OK, well, that doesn’t really help me very much. I’ll answer my own question, then. If what you mean is lightning occurring with no thunder, then the answer is: yes, it is harmful, but probably not to you at that moment. If you ever see flashes of light far on the horizon (what people refer to as ‘heat lightning’), you often do not hear thunder associated with these flashes. Seems counter intuitive, since both are one in the same, right? Well, the reason there is no sound is because the storm is simply too far away to hear the thunder. Next time you’re in the middle of a terrible storm, count the seconds in between the flash and the bang (called ‘Flash to Bang Count’). Then divide by 5. So let’s say you counted 10 seconds. Divide be 5, that gives you 2. This is (very roughly!) how far away the storm is from you in miles. What you should notice is that the farther away the storm is, the quieter the thunder is. So it goes to imagine that there is some distance at which being able to discern the sound of thunder would be impossible (maybe about 10 miles or so? Not sure.)
Bottom line: All lightning is, or has the potential to be, harmful. You just have to be careful.. My rule of thumb is if I can see it, it is too close.