I'm trying to find a 940nm SMD infrared led with minimal red glow at night.
The TSAL6400 gets close to it, but it's still not completely invisible and not SMD.
I've noticed IR leds have different wavelength curves in the lower range. TSAL6400 through hole with blue lens vs VSMY2943G SMD with clear lens.
I've tried covering them up with an infrared transmitting acrylic sheet but it's completely transparent to the red glow.
My guess it that the radiance on the lower end of the spectrum goes to close to the RED range. Although it's still infrared, the eye is still slightly sensitive to it.
How do I eliminate the red glow visible to the human eye from an IR led?
VSMY2943G
Best Answer
The human eye response stops at around 700nm to 750nm, you might be picking up a small amount of red because there are still a few photons in the red range produced and the eye is really sensitive to them in the dark. (its been theorized that the eye can be used as an individual photon detector.)
Source: http://hyperphysics.phy-astr.gsu.edu/hbase/vision/colcon.html
My suggestion would be to get a high pass optical filter at 850nm or 900nm and see if that solves your problem. And you can't stop all of the photons from getting through, only attenuate them. Maybe an IR laser, that transmitted at 850nm or 900nm might work also as the bandwidth is much smaller than an LED and will have less (almost no) 'leakage' into the 700-750nm range.