I was thinking it would be interesting if there was a sight that used fiber optics such as mepro21 or trijicon, but using an led to light it up? no? maybe?

People have taped small LED lights to the FO feed of a Trijicon optic to do exactly that.

it seems like it makes sense

It gets too bright. The fiber optic by itself works just great. Even just that, gets too bright sometimes.

The Leupold Firedot reticles use a fiber optic tube to transmit the small .3 mil dot to the reticle from the LED.  This enables the dot to stay perfectly round, maintain true color, and not bloom at very bright daylight intensity settings, if cranked up that high.

This also allows the battery and brightness control to be moved away from the eyepiece to the left side of the turrets.

However, the fiber optic tube is encased except at each end, so there is no way for ambient light to illuminate the dot.

I like your idea.  It would seem a small step for Leupold to accomplish what you propose, as most of the system is already in place.

There is already a device like that for the Mepro 21 - the Wash Out Remover. Been around about a year now. Some guy at the Bullpup Forum made them.

I have three Mepros. My first 2 honestly never wash out. You can always see it a little. My last one isn't so lucky. The reticle isn't as bright in some instances, unfortunately. I got a wash out remover attached in the rare instance it would be an issue in live use.

http://www.bullpuparmory.com/product_p/hg-wor-m21.htm

I never got one until this 3rd Mepro, because I didn't need it.

You mean like the Trijicon Tripower?