Re: LED Questions (just two: )
- From: Peter Bennett <peterbb@xxxxxxxxxxxxxxxxx>
- Date: Sun, 15 Apr 2007 16:24:46 -0700
On 15 Apr 2007 14:51:52 -0700, "chull13@xxxxxxxxx" <chull13@xxxxxxxxx>
wrote:
Ok - since one person did offer here as a good place to ask some of my
ignorance to knowledge questions concering my LED Brake Light fantasy:
Ok, so I have learned that you vary voltage - preferable with pulse
width? - to vary the lunines output of an LED
LEDs should be driven from a current-limited supply,, not directly
from a fixed voltage. The most common way to do this is to connect a
resistor in series with the LED (or several LEDs), and connect the
combination across a fixed voltage supply.
The LEDs can be dimmed by pulsing the voltage.
AND that voltage drops from one LED to the next if wired in series
by say about 2 volts...
The voltage drop across an operating LED (red, yellow or green) is
about 2 volts (red a bit less, green a bit more)
1. Then would not the LEDs in a series be dimmer the further on the
series they are? (ie The 1st one brighter than the next with the last
being the dimest)
I know this must be wrong so
2. What am I missing?
The brightness of a LED depends on the current flowing through it, and
the current is the same at all points in a series circuit, so if you
have several identical LEDs in series, they will all get the same
current, and will all be the same brightness.
Thanks
(If you are so helpful to answer - just a link to info on the web
would be enough. Typing is a pain!! : )
--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
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