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What you should be looking for is a high power IR led with a relatively wide beam width.
A 10W IR LED will probably produce 1W of IR. Placed in a hexagonal pattern about 3.5cm between centres, and used at a distance such that the beam covers at least a 4cm diameter circle (2cotθ where θ is the half angle) should yield about 100mW/cm^2
Each of these LEDs will be dissipating 9W of heat. You will require either a huge passive heatsink, forced air cooling, or possibly liquid cooling depending be size of your array.
The smallest battery you could likely use would be a car battery and I would strongly recommend switch mode constant current drivers.
Oh, and wear glasses that don't pass IR if you value your eyesight.
(Run them at half power to get 50mW/cm^2)
Well, 50mW/cm2 over 20cm2 is 1W. Given the approx radiant efficiency of IR LEDs appears to be in the order of 10%, you need 10W of LEDs.
You can do that with less than a car battery (my earlier estimate was for about 200cm2)
I would suggest that people may be designing things like this using the only power rather than the radiant power.
Well, you could try a TSHG5510-ND from Digikey. It has a wide angle, emits 55mW at 100mA at a Vf between 1.5V and 1.7V. the peak emission is at 830nm.
These are about $1.50 each and would be good for about 1cm^2. You would require 20 of them with a total input power of around 3.2W. Because of the wide beam width, you could place them as close as 1cm from your skin. The wide beam width would also make them far more eye-safe.
The LEDs are far more efficient than others you've found.
Because you're running them very near their maximum power, you would want to use a constant current driver (or 2).
Two strings of ten LEDs would require a little more than 20V at 200mA. 10 AA cells in series would be a reasonable power source. A switch mode (as opposed to linear) constant current source would probably extend your battery life by around 25%
Looking up the Energizer E91 datasheet, you would expect a run time of about 3 hours with a linear regulator, and around 4.5 hours with a switch mode regulator. The difference is more than I estimated above because the power you can get out of the batteries increases significantly as the current you draw is lowered.
If you run it from a plugpack, you could probably get away with something rated for 24V at 500mA or more (go for 1A). A simple linear current regulator (one for each string) would probably be fine because you don't have to worry so much about efficiency.
Sorry, I multiplied the 100mA by 2 twice. 500mA should be fine. Don't go lower than 250mA.
Look in the LED resource. The is a constant current driver in there that will do the trick. It consists of 2 transistors and 2 resistors. One of the transistors will need to have a small heatsink.
If you tell me where you purchase components I may be able to point out some appropriate transistors.
In the case of the LEDs, digikey is considerably cheaper than mouser.
Just out of curiosity, how do the infrared security cameras stack up in terms of radiant power, etc.? I was wondering if they could be re-purposed for this situation.
The very cheap IR light with hundreds of LEDs has no detailed spec's. Some might produce a much higher output power than others or they all might produce only a tiny amount of output power. But it is Cheeeep!
Look in the LED resource. The is a constant current driver in there that will do the trick. It consists of 2 transistors and 2 resistors. One of the transistors will need to have a small heatsink.
Section 3. The table of contents terms you that constant current drivers are there
I linked to it in the message you quoted.
See the word "section".
It is a resource on this site.
Look in the LED resource. The is a constant current driver in there that will do the trick. It consists of 2 transistors and 2 resistors. One of the transistors will need to have a small heatsink.