Headlight Housing Buying Guide
Last updated: 24 April 2026
Headlights provide essential forward illumination for safe driving in low light and poor weather. Modern headlight units are complex assemblies incorporating dipped beam, main beam, daytime running lights, and indicators. Cracked lenses, moisture ingress, and faded reflectors all reduce light output. At CarParts247 we stock headlights from Hella, Valeo, and TYC.
Common headlight problems
Headlight performance degrades over time even if the bulb is fine. Clouded lenses and moisture are the most common issues, followed by wiring and connector failures.
- Clouded, yellowed, or hazed lens reducing light output
- Moisture or condensation inside the headlight unit
- Cracked lens from stone impact — allows water entry
- Dim or flickering light — corroded connector or failing ballast (xenon/HID)
- Failed MOT for headlight aim, pattern, or output
Headlight replacement and alignment
After replacing a headlight unit, beam aim must be checked and adjusted to avoid dazzling oncoming traffic. Many modern vehicles require coding or calibration for adaptive headlights.
- Check that the replacement unit matches your vehicle spec (halogen, xenon, LED)
- Adjust beam aim after fitting using the built-in adjuster screws
- Replace any cracked or missing lens seals to prevent moisture ingress
- Test all functions: dipped, main, DRL, indicator, and levelling motor
- Adaptive or matrix LED headlights may require dealer-level calibration
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Halogen, xenon, and LED headlight units — lens clarity, projector vs reflector, and E-mark compliance.
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Frequently Asked Questions
Can I upgrade halogen headlights to LED?
Retrofit LED bulbs in halogen reflector housings are not road-legal in the UK because the beam pattern does not meet regulations. A full LED headlight unit conversion with proper E-mark approval is the legal route.
Why is there condensation in my headlight?
All headlights ventilate through small breather holes. Light misting that clears when the headlights warm up is normal. Persistent pooling water indicates a cracked lens, failed seal, or blocked vent.
How do I fix cloudy headlight lenses?
Polycarbonate lenses can be restored with a headlight restoration kit (wet-sand and polish). Apply UV sealant after polishing to slow re-hazing. Severely degraded lenses should be replaced.
Do I need to adjust headlight aim myself?
After replacing a headlight unit, aim should be checked. Most garages and MOT stations can do this quickly. Incorrectly aimed headlights are an MOT failure and a safety hazard.
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