Mike's Railroad Crossing Forum

The visual "snap" of instant ON and instant OFF draw one's attention to LED lamps better than incandescent lamps.

Yet, some manufacturers add extra circuitry to slow the rise and fall of luminosity to resemble incandecent filament characteristics.

Why do they do that?

I thought the only LEDs that could do that are one specifically designed to do that like the Harmon LEDs

I never really thought those Harmon "fading" ones fade all that much (if at all). Certainly not as much as those Safetran fading ones...

I always wondered that myself. I've seen that fading LED technology on pedestrian crosswalks, too.

Crossbuck_Chuck wrote:I always wondered that myself. I've seen that fading LED technology on pedestrian crosswalks, too.

Perhaps that is done there to soften the on/off and lessen annoyance.

When riding in the locomotive cab of Amtrak, I noticed that traffic signals at adjacent intersections went into a four-way RED flashing mode.
Because we are used to the sloping up of intensity of incandescent bulbs, when those RED LED lamps illuminated instantly, they actually appeared to emit a brighter quick burst of light at the very beginning of their flash and then lower intensity to the regular lumen output.
Others also noticed.
It is just an optical illusion perceived in the brain.

I have read someplace that there are some people that are sensitive to LED lights and that those lights really bother them... to the point that it distracts their attention while driving significantly. I think where I read it was in regards to some passenger vehicles now having LED taillights... like the Cadillac DTS for example.

If you have ever been behind one of those that has their turn signal on, you can see the effect that Robert is talking about. When the light first illuminates, it looks like it is brighter for a second when it first comes on. Effect is even worse at night.