Trying to make this effect in eevee:
I'm looking to make a glowing trail of light, in eevee, which starts of bright but tapers away into darkness. It needs to be able to be locked to follow the motion of another object.
I have a stream of particles following the eye: newtonian physics, 0 gravity, 0 velocity. They fade from bright to nothing using the process @atomicbezierslinger gave.
While the particles do follow the path as hoped for, they don't 'connect up' yet. The easy fix (in the above image) is just to have a high 'Number' (2500 for each eye in this case).
I had an issue where the particle appeared in 'clumps' every frame. This was because it was parented to an animated object which moved only on every frame. Baking the motion and removing the emitter's parent fixed the problem.
I'll try the process @RichSedman linked later. It may well be a better solution.
Thank you for the advice.