USB powered IR emitter for night vision webcam
Your best bet is to buy these IR LEDs with 1.1 watts/sr @100mA @1.5V and use a string if 3 LEDS using 0.5V drop from 5V across a 5 Ohm 1/8W resistor. (verify current with a meter from V drop)
If you can supply 200mA use two strings of 3 LEDs each with a 5 Ohm R.
we call this an array of 3S2P.
If not, then use slightly higher R. So buy a bunch of different R's like 5-10 Ohms or use 10's in combinations to make 7.5 Ohms and a dozen or more LEDs (cheap) . 
If you use the HDD connector 5V, you can add a switch to enable as many IR LED strings as you want and put them in a bundle to make a super strong 6 deg IR LED spotlight.


LED angles are always full angle while IR LEDs historically were half angle, but recently some disti's show full angle to avoid newbie confusion. So this LED is technically a 3 deg half angle and your bundle may spread this depending on alignment. 

doubling the angle will reduce the peak intensity in half approx. (except for lens loss with narrower angles)
then intensity drops inverse squared with distance.
warning , do not stare at the bundle up close