I don't have complete ones (cheap buy on eBay). However I have tested the component and the forward voltage seems to be around 1.09 V. Using a 9V battery and a variable resistor I have measured the lowest possible resistance necessary (around 250 ohms) to have some light (estimation with a webcam). So I don't think safety is a concern anymore. I have lowered the resistance down to 120 ohms with 3 LEDS in series. The circuit is not heating but the current seems to drop quite fast. I don't know if this could be a multimeter issue but the current falled from 75 mA to less than 30 mA in a few minutes. At that point I switched the circuit off to spare the battery. So I am still wondering if I could have a better powering circuit because I am afraid to empty the battery quite fast (even if the one I have been using for the test wasn't full and was giving 7.6 V rather than 9 V at start).