Not enough actual research has been put into either to truly understand causes and effects of Lucid Dreaming and Astral Projection. It is, however, typically considered that an Out of Body experience is essentially a very vivid, very realistic Lucid dream.
The first difference is that once you realise you are in one, and the scope of what you are experiences; a Lucid dream is not frightening. You can control every aspect of the Lucid dream, and they have been shown to be a good antidote to constant nightmares.
How scary would a frightening monster or earthly cataclysm be if you could simply change it, instantly, at will?
An astral projection experience on the other hand, can be frightening, but for many different reasons. Lots of us have built up a belief system that we slot Astral Projection into. Of course, believing you are slipping into the ‘spirit world’ will likely be an uncomfortable thought.
You might discredit an external entity in a dream, but in an out of body experience, it might take on a whole new form of thought. A spontaneous astral projection experience can be terrifying. How would you feel, floating above your body, in your room? You wouldn’t be wrong to assume you might be dead.
Going on the topic of fear, astral projection is also tightly linked to sleep paralysis. In fact, in order to bring on the sensation of leaving your body, you have to essentially force sleep paralysis on yourself. As an experience, this can be a tough one to face.
You can experience all manner of sights, sounds and sensations when you are laying in bed, waiting for your body to fall asleep. Visual hallucinations are very common, personally when I attempt astral projection, I almost always see colours swirling behind my eyelids, usually streams of yellow which crash like waves and form shapes.
Lucid dreaming has no such relation to sleep paralysis, though usually as lucid dreams are often induced via and existing dream, rather than from waking consciousness.
Flying is a commonality within both astral projection and lucid dreaming. Within an astral projection experience, the projector will normally fly or float as their main means of travel, as there is nothing sticking them to any surface, and gravity won’t affect them. They can phase through objects as if they were a ghost.
Rarely would the projector walk, or run in order to get around. Lucid dreaming can involve flying, but often not. While anything is possible in a lucid dream, the dreamer is often grounded to reality in one way or another. Objects will still feel they have mass, and the dreamer is more a character in the dream world than a ghost in the real world.
Awareness of the body is what really separates an out of body experience from a lucid dream. In a lucid dream, you realise you are dreaming, in a dream world that is quite unlike the real world.
You are a character in a reality you have created. If you are having an out of body experience, you realise you are in the real world, and that you have an actual body, somewhere which you can likely visit, and see yourself sleeping.
Finally, many more people experience a lucid dream, than an out of body experience. While an out of body experience is not uncommon, lucid dreams happen far more often.
If you haven’t had a lucid dream before, it is likely that you will experience one in future. However, astral projection, or an out of body experience, is a bit rarer. It is unlikely that it will just happen without any input in your part.
While these differences are quite clear, I still think there is a lot of crossover. Both experiences at best are very similar to each other, and if you were experiencing either for the first time, it might be difficult to tell them apart. Regardless, both experiences can be life changing and above all, enjoyable.