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[APD] Re: LED Lighting

> <snip, LED lighting comes up every six months,
> questions are the same, but the prices drop each
> time...>

Gee, whiz!  Check out the volume of posts for
It's double what was posted in November or October.

Time to wake up a thread from a couple weeks ago:
I've been going over the LED lighting issues, and
need help.  It looks like some smart people on this
list already have this information, and that we have
a good group of engineers and others with
sophisticated knowledge of available parts.

My intent:  Build an LED lighting system, initial
size for a 20g-40g tank.  The prices will become
increasingly affordable, but they are 'reasonable'
now (especially when you consider the setup costs
for a VHO/MH with electronic ballast).

There are numerous obvious advantages:

* more colors available (you physically can't fit many
  VHO/MH bulbs over small tanks or in a small area)
* more flexible/selective/granular spectrum control
  over specific tank biotypes or times of day
* more efficient lumens/watt
* long-life (no frequent bulb replacement)
* less/no color shift over the lamp operation
* safety (no more exploding bulbs)

Of course, there are disadvantages:

* LEDs are expensive (but with constant price drops)
* LEDs are directional (looking like little 'beams'
  of light, diffusers dramatically cut the light
  efficiency, so it might be best to have lots of
  very little ones instead of a few big ones)

Andy Lavery is apparently building one, and others
have/are trying to identify parts and do the same
thing (including me).  It would be nice if we could
share results.

First, LED selection:  Chris Ferrell identified the
Luxeon stars at 5500K, and those look good to me:

However, most of the LED spec sheets report in 
'wavelength', not 'color'.  And, by 'color' (what
we all know to be 5500K, 6500K, 10,000K, etc.), we're
talking about the 'temperature' as it pertains to
Plank's law of black body radiation, right?
That gives us a conversion from 'wavelength' to
'temperature'.  In theory, we should be able to
the LED spec sheets to our temperature terms.

There's a nice applet for this conversion at:


If you dial in "6740K", and press 'new', you get the
plot.  Then, press "Wien-Law' to get the maximum
displacement at ~4451.  Isn't that the same wavelength
(approximately) on the spec sheet for this blue
diode?  (Look to the peak of the wavelength graph
in the lower left corner).


Thus, I'd *like* to conclude that this blue diode
has a temperature of about 6740K.  That's a really
good temperature:  I personally like the 6500K lights
better than the 5500K lights (my plants grow better).
We *could* throw in a bunch of different LED
wavelengths, and ideally we would, but if I had to
pick a *single* color it would be at about 6500K.

However, I'm not happy with this conversion:  6500K
is still white, not blue (to the naked eye).  These
are blue LEDs.  We know you don't see lots of blue
until 10,000K-20,000K with our MH lights.

What's wrong with my conversion?  Who's found a 
6500K LED, and what was its wavelength?  (Worst case,
I'll just go to the Luxeon star at 5500K, but I don't
understand how to get the spec sheets into our 'temp'

Another issue is how to 'guestimate' the intensity
required, since LEDs are more efficient at lumens/watt
than VHO/MH.  However, that's an aside:  Unless anyone
has better ideas, I thought I'd shoot for 3w/g of LED
light (compared to our typical 2-4w/g for a 
moderate-to-low light tank), and I'll just dynamically
play with the number of lit LEDs on to see how many
watts it takes to get the same lumens as conventional
lighting (measuring with a lux meter).

So, (?) how do I get a good pile of LEDs, same or
different spectra?  Ideally, I'd have something like:

  Typical freshwater configuration:
  15%  5500K
  60%  6500K
  15%  8000K
  10%  far-red (for moonlight simulation)

  One kind of marine configuration:
  10%  6500K
  15%  8000K
  50%  10,000K
  15%  12,000K  
  10%  far-red (for moonlight simulation)

Of course, depending on how you load the LEDs and 
provide an interface for selective on/off (including
the total lumens you produce), a single board can be
used for both freshwater and a host of marine

As another issue, I'm concerned about burning out the
LEDs, (I want long life).  I'm still unclear on how to
drive these... is it the simple "for every 10 degree
increase you half the component life", or do you
fire at 50%/80%/95% Vmax, or do you fire at 100%
Vmax for *very* short periods of time, as was 
suggested here?  Yes, I understand 'clean' power
requirements, and will have a circuit board to
control that (probably driving the board with a
cheap wall transformer).

I'm a programmer and have no problem with bare-metal
and firmware interfacing.  The plan is for a computer
controlled interface.  I'm working with a very good
EE (friend hobbyist), and we can create circuits to do
anything (but we're still struggling with some of the
basics like LED selection, and don't understand all
the LED issues: We don't understand the comment made
where these 'white' LEDs are more 'fragile' than the
old 'red' LEDs, because the white ones are a hybrid
between LED and fluorescent lamp technology). 
Finally, we have (free) access to very expensive
fabrication technology for custom board layout, and
can iterate as many times as we want for whatever
configuration we want.  So, I'm not worried about
manufacturability of even 'zillions' of little

We also might also throw a couple sensor ports on the
board for measuring lux (nice feedback from within the
tank), and maybe pH and temerature too.

Of course, I'd be happy to report our results back to
this list (for free).  This is just a hobbyist
and we're not trying to make money or anything.  If
this works, though, we may be able to produce a pile
of boards to send to people on this list to try out.

Sorry for the long post.


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