Having the door open is dangerous but can lead to better photos. The microwave oven shown here was modified to allow it to operate with the door open. Running a microwave oven with the door open can damage the magnetron, since the tuned cavity is no longer present and causes the magnetron to slowly overheat. Escaping microwave radiation can damage nearby electronic equipment, so keep things like household appliances and cameras well away.
Microwave radiation can also do a lot of damage to humans.
The amount of microwave energy being put into the fluorescent tube will not be as great with the door open. I ran the oven with the door open, so that the grill wouldn't interfere with the photo. Doing the experiment yourself Picture showing the tube taped to plastic film canisters. A glass of water could be added to reduce the chance of damage to the magnetron. Use an old fluorescent tube, since the oven will permanently damage it.