If that distracted player doesn’t bring it up to a TD … It doesn’t mean anything to me as that TD.
I did receive an official complaint from someone’s head lamp usage at Nationals last year, and they appropriately received a yellow card. There were no more complaints filed of that player the rest of the tournament.
It can, if the light’s direction is more in your face, or if it’s brighter than the individual machine lights. In my case, it was enough to notice and a brief nuisance, but not enough to report, so I let it slide. But it could easily have been more of an issue, so I mentioned it when this thread arose.
Side thought: maybe I should wear IR filters on my glasses when the LEDs are too bright? 
There are multiple things to consider here. If it’s on a different machine, then no. If it’s reflecting off my machine’s backglass, then yes. Headlamps are also not static lights, they move around as the player moves around and that movement alone can cause a distraction. Note that “distraction” here doesn’t mean that the light is too bright or something like that, it’s the fact that it exists and causes the brain to stop to process it for a split-second, and that could mean the player losing control and draining.
At our league, we typically have a few banks of overhead lights always on, but sometimes people bump the switch and turn them off. This almost always results in every active player calling out “hey, don’t mess with the lights!” Any non-normal change in lighting while playing is usually noticed pretty quickly.
To put this another way, would you be ok if I stood over your shoulder with a Maglite, and pointed it at the backglass/playfield and waved it around while you were playing? I would suspect not.
Josh is right here though, if it’s not reported then a TD can’t really address it. Best plan for anything really is to bring it up if you think it’s a problem, because not everyone has the same thresholds for what is and isn’t distracting.
Yellow card on the first notice? Or did you ask first and when they kept using it you yellow carded them?
He was aware before the tournament started that he would receive a yellow card if anyone filed a complaint to me about being distracted by the lamp.
After the yellow card he continued to use it the rest of the tournament, but made a better effort to keep his head down on the playfield. He also made sure he turned off the lamp before moving away from the game. No further issues came up the rest of the tournament.
I believe the distraction came up when he accidentally forgot to turn his lamp off after his turn ended, which caused the light to bounce off the game next to him as he turned around to walk away from his machine.
If, during the course of the rest of the tournament, another player had complained, he would have gotten a red card and been ejected? Or would there be one more yellow card?
Tilt . . . all data lost.
That’s a pretty gutsy move to keep playing with it knowing the potential consequences.
I had never seen or heard of this before until the 24 hour final battle. Never had any direct complaints. People asked me if it was legal. I said there is no rule against it currently as I see it as a TD but if I get complaints we will address it. I did have several people say if they are playing next to me I know that’s going to be distracting and I’ll be sure to complain. Guess what? No one complained. Either it wasn’t as distracting as they thought (likely) and/or the person was very diligent about never looking to the left or right before turning the light on/off.
As a TD I know everyone is looking for a reason to complain and blame their bad performance on 
I’ve played in multiple tournaments with that player, and he’s actually REALLY good about keeping his light on his own machine. It must have been a really weird moment that caused him to look away from his game with the light on.
This will probably never come up, but if the player is legally blind then a headlamp probably qualifies as a reasonable accommodation under the ADA. In such a case you couldn’t outright disallow it and you’d have to be careful about issuing cards for disturbing other players.
I agree on not disallowing it, but penalty cards should be fine as long as rules are clear up front: “Any player-supplied lighting can only be directed at that player’s playfield, and in a manner that is not distracting to other players. All player-supplied lighting devices must be extinguished before they are aimed anywhere other than that players playfield. Failure to do so may result in a warning or DQ.”
This seems like a perfect opportunity for a modder. Something that gently, but firmly, clamps to the head with a pivoting extension that goes over the playfield. One LED (or whatever lamp) for the upper playfield and one for the lower. Maybe shields around side to prevent stray light. Battery operated. Rolls up and fits in a bag when you’re done. Quick removal between balls in multi player games.
Someone should start a thread on pinside. Lots of modders there. Something like: ‘Mod Needed’ would probably get some bites.
even easier… lamp with magnetic base and flex arm that mounts to the lockbar. That area is usually behind the line of sight of the player… and would wash out towards the backbox… not other players.
I’ve done that too, although it may not have been accidental. 
the thing I don’t get is that if the headlamp is meant to make it easier to track the ball, how does it work given you have to track the ball for the headlamp to illuminate it? chicken/egg right?
The beam must get pretty wide for something three or so feet away. I’m thinking of those battery brand headlamps you might impulse buy at the Lowe’s or something.
go back and watch the IFPA nationals for 2016. You can see the concentrated circle of light dart around the playfield, it doesn’t look like a wide beam at all.