I am detecting a projectile by detecting a change in radiant energy into 
a lense/phototransistor system.

These are sometimes used indoors and when they are, an artificial light 
source is needed.

We currently have an incandescent light source; I am making a LED light 
source.

I created a unit using red LEDs with a 630 nm "dominant" wavelength; it 
works well.

But it is visible and may be distracting in the app, so I would like to 
try IREDs.

I hadn't thought about the wavelength of the phototransistor; thanks for 
that. It turns out it's optimized for 940nm, so the red LEDs are 
considerably off of that desired wavelength; that tells me that perhaps 
a IRED at the right wavelength could be a lot "dimmer" than the red LEDs 
I'm using and still work well.

There is no sensitivity vs wavelength graph on the datasheet; it's 
really meant to be used at 940 nm. However, it has worked well in the 
app with the incandescent for many years/units.

I figured visible LEDs should be able to be rated in the same way as 
IREDs, since the mw/sr is a more generic term, but do not know how to 
figure out mw/sr given typical datasheet info for visible LEDs.

I do have a way to test change in current through the phototransistor 
with a given emitter system; I guess I'll just have to try that; I was 
just trying to figure out if I'm even close to what I might need before 
I go sampling 60 IREDs.

Thanks for the input; as always, it's appreciated.

Mark

Mike Hord wrote:
> [SNIP]
> Maybe if you told us more about the application...
>
> Mike H.
>   
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