Headlight and bulb

The headlight is the main lamp at the front, with a reflector, lens and a bulb or LED module. Many bikes also have a small position (parking) light in the same unit. The K-Light 125 uses an H4 halogen bulb with two filaments, one for low beam and one for high beam.

What it does

The bulb lights the road and makes you visible. The reflector and lens shape the beam so low beam does not blind others. Halogen filaments wear and break from vibration, heat and high charging voltage. Oil from your fingers on the glass makes a hot spot that shortens life. Water inside the unit fogs and rusts the reflector.

Signs it is worn or failing

• Headlight does not work.
• Headlight is dim or flickers.
• High beam or flash does not work.
• Bulbs keep blowing: check charging voltage.
• Blackened bulb glass or a cracked, fogged lens.

When to replace it

Replace the bulb when a filament is broken or the glass is dark. Replace the lens or unit if cracked, if water stays inside, or the reflector has lost its shine.

What to match when buying

• Match bulb type (for example H4), voltage (12 V) and wattage from your manual or the old bulb.
• Look for an approval mark ("E" in a circle and a number) on bulbs and lamps. Philips notes that some marked bulbs still have a poor beam because cheap makers do not keep production to the approved design; buy from brands that also supply the bike makers.
• Very high wattage bulbs overload the wiring and switch. LED "retrofit" bulbs in a halogen lamp can give a poor, glaring beam and may not be legal; check local rules.

Fitting notes

• Rider job: Replace a bulb. Let the bulb cool and do not touch the glass; clean it with alcohol if you do.
• Seat the bulb tabs in their notches, refit the rubber cover, then aim the headlight.
• If power is missing: Test a lighting circuit.

Reference (K-Light 125)