led lights

[david1701]

hey guys i'm thinking of making something along the ideas of this http://brainerror.net/texts/howto/macroring/

but scaled up and crossed with this

http://www.diyphotography.net/studio...ld-a-ringlight

so i intend on using very powerful led's (these http://www.rapidonline.com/Electroni...s/78767/kw/led are the brightest i can acquire) and mounting them in 4 alternating rings of 9 (or possibly non alternating rings of 18 - bot colours not just one) which will give 36 (or 72) LED's which should be fairly bright

each ring is to be wired as 9 (or 18) parallel leds each with a series resistor (about 140 ohm)

with the rings in parallel to each other and switched individually (as i have no idea about brightness)

just wondering if any wiser heads had any thoughts to add

David

(just a thought i use a dslr so its not gonna be a silly looking huge ring on a little compact cam )

[david1701]

had some feedback from photography guys about potential brightness and they have doubts anyone know of a way of doing this without using heatsinks which would make it v ungainly

[David Sparkes]

http://brainerror.net/texts/howto/macroring/

http://www.diyphotography.net/studio...ld-a-ringlight

http://www.rapidonline.com/Electroni...s/78767/kw/led

Neither the second or third links function as you desire. They both bring up error pages.

-------------

requested project not found

sorry,

Looks like there is no project like you are looking for.

------------

and

---------------------

Looking for something on Rapidonline.com?

The page you are attempting to access does not exist. You may have followed an outdated link

--------------------

[sotal]

I think these are what the links should have been:

http://www.rapidonline.com/Electronic-Comp...Ds/78767/kw/led

http://www.diyphotography.net/studio-light...ild-a-ringlight

[david1701]

yep those are the links, so sorry they were duds

[TheRecklessEngineer]

Assuming you are using 36 LEDs, and each one is 30mA, you will need a PSU that will kick out (0.03*36)=1.08A. Nothing too hard there.

Rather than having a resistor for each LED, I would have a single resistor for each bank of 9. You can also avoid the need for a heatsink if you use a PSU with an output voltage close to that of the forward voltage of the LEDs (from the technical info...3.3v)

So, assuming you use a 5v supply (closest one that should be easily available) and running 9 in parallel, you will need (5-3.3)/(0.03*9)=6.3 ohms for each ring of 9.

The power dissipated by the resistor will be (5-3.3)*(0.03*9)=0.459 Watts.

So use a 6ish ohm resistor rated at 1/2W and all should be peachy - you won't need a heatsink to dissipate this amount of power.

Or, if you can get one, use a supply that kicks out 3.3v and don't use a resistor!

(By contrast, if you use a 12v supply, the resistor will be dissipating over 2W - you'll need a heatsink then...especially if you think you will be running 4 of the things.)

[TheRecklessEngineer]

Another thought just occurred to me - if you put each ring of 9 LEDs in series and use a 30v PSU - no resistors needed.

[pete3000]

I would have a look on e-bay and save yourself a small fortune in time and money . Search for

led ufo light. or

led camping light.

I pay around a fiver runs off 4AA alkaline batteries. (don't use high power nicads, no current limit, burns them out quickly)

these come with 24/48/36 leds and are really useful when camping or repairing as they have a low profile and can be stuck with a magnet, hung up or on a screw.

Pete

[david1701]

cheers for the help guys, but i'm gonna abandon this one as i have talked to photography guys and they doubt i will get enough light for anything but macro work, and i don't really do macro work.

But thanks for all the info,

David