The sun also emits in the visible wavelengths. Your eyes do not feel pain from bright lights due to the heat or similar. It's a response to brightness, in the visible spectrum. Without the visible component, there's no pain. With unhappy optical circumstances it could cook the retina because the pupil is dilated and there's no instinctive response to look away. Not sure how plausible those circumstances are. But I sure wouldn't put a 10 watt IR LED source right up to my eyeball.