LE HDR - or Long Exposure High Dynamic Range - is a mode available on our mobile apps. It works like HDR photography, except there is a limitation around the minimum shutter speeds available.
The way Triggertrap Mobile interacts with your camera, is by using the remote control port. This means that the only control we have over the camera, is the same as you have when you press the shutter button yourself. Obviously, you cannot adjust the shutter speed or aperture from your shutter button, and so we cannot access this directly.
Instead, our long-exposure modes use the camera's Bulb mode to control the shutter speed. In effect, we are holding the shutter button down for a certain duration of time, and that's the length of the shutter opening.
Cameras react slightly differently to Bulb mode, and if you're getting unexpected results, please check out this knowledgebase article!