Is there any difference between these two?

In Premiere Pro the default setting for broadcast is 110 IRE, but someone told me that 100 is safer. Wouldn't the picture get too dark with the 100 IRE setting?
Can I assume that 110 is really safe for broadcasting?

that depends on whether you're talking luma or luma plus chroma. Luma and chroma together come out at 110%

Analog transmission imposes a limit of 120IRE for the broadcasted composite signal (the composite signal is the luma and chroma modulated together). Though in practice, you don't want to go above 115 IRE (since some old receivers will have problems with stuff >115 IRE) and the broadcaster may have a signal chain that sets the limit lower (e.g. they may store material on analog formats, which distort if the IRE level is too high). So check with your broadcaster as to what the maximum composite IRE level is.

HD generally isn't broadcasted the same way as SD NTSC and PAL so it doesn't have the composite IRE limits AFAIK.

Wouldn't the picture get too dark with the 100 IRE setting?
Not really. It limits how saturated bright colors can get; though your legalizer (whatever hardware or software makes the signal legal) may try to keep saturation the same by lowering brightness. So saturated colors may not be as bright as they should be. But it doesn't make sense to limit at 100 IRE.

Thanks guys