At first, I was inclined to go for the “P” version for two main reasons:
1) Better coupling with the acrylic sides cause of the flat head, allowing for a more robust and neat design.
2) Twice as wide half-angle, which in theory would spread out the rays more evenly inside the acrylic.

But then, I saw some people raising attention to the “radiant intensity” spec as being of high importance for the brilliance of blobs. Then I went back and compared the specs for the “P” and “P-less” versions, and what I found was this:

- SFH485
Radiant intensity (If = 100 mA, tp = 20 ms): 25 (Ie min) - 160 (Ie max) mW/Sr
Radiant intensity (If = 1 A, tp = 100 μs): 300 (Ie typ) mW/Sr

- SFH485P
Radiant intensity (If = 100 mA, tp = 20 ms): 3.15 (Ie min) - 6.3 (Ie max) mW/Sr
Radiant intensity (If = 1 A, tp = 100 μs): 48 (Ie typ) mW/Sr

I really have no idea on what all these letters mean, but it’s quite clear that the numbers of the “P-less” version look better. Would it be because of the wider half angle, or even the flat head of the “P”? Does it make the 485P an inferior led for FTIR?

The thing is I have to import this component, bringing its costs way up cause of delivery and import taxes. So I’d rather not risk making the wrong choice. Tks.

They both seem to work fine according to the forum members. I myself have already ordered the wrong IR LEDs (*sigh*) which had an RI (Radiant Intensity) of 35 mW/sr, which I heard was too weak. As you can see in your post the P version had got 3.15 - 6.3 mW/sr (forget about the 48 mW/sr) and so I would say it is waaay too weak, but somehow they seem to work fine. I really still don’t have a clue why they do though and why mine probbably won’t work..

Has any one tested both of them? Which one is better for DI / DSI ?

SFH485
Radiant intensity (If = 100 mA, tp = 20 ms): 25 (Ie min) - 160 (Ie max) mW/Sr
Radiant intensity (If = 1 A, tp = 100 μs): 300 (Ie typ) mW/Sr

(If = 100 mA, tp = 20 ms)

If tp>>20ms IR-LED cannot have the problem ???

I did test the 485P against the 485-2, but only for FTIR. I found the 485P to be a little better because of the wider angle, which I think could also help for DI.

In fact, the 485 and 485P seem to be the very same diode, but with different lens. That accounts for the wider angle of the “P” and also for the huge difference in radiant intensity, but it seems the angle is more important than the radiant intensity according to my tests.

GFantini - 18 August 2008 01:41 PM

I did test the 485P against the 485-2, but only for FTIR. I found the 485P to be a little better because of the wider angle, which I think could also help for DI.

In fact, the 485 and 485P seem to be the very same diode, but with different lens. That accounts for the wider angle of the “P” and also for the huge difference in radiant intensity, but it seems the angle is more important than the radiant intensity according to my tests.

So would you now recommend the SFH 485 or the SFH 485-P ?
sounds like because of the wider angle it has a lesser power but at the end it comes out for the same? maybe even better blobs for the P-version?

That depends on your table’s engineering. The “P” is just easier to implement, because you can simply place it flat on your acrylic’s edges.

You might get brighter blobs with the regular SFH 485, but in order for that to happen you should place the leds at angle of about 35 degrees with your acrylic’s edges, which makes your setup a little harder to build.

In fact, both leds are equally powerfull, but because the “P” has a wider angle, the beam gets more dispersed, thus lowering its radiant intensity.

I would go with SHF 485P they have a larger angle with is better for FTIR.... but since they have lower luminosity i would put at least 1 per inch and on all 4 sides

There is also SFH 487-P. It has 65 degrees angle. Does anyone tryied it?

I’ve been having a lot of problems with the P series, I did some test’s and noticed that the ball of light coming out of the P is smaller but is detected at a wider angle, 80 degrees from horizontal to be exact it seems to be visible from a longer distance as well, whilst your non P LEDS appear to be brighter but don’t travel as far and disapear from vision at 40 degrees or there about from horizontal, Im wondering if any one has had any success with the P’s as they are giving me headaches they should be working a lot better then they are but at the moment i’m stuck with a pretty poorly lit array. Has anyone built a large LED array with the SFH 485P’s? Im wondering if these lights work better for smaller touchscreen’s then bigger ones.

Hey JayBee,
I heard that a lot of people use the 485P version
I orderd some of those for my 30 x 40 cm Touchscreen
I haven’t build it yet, because there was an ordering mistake and at the moment i just have 20 LEDs which is a little less, so i wait for some more.
So yea ... I guess because a lot of poeple use the P version, there shouldn’t be a big problem with it ... Maybe you took a too big distance between the LEDs

If you have more questions just PM me
Splash_5