CDM (Ceramic Discharge Metal Halide) and CMH (Ceramic Metal Halide) lighting are both popular types of lighting used in hydroponics. They are similar in many ways, but there are some differences between them.

CDM lighting uses a ceramic arc tube to produce light, which contains a mixture of gases and metals. This produces a bright, white light that is similar in color to natural sunlight. CDM lighting is known for its high efficiency and long lifespan. It also produces less heat than other types of lighting, making it ideal for use in hydroponics.

CMH lighting is similar to CDM lighting, but it uses a different type of arc tube that is made from ceramic metal halide. This produces a light that is also bright and white, but with a slightly different spectral output than CDM lighting. CMH lighting is known for its high efficiency and long lifespan as well. It is also a popular choice for use in hydroponics.

Both CDM and CMH lighting are great options for hydroponic growers who want to provide their plants with high-quality light that is similar to natural sunlight. They are both efficient, long-lasting, and produce less heat than other types of lighting. The choice between the two will largely depend on personal preference and the specific needs of the plants being grown.