QUOTE (videotalk19 @ Nov 29 2007, 11:20 AM)
hi Sudu
I have a projector and I am using 15 inches screen. and its about 12x10 inches in size. In that size I think I can only fit approx 30x25 leds at 10mm. next talk about series and parallel. As I told you that I dont know much but I was talking to my dad and one other guy and now I have a good idea about series and parallel so I think thats what I will do. As far as supply is concern, I am here in computer business and I have plenty of power supplies and other kind of supplies. Even if it is different one, I can get any, once I see it what I need.
Now about dedicated pcb or general pcb. you would know better since you have been through all this. If you think that I will need cooling for the array, and dedicated pcb in better for that then I will go for dedicated pcb. unless its very hard to make one. you mentioned about single or dual layer stack. first of all I never seen a dual layer stack but I knew that 10mm leds would have some space left in them. So again if dual layer isn't hard to make then I will go for dual layer. About the shapes, I didnt get you mean by bullet. what I have seen are the regular leds which are round on the top. and I have seen some which are flat on the top but they are actually very rare. so if you mean bullet by round on the top then thats what I will get.
Last but not the least, the Angles. you said that most out there at 130,000mcd are at 50 degrees, the ones I have seen so far are only 12 degree for 10mm. You mention about being careful choosing low angles around 15 to 30. Is it good to have low angle or bad. because I am reading two different opinions about it. some people say that try to get as small angle possible as could and some say get the wider angle so that light would blend in and you don't have to move led panel too far from lcd. now you have first hand exprience and could you tell me what is best you found. because at 10mm led size there are mostly 12 degree angles. at 5mm we could easily get 20 to 25 degree angles. Here I am sending you a link about angles, accroding to this guy, wider the angle better the blend is and less the spots are.
http://www.lumenlab.com/forums/index.php?s...=9136&st=60if thats the case then 5mm is the way to go because 10mm only gives 12 degree. But with 5mm, most light intensity we can get is around 40,000 mcd. which is still not bad considering you are using only 20,000mcd. I just calculated lumens on this calculator a minute ago and the result looks better with 5mm. And also if wider angle blends the light more then 5mm should be the choice.
http://led.linear1.org/lumen.wiz5mm at 40,000mcd with 20deg angle of 1500 leds will produce 5727 lumens. becuase of wide angle.
10mm at 130,000mcd with 12deg angle of 750 leds will produce 3356 lumens. because of narrow angle.
I will conclude my reply here. lets see what do you think about it.
Please let me know what I need and I will start buying the stuff. I will need your help every step of the way but I am a very quick learner so if you guide me through I will be able to do it in no time. Sometimes its better to learn from someone else experiences than going through it.
thanks
bye
P.S: if you think that 5mm of 1500 is the way to go then I think that above we discussed about heatsink and dual layer stack, that wouldn't be required would it?
ok. Let me try to ans one by one.
LED angle - u are right about the 12deg 130000 10mm leds. Now if u use 15deg or lower leds the LCD pannel should be atleast 20 to 25 cm away from the leds to avoid patching. If u use higher upto 30deg leds the distance reduces to about 15cms. Using more deg leds won't help much as most of the light is waisted and placing leds too close to the lcd results in the image of the leds being projected buy the triplet
I personally use 5mm to would suggest 5mm single stack...but cooling is still required as the pannel generates lot of heat ...so a dedicated pcd helps a lot. How diff. pcb making depends on the available resources......first u need a pcd designing tool like orcad or protel or any other free pcb tool then u need a professional pcb maker around ( who is ready to make a few pieces ) to whom u can give the gerber files of your designed pcb and he will make the pcb from that gerber data or u can buy copper clad and drill 3000 pin sized holes ( not recomended ) or u can buy from someone on the site who has some leftovers
The general purpose pcb i made powers 25 led in serise with 560E and 70 such serise in parallel using a supply of 90Volts and the whole module draws about 1.7amps. You being a computer guy would be having supplies of lesser voltage but of higher current ratings i.e. 12v/12 amps or 12v/17amps etc..for this kind of power supplies u need to put 3 or 4 leds in serise + limiting resistors and for 1500 leds u need 1500/3 or 1500/4 such serise connected leds in parrallel. each led drops about 2.5v to 3.3 volts depending on its make(see datasheet). Remember to read the I max rating and never go very near to the limit....for a 20mA i max don't cross 15mA...or the life of the led would be reduced significantly.....though u will get more brightness but don't get temted to push higher currents even if u have tested a few leds from the same lot separately with higher currents........in a large pannel heat is what kills the leds...and cooling is not that uniform as it may appear with general purpose boards.....with dedicated pcbs u can have upto 15mA of current but no higher.......
about the bullet shaped leds -- if u see the led side on the shape of the front is more of a elips rather than of a semi circle. The elips lens focuses light better and leaves space for the botton stack better than the round. its a bit exp than the round one.
We all r here to help...just ask..
FOCAL LENGTH : f = 216mm&343mm
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....but gives nice pictures 
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to squze in more light from more leds but within the same space that is with a 14.1" or 15" monitor...