Hello and welcome to the forum. Headlight bulbs do lose their brightness over time, and it may well be time for you to replace the bulbs. There are two low and two high beams. But rather tham me going thru the whole thing again, just try using the search box at the right side of the opening screen and type in "headlight" Then you will be presented with plenty to read about your headlights. Best of luck
The GL1500 has two headlight bulbs. Each bulb has a low and high beam. The stock bulbs are 45 watt for low and high beams. Lots of folks have replaced the stock bulbs with H4 or 9003 bulbs available from many auto parts stores. They are 60 watt for high beam and 55 watt for low beam. They provide a nice enhancement for headlight illumination on the GL1500. Have them on my '99 Gold Wing SE.