Pedro,
If I remember
correctly
The viewing angle should be stated as
the point where the light output is half (they usually quote full angle
rather than half angle).
If you look directly (head on) at the LED, you can move
30 degrees in any direction before the light output drops t half the
level compared to looking head on at it.
You WILL need to limit the current t about 20mA
(approx2/3 max) through each diode by using resistors
ie
12v supply- 5.5v across LED = 6.5v
dropped across resistor
R= 6.5v/20mA = 325ohms
(330 is close enough and an available value)1/4 watt resistors will be
OK
You could arrange t feed all LED's in a parallel array
through a single higher wattage resistor, but if(as) any LED fails, the
current through the rest will increase. This would not be a problem if
you have a large array and only one or two fail. But if you only had say
2 in the array and one failed the current would blow the remaining one
also.
One final point. The light output from these are quite
low so you would need quite a few to illuminate something,
http://uk1.farnell.com/Search/search4-frame.jhtml?_DARGS=%2Fcommon%2Fprodsearchform.jhtml
list some much brighter ones, narrower angle, but if
your using an array...
John
-----Original Message-----
From:
Pedro de Oliveira [mailto:oliveirp@xxxxxxx]
Sent: 25 July 2001 08:53
To: HA
(E-mail)
Subject: [ukha_d] OT - LED's
I thought I would try this question here first since
someone is always
willing t help with their
expert advice... Anyway....
I am looking at buying some LED's t brighten up a small
area and have been
stumped by their
specifications and their meaning. I understand most of it
but what does viewing angle mean ? I though an LED
emitted light all around
but then I found specs
at Maplins and these have a viewing angle mentioned
http://www.maplin.co.uk/products/frameres.tpl?partcode=JA24B:JA25C:&SKU=12703&cart=943432253&d=f&max=1&Group1=LED%205mm%20blue.
I would like to use a 12v supply but does this mean
because they are rated
at 5.5v max that I would
need two parallel rows of LED's with a resistor and
if so how would I wire them so they don't "pop" every week
?
Cheers in advance
pedro
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