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Unread 02/03/2015, 08:09 PM   #26
zachts
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Quote:
Originally Posted by Fredfish View Post
Its a little off topic, but I'm curious to know how you figured out the efficiency of the emitters.
....its on the data sheets. 30% is typical for latest gen LEDs at rated currents. Drop the current down and 40% plus is attainable form at least Cree and Luxeon......


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Unread 02/03/2015, 08:45 PM   #27
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....its on the data sheets. 30% is typical for latest gen LEDs at rated currents. Drop the current down and 40% plus is attainable form at least Cree and Luxeon......
Either I'm looking at the wrong data sheets or I have no clue how to read them, always a possibility. Royal blue and red show radiant flux which is what I thought you needed to calculate efficiency. Everything else is shown as luminous flux. from which you can't calculate efficiency. What am I missing?


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Unread 02/03/2015, 08:49 PM   #28
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White LEDs are also effectively royal blue LEDs, but with the phosphor added. Of course the conversion is not going to be 100% (from what I've been reading, about a 10% Stokes shift loss), so a white is somewhat less efficient in radiated energy vs a similar generation royal blue.

(Note my 30/40% numbers are ballparked, its worth noting that green LEDs and cyan LEDs are less efficient than most others at this point in time)


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Last edited by theatrus; 02/03/2015 at 08:55 PM.
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Unread 02/03/2015, 09:01 PM   #29
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Originally Posted by theatrus View Post
White LEDs are also effectively royal blue LEDs, but with the phosphor added. Of course the conversion is not going to be 100% (from what I've been reading, about a 10% Stokes shift loss), so a white is somewhat less efficient in radiated energy vs a similar generation royal blue.

(Note my 30/40% numbers are ballparked, its worth noting that green LEDs and cyan LEDs are less efficient than most others at this point in time)
That's the number I was looking for. Just figured out what stokes shift was a few days ago, but did not see anything on what sort of energy loss there was.

Do you not also need to figure in the loss for internal reflectance of the phosphor? That's another ~20% if my (failing) memory serves me.


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Unread 02/03/2015, 09:03 PM   #30
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Quote:
Originally Posted by Fredfish View Post
That's the number I was looking for. Just figured out what stokes shift was a few days ago, but did not see anything on what sort of energy loss there was.

Do you not also need to figure in the loss for internal reflectance of the phosphor? That's another ~20% if my (failing) memory serves me.
You would, I'm not sure of how much is going to bounce back (and how much of that is pure loss). I do wish this was a more direct data sheet spec, instead of lumens/W :-)


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Unread 02/03/2015, 09:18 PM   #31
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I found a study by Phillips the other day comparing remote phosphors to to direct coating phosphors. That's where I got the 20% (I think) number from. Unfortunately I did not save a link and my memory for these things is not very reliable.

Yes, it would be nice if there were a more direct data sheet, but then I would sleep more and read less and where is the fun in that.

Edit: Sigh. It was a Cree paper, and the 20% was the lumen output gain from the remote phosphor. They mention internal reflection loss, but do not put any numbers to it.


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Last edited by Fredfish; 02/03/2015 at 09:32 PM.
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Unread 02/03/2015, 10:40 PM   #32
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The simpler way to look at it is how many watts of heat is being generated vs how many watts are being fed to the LED (still not all of the equation though but between stokes shift and that is enough to make my head hurt when trying to account for the rest)........most of what isn't lost to heat is emitted as the useful light we are after, not all, but most of what's not accounted for as heat.....


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Unread 02/03/2015, 10:43 PM   #33
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I found a study by Phillips the other day comparing remote phosphors to to direct coating phosphors. That's where I got the 20% (I think) number from. Unfortunately I did not save a link and my memory for these things is not very reliable.

Yes, it would be nice if there were a more direct data sheet, but then I would sleep more and read less and where is the fun in that.

Edit: Sigh. It was a Cree paper, and the 20% was the lumen output gain from the remote phosphor. They mention internal reflection loss, but do not put any numbers to it.
Remote phosphor is pretty cool and gains in efficiency over comparable white LEDs with phosphor on board if the design of the reflector array allows the blue light to be reflected back to the phosphor over and over again instead of being absorbed and turned directly into heat........

Very cool technology that I hope will soon hit the reef market since it's far cheaper to make a remote phosphor coated lens tuned to emit reef specific light than it would be to make an LED with the phosphor on board which requires much more specialized manufacturing......

oh, well, enough side tracking.




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Unread 02/03/2015, 10:59 PM   #34
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Theatrus.

Where did you get the MCPCB's manufactured at? Got a link? Thanks!


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Unread 02/03/2015, 11:48 PM   #35
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Theatrus.

Where did you get the MCPCB's manufactured at? Got a link? Thanks!
I have a list of various PCB outfits which I've used for various reasons (with varying levels of English skills), but for these I ended up being lazy and simply using http://www.goldphoenixpcb.com


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Unread 02/04/2015, 04:01 PM   #36
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...

oh, well, enough side tracking.

Agreed. Thanks for the answers folks.

theatrus. I'm looking forward to the finished product. Its fun when someone does something different.


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Unread 02/04/2015, 04:48 PM   #37
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I'm relatively terrible with precision in the machine tool arts, but I did find a few spare cycles to drill and tap the heatsink:




The four corners will be replaced with nuts and threaded rods, but for testing the LED board energized screws will do nicely. All screws are M4x0.7 (yes, I went metric).

Now it has the "brick" form factor


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Unread 02/04/2015, 09:32 PM   #38
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Alright, found some time this evening and did the first emitter brick build!

Step 1: Stencil the PCB:



Step 2: Place parts:



Step 3: Since this board is a great heat conductor, I opted for just tossing it in my Reflow Skillet™ (Hamilton beach large skillet, c/o Amazon. Flat bottom!). The astute reader will notice my cyan channel is outright missing - which is correct, I forgot to order that. Welp. Maybe I'll carefully tack in something else on the Rebel footprint later (Warm whites?)



Success!



(not pictured, a bunch of probing, and realizing the top-right UV LED (of the very spendy 405-410nm bin, is shorted at the pad. I futzed with it some, but decided to press on anyway - its likely a PCB short I didn't see and cut away)

I started building the cable harness (got better as time went on) and tested each channel at 10mA from the bench supply:



Left to right, my wiring was improving. This is a nice silicone jacket 24AWG stranded.



Cool White




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Unread 02/04/2015, 09:33 PM   #39
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Deep/Royal Blue



Blue (windex blue) (485nm)



Red



PC Amber



Cyan (not pictured )

Green




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Unread 02/04/2015, 11:09 PM   #40
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That's a lot of green. Are you going to put optics?


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Unread 02/04/2015, 11:12 PM   #41
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No optics (most won't fit). I have 9 more boards after this one and will likely play with different color mixes, I'm not settled on this arrangement.


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Unread 02/05/2015, 12:39 AM   #42
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not to shabby at all!


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Unread 02/05/2015, 06:52 AM   #43
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Very nice

Tim


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Unread 02/05/2015, 01:50 PM   #44
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Looks real nice. Could you explain the part with the stencil? Are you applying solder paste?


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Unread 02/05/2015, 02:14 PM   #45
theatrus
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Looks real nice. Could you explain the part with the stencil? Are you applying solder paste?
Yup.

The stencil is a kapton one from OSHStencils.com. Build a frame for the board (old PCBs, these little acrylic frames, etc), tape it down, align, and then use a putty knife to "print" the stencil by simply applying a squeegee like action. In this case I used a (very expired, like 5 years out of date ) jar of Kester SAC305+EM907 paste. Lift the stencil up carefully, and then just use tweezers to place parts on top of the paste.

I may have one cold thermal pad on my board I may have to touch up after running some thermal tests. More on that later.


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Unread 02/05/2015, 04:36 PM   #46
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Running some thermal and output tests using three channels running at design-maximum output (750mA). I'm also monitoring PAR output using a Apogee PAR sensor (multiple: x5). There is no thermal paste or other gap-filler material between the PCB and the heatsink, as a baseline measurement.



PAR sensor, at 6 inches, centered. Don't consider this absolute, its mainly to check for thermal-related output reduction.



Output levels, holding steady for 30 minutes so far:



Thermals.

No fan, two channels running. The top-right royal blue has the highest measurable temperature from the (hacked to 320x240) FLIR-E4. This is a close approximate of die temperature - IR is going to be limited by the silicone lens of course.

Note that shiny aluminum heatsinks are not directly measurable using IR - in later images I've placed pieces of black electrical tape over sections of the heatsink to provide a better radiator. Ambient is approximately 18C in all of these images.



Three channels operating - sorry about the funny angle, I had already setup the PAR test at this point. Low-CFM Panaflo is running at 9V (basically inaudible)



Side of the heatsink with electrical tape to get a temperature read.




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Unread 02/05/2015, 05:22 PM   #47
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What are U1 and C1 for????
nice toys btw..


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Unread 02/05/2015, 05:32 PM   #48
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What are U1 and C1 for????
nice toys btw..
U1 is an MCP9808 I2C digital temp sensor, C1 is the bypass cap for it.

Been building the lab up over many years, with some very very lucky finds (such as the "shows ERR, must be broken" 3458A which just needed new backup batteries )


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Unread 02/05/2015, 06:26 PM   #49
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Been building the lab up over many years, with some very very lucky finds (such as the "shows ERR, must be broken" 3458A which just needed new backup batteries )
Love when that happens..
BTW: A toy you need..

I would think it could, w/ the proper programming do "par"
Of course it also needs a remote sensor..


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Unread 02/05/2015, 06:37 PM   #50
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Don't tempt me! [empties wallet]


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