For emergency use I have an LED strobe light bar. It emits 2,000 lumens of red LED light(clear lens) of unequal random flashes. On a long, long, vale, some THIRTEEN MILES long on Mex 37, a friend said he was near blinded. I was parked on the far side, off center, nose facing uphill car about 30 degrees pointed to starboard. This is in excess of TWENTY KILOMETERS distance. The lamp has Hi, Medium and Low intensity settings. I loaned it to the Seguro Popular Ambulancia because they had complained bitterly to me drivers did not yield to them when they went code 3. They later remarked "We no longer have that problem".