GOALS:
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1. throw a hand-sized area of IR at 15-20 feet that can be **sensed** as heat using little energy.
2. i am only interested in energy thrown at a distance that can be sensed as heat. right now, collimated IR seems to be the way to go.
3. deliver about 5-10 mW/cm2
Ah, that helps...
Unfortunately, I only have one "ebay special" IR power LED, and don't have proper test equipment (or manufacturer's specs) to know what sort of output power, so I'm afraid I won't be much use on the practical specifics...
I do know Osram makes an 850nm PD
here which outputs 950 mW from a 1 mm^2 die, or 320mW/sr -- I can talk a bit about optics with respect to that, anyway. If you're looking at Chinese LEDs, they're probably lower output (for single-die), but you can pretty much scale it. That Osram emitter is about $10, though, so I'd probably go with it unless someone else can point you to something better.
IR LAMP DOESN'T HAVE RANGE. an IR heat lamp (e.g. a 250W) from GE prouces about 75 to 100W in front. i just need a measly 50-10mW/cm2 at 10-15 feet away. why don't i get this, even if i use lenses to concentrate the light outwards?
I've used heatlamps, but never had one apart (or scraped the red filter off, if that's even possible) -- I assume they're designed like a regular PAR30 flood beam; the light coming from the reflector is already messed up beyond fixing due to the lousy reflector of a PAR30 flood, and the light coming direct from the filament (which could otherwise be focused with a good lens) is probably going through the rippled front glass (which I assume is there...).
So I'm guessing that's the issue; if I'm wrong, and the front glass
is smooth, then you should be able to focus the filament to a parallelish beam with a lens, but the bigger the source, the bigger the lens needed. I'd guess around 1 foot diameter. And the ~75% of the light that goes by way of the reflector? wasted.
NARROW COLLIMATOR FOR LED? can anyone recommend a hi-power IR LED with a collimator that can do a 2-3 degree beam angle? the lowest i see are 15 or 20 degrees.
Well, I mentioned the best NIR LED I'm aware of above, so rolling with that... I'd tend to use an aspheric lens; let's consider a 4" diameter lens. You can figure that the LED's surface intensity fills the aperture, so we've got 320mW/sr, times the area ratio (2 in)^2*pi/(1 mm)^2, = 2500W/sr. At a range of 500cm, this is (2500W/sr)/(500cm)^2 = 10mW/cm^2 -- of course, after losses, it's less, but within your target of 5-10. The beam spread will be approximately 1mm/4in = 0.01r (0.6 degree), so at a range of 500cm, the 4 inch spreads by about 5cm, so something roughly like 6 inches across -- pretty much what you asked for.
So you should be doing something like a 100mm aspheric lens (optolife
has one, some people around the forums said their smaller lenses were good), or the same size reflector, if that's how you roll. You'll need to go bigger if your LED is less powerful, or has a larger emitting area. But see below -- I'm not sure 5-10mW/cm^2 is enough (but as I said, I can't run a practical test here -- if you're sure it's adequate, go ahead.)
840nm LD THROWS HEAT. personal experience shows a laser diode at 840nm, 300mW (input?) produces sensible heat in front (*not* waste heat at the die). Even at 15' away. It's a small dot, but it can be sensed and objectively shown as well (by using a thermal fabric that responds only to IR near human sensible range). i can provide detail on this if needed.
OK, laser diodes are rated by output, and typically have about 25% efficiency IIRC -- if 300mW is the input, it would be perhaps 75mW output, but since you put that ? there, I'm assuming it's 300mW output.
As you say, it's a small dot -- I expect no more than 1 cm^2 at that range, although it depends on your optics -- so even if 300mW is the input, it's 10 times your target of 5-10mW/cm^2, and if 300mW output, more like 50x. Are you sure 10mW/cm^2 is really enough?
If you do need to get to 100 mW/cm^2, then you're looking at a minimum of 12" aperture with any IR LED I know of... maybe someone who does more IR stuff knows something better than the Osram emitter I'm looking at.
[...]
FOLLOWSPOT THROWS HEAT. a followspot (spotlight) at 750+W and an airplane landing light at 150W (spherical reflector, BIG) are able to produce light & heat that can be sensed at about 8' away.
Yep, I got a Q4509 ACL in a 6V lantern housing -- it was actually the first thing that came to mind when I read your requirements list above! But then you said "using little energy", and I'm afraid a 100W halogen running about 140W isn't quite it.
HID GOOD BUT CAN BURN. videos of high intensity discharge flashlights on youtube show that there's enough power to burn cardboard with a simple biconvex lens. so this should be able to throw good heat, though the possibility of burning a sofa keeps me from thinking of this as a solution.
Note that that's focusing it down to a point -- if you focus it to a parallel beam (as near as you can get), burning things will be less of a problem. HID (especially short-arc) with a high quality reflector (parabolic, or elliptical reflector + aspheric lens) is probably the most compact hot-sensation transmitter you can make. The bigger concern with HID (and it's not really a problem, as long as you deal with it) is to make sure there's a sheet of UV-blocking glass in there somewhere, as they deliver a hefty dose that can cause rapid sunburns and serious eye damage.