White/Blue LED Driver

[Jim Yanik]

Green fluorescents also have enormous efficiency. I remember 2 or even 4
times as good as white. They were used in copiers.

But I can't find the info on Google...


Thomas

Perhaps because they were not on all the time,but got only intermittent
use.(compared to standard lighting lamps)

 

[Zak]

I think you may need to check that last statement.

It _is_ what is used for LED LCD panel backlighting, it seems.


Thomas

 

[N. Thornton]

This is not a household bulb, it is a LED- notice the technology is
different.

I realise that. With a filament bulb the brightness varies to the
somethingth power of voltage - I cant remember off the top of my head
but its a big lot of variation. (13th power??) With LEDs there is
nothing like the same amount of variation with current, and one only
need drop a limited percentage of the supply V across the resistor to
gt about the same characteristic as a filament bulb, which is more
than satisfactorily stable.

If you were running off battery that extra Vdrop would matter to some
extent, but with a wall wart its basically a non issue.


Regards, NT

 

[N. Thornton]

I think you may need to check that last statement.

OK, it does depend. If comparing it to using one white LED then you're
right. If comparing it to using 2 or more white LEDs then what I said
would hold true.


Regards, NT

 

[Watson A.Name - Watt Sun]

I am intending to build a set of garden (path) lights from White/Blue LEDs
[not bulbs, due to power/life reasons].
What is the best method of driving these?
I was thinking along the lines of 555 Monostable driving 555 Astable to
produce narrow pulses, at a high frequency, so its not seen that they are
flashing, but it reduces the duty cycle.
Once the 555 Astable is built, how do i best drive the white / blue LEDs so
that not too much power is lost as heat.
LEDs will probably be in parallel, with one common cathode resistor going
to -ve/gnd

**Just use DC. In any event, be aware that white LEDs have a very definite
life span, due to their construction. Blue LEDs do not. I've used some white
LEDs, in my doorbell @ 20mA for 3 years. They're down to around 20% of their
original brightness. My preference, in white LEDs is with the Luxeon
devices. Superb spread of light and usefully bright. Very expensive,
however.

I find it odd that someone who has experienced reduction in light
output over time would recommend Luxeon star LEDs. They are running
at so much power that they would be even worse than the regular white
LEDs.

If there is a concern about phosphor degradation over time, then use
the light from red, green and blue LEDs combined to get white.

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[Trevor Wilson]

I find it odd that someone who has experienced reduction in light
output over time would recommend Luxeon star LEDs. They are running
at so much power that they would be even worse than the regular white
LEDs.

**The OP asked about white LEDs. The Luxeons are the most impressive, I've
ever seen. By a long margin. As for their life span, I understand that
Luxeon devices are at least as long lasting as any other white LED.

If there is a concern about phosphor degradation over time, then use
the light from red, green and blue LEDs combined to get white.

**Luxeons are also available in a range of colours.

 

[John Fields]

**Tell me more. AFAIK, they all use the same (at least similar) technology.
It is, of course, the fluorescent coating which fails, over time.

 

[Watson A.Name - Watt Sun]

**The OP asked about white LEDs. The Luxeons are the most impressive, I've
ever seen. By a long margin. As for their life span, I understand that
Luxeon devices are at least as long lasting as any other white LED.

Not if you don't keep them cool. And they _do_ get hot! I have
several and the heat is readily apparent after just a few minutes.

**Luxeons are also available in a range of colours.

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###Got a Question about ELECTRONICS? Check HERE First:###
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My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
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