RE: LED lighting for garden

["Keith Doxey" <ukha.diyha@xxxxxxx>]

Hi Ian,

I didnt fully read the earlier posts regarding the intended use, but I
assume this is just for a decorative effect rather than illumination. These
LED's are extremely bright but have a VERY narrow viewing angle, some less
than 20 degrees.

On axis they will give a painfully bright light similar to a laser beam
catching your eye in a nightclub. They will shine a beam of light over
quite
a large distance putting a spot of light on the surface they hit. As you
move off axis they very quickly appear not to be lit.

You are correct about the numbers....White and Blue LEDs have a much higher
forward voltage. You could always use a 24V supply. That is also perfectly
safe, in fact most outdoor Xmas light sets are 24V with 10 x 2.4V bulbs in
series.

With LED's you MUST have a resistor to limit the maximum current throught
them to a safe value. Taking the White LED's on the page you mention,
Forward voltage @ 20mA is 3.6V so placing several in series would add up as
follows 3.6, 7.2, 10.8 (limit for a 12v supply) 14.4, 18v, 21.6 (limit for
24V supply). 3 LEDs on 12V needs a 60 ohm resistor to drop the excess 1.2V
nearest standard value is 62R. 6 LED's on 24V needs a 120 ohm resistor
(standard value)
Power rating should be 0.6W Metal Film Resistor

HTH

Keith

-----Original Message-----
From: Ian Oliver [mailto:ioliver.lists@xxxxxxx]
Sent: 19 April 2001 09:44
To: ukha_d@xxxxxxx
Subject: Re: [ukha_d] LED lighting for garden


In article <000d01c0c85a$f93fe560$de7f9284@xxxxxxx>, Keith
Doxey wrote:
> If you put the 5 LED's in series they would require 10V leaving the
resistor
> to drop 2V, a 100R resistor would give you the same number of LED's
lit at
> the same brightness with a total consumption of only 20mA and only 17%
of
> the power lost in the resistor.

I'm looking at using modules ultra-bright LEDs as at
http://www.theledlight.com/led-specs.html
 I think you can just connect
three
across 12V, though other blurb mentions resistors. I guess these are for
the
red/orange stuff with a lower forward voltage.


Regards

Ian Oliver
Sunny Leeds, UK
Using Java on Tini for control via Dallas 1-wire






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