Bulkhead wall lights and jelly jars (vapor tight fixtures) are very similar in looks, but they are different. Jelly jars usually come with a round light and a piece that attaches to the wall, whereas a bulkhead wall light is always flush mounted to the wall. A jelly jar can be mounted to the wall or the ceiling.
Each fixture also replaces different types of lighting fixtures and are better in different locations such as bulkhead wall lights being better for outdoor lighting and jelly jars better and more appropriate for indoor lighting. They also have different beam angles.