I'll join the crowd on this one. My deceased Rott was so bad he would chase my watch crystal reflection from the sunlight. If it was reflecting on the ground or a wall he kicked into high gear, much to the amusement of the neighborhood kids. The only benefit that I can claim is once in a while I used this to trim his nails on rough concrete. Back and forth and around and around he would run. I use a more conventional nail trimming method with my new pup.

no no no no. Trust me, you do not want to do that with any high prey drive dog.
Tucker came to me with this exact problem. And we still have not been able to sort it out. It is 10 times better than when i first got him, but its something he will still do if given the chance
It is EXACTLY like OCD in a human.
He will chase any form of light or shadow to the point of exhaustion if left.
He is completely obsessed with light and if he sees anything, and i mean ANYTHING light wise he's on it. Light off the watch face on the wall, he's there, if im fiddling with a cd and it happens to catch the light and shine on the wall he's there, cars passing by outside and their headlights shine in and hit the wall, again, he's on it. Same with shadows, birds fly by he chases their shadow, it was snowing the other night and he was actually chasing the shadows of the flakes on the ground. He wasn't looking at the flakes, he was only looking at the ground and jumping on the shadows the flakes caused.
I can control it with him now and he will down and stay there but he is still completely focused on any light source and his body is so tense and ready to jump its crazy. He will re-focus on me if i call him, but he still shifts his eyes every few seconds to try and see where the light has gone and as soon as he's released he will search frantically for the light.
Its a bit sad actually and something i don't think he will every get over.
He is a rescue dog that was horribly neglected and unfortunately his only form of amusement while being tied up by a chain was to chase shadows and light on the ground. He was 3 when I got him so it is completely ingrained into him now as a source of entertainment that its something i will probably just have to live with. I am used to it but have to be very very diligent when it comes to moving lights around him.
And before anyone asks...he is exercised so it has absolutely nothing to do with him not having enough to do. He will be in the house after a long hard hike flat out on his side having a rest the second he sees light, he's up.
I do remove him from the situations and don't allow him to do it. But its still a habit he can't seem to shake.

I think it really depends on the dog, but as has been stated before, it may not be worth the risk to find out. I have one Chi who is slightly light obsessed, not totally. Flashlight, laser light, reflections off anything, even her own tags. But it isn't constant, she doesn't spend all her time looking like some dogs. With her if she gets started, she doesn't want to stop. It is kinda cute in a chi, I can only imagine how bad it would be in a large, high prey drive dog. I don't want my 100 lb boy jumping on me to get to a light, like my chi has...

This is something I've never really heard of, neroticism(?) from lights/lasers. My dog shows no interest, but this thread is definitely an eye-opener.

I have had a couple of dogs brought in that there owners said they chase shadows obsessively. They told me it all started with a laser light. I would have to say this is not a good idea.

Gunman

I also agree that the use of laser lights is not a good idea. It does depend on the dog, but if you have a dog that is not interested, they won't play - and if you have a dog that is interested it could develop into a serious problem. Personally I do not like the risk.

The obsessive behavior, I think, comes from the fact that the light can never really be caught - the dog comes as close as it possibly can, mouthing the wall or floor where the light is, but the light never goes away, and the light cannot be caught, shaken, and played with.

The laser is prey that only builds frustration in the dog - which will either cause the dog to ignore it and go for a toy that can be caught, or to become fixated on catching this elusive, but ever present, prey.

My 14month old rott chases shadows. When he was a pup it was amusing, something none of my past dogs had done. i was then warned by a rott breeder friend of the obs comp behaviour that could develop. I ignored her warnings, not encouraging the behaviour nor challanging it. Now in the house any movment that results in a shadow can set Bos off, he will be wound up for up to a hour and will not settle. I am therefore challanging this behaviour at any opportunity. i have been told though that now he has this obs comp behaviour he may well redirect it. If only i had listened to the wise.....

Ditto with all of the posts. Do not play with a laser light with a dog. My 2 yr old GSD is obsessed with lights, will sit and stare and chase at shadows, watch reflections, TV reflecting off fishtank, car going by and breaking sunlight, glass door reflection...and on and on. Flashlights are a huge pain when taking them out at night, or trying to do something in a small space with a flashlight...her nose is right there. Setting up the Christmas tree was a treat.

All started I think with a laser level when I was doing work in the house. Thought it was cute at first. Will never do that again.

Don't know if it started with a lazer toy, but my mother's rescue dog is light/shadow obsessed. After a year of regular obedience work, she can now put the dog in a down-stay while Dad washes the dishes. This used to be a very trying time of day as the dog would see the light on the ceiling from the pans... The dog is still obsessed, you will often find it with it's nose stuck in a corner, pawing at shadows, but it now knows that barking at lights in the house is not acceptable behavior.

Is there any recommendation on how to handle a dog that is light/shadow obsessed? My fiance teased my GSD with a laser light a few times when he was 4 or 5 months old. Now, at 10 months old, he's been shadow/reflection obsessed for the last 4 or 5 weeks! It is so sad. He'll just stare at the floor, drooling, whining, scream-barking, trying to anticipate the shadows next move. He won't calm down. He paces, cries, barks, tries to bite the wall, jumps at the ceiling, all kinds of rediculous things.

He is excercised daily, though not 'hard' becuase of the weather lately. We go on 2-3+ mile walks at least 3 times a week. We do obedience training nightly. I just don't know how to get him to stop this nasty habit. It's really scaring me, thinking my dog is broken or something now.

He will refocus on me if I throw a ball or a toy he likes, but it doesn't last. If we're training, he doesn't care about shadows or lights. If we're playing constantly, he's ok. If I'm not constantly entertaining him, he reverts back to his crazy shadow/reflection fix and I have to literally grab him by the neck and make him look at me for his attention to get on me again. It's like he's in a trance when shadows/reflections are around. If anybody has any suggestions on how to fix this, please let me know. I'm desperate!