necessary to make a wedge or bracket so that
the LED fixture is
perpendicular to the ground (LED's used in these fixtures
have a relatively
narrow beam angle as compared to incandescent lights).
A relay is used for
the 'logic' circuit with the coil driven by one turn
signal and the NO
contact connected to the other. Both turn/brake lights
on together, then the
3rd brake light works.

Newer Cobra trailers have a bigger tail light fixture
installed semi-flush.
A shame, since it's still not good quality and the
larger hole in the
trailer means you can't use standard round truck LED
lights easily.

I used Maxxima LED fixtures on my trailer, reasonable
price and good
quality.

bumper


'Eric Greenwell' wrote in message
news:7BTki.9017$ZO4.6321@trndny05...
Paul Hanson wrote:

I don't remember (at least recently anyways) seeing
a thread about LED lights for trailers. However, I
think LED's are a great idea, BUT... I just urge anyone
buying them to look into the flash rate (they are
constantly
blinking as opposed to solidly on like incandescents)
of lights you are investigating and choose the highest
rate possible. Reason being, it is VERY annoying and
distracting to be driving at night, and to have a
set
of very bright taillights 'strobe' a dotted line across
your vision as you scan your eye across them. The
lower
the flash rate, the more exaggerated the problem is.
I am very surprised DOT has not set some kind of minimum
standards as to flash rate (as well as better guidelines
to headlight lumen maximum/spectrum range, anyone
else
hate those ultra-bright purple blue headlights?).
Remember, if it is distracting to other drivers, you
are increasing your chances of an accident as opposed
to promoting safety so please do your homework before
purchasing.

There are plenty of places selling brake/turn/running
light units using
LEDs that display exactly as the incandescent units
do (no
flashing/strobing, just on or off). In the USA, LED
lights are very
common on all sizes of trucks and buses, and none of
them flash.



"Do the usual, unusually well"--Len Niemi