Vehicle HeadlightPractical lighting guidesThere is no single service life for every halogen, HID or LED headlamp. Use the exact product’s published life rating and the vehicle’s service guidance. Operating hours, usage pattern and faults matter; an advertised hour figure is neither a warranty nor a scheduled replacement date for your car.
What B3 and Tc actually mean
OSRAM explains B3 as the time by which 3% of tested lamps have failed, and Tc as the time by which 63.2% have failed. They describe a tested population, not the remaining life of a bulb already installed in your car. Compare ratings with the same definition and test conditions. [1]
A product listing that only says “long life” gives less decision support than a specific rating with a clear definition. Keep the exact part number when comparing a high-output version with a long-life version. Do not transfer a rating from one bulb family or technology to another.
Turn a rating into a usage scenario
For an illustrative calculation, 500 operating hours divided by 1 hour of use per day is 500 days. At 2 hours per day it is 250 days. The 500-hour number here is an invented arithmetic example, not a rating for your bulb. Automatic lighting and daytime use can make actual operating time different from night-driving time.
Even with a real product rating, dividing by daily use gives a scenario rather than a failure forecast. A laboratory population statistic cannot tell you which day an individual lamp will stop working. There is no countdown in our checklist.
Why the same part can last differently
- OSRAM lists vibration, temperature, supply and socket corrosion among halogen failure factors. [1]
- HELLA notes that overvoltage shortens filament life and low voltage reduces output. [2]
- Handling or installation concerns should be checked against the bulb and vehicle instructions.
- For an LED headlamp, a driver or other component can fail even when the LED emitters are not the immediate problem.
A lamp that fails repeatedly deserves diagnosis. Keeping a box of replacement bulbs in the car may hide a supply, mounting, moisture or connection problem. Record dates and exact parts rather than assuming that every failure means poor bulb quality.
Build a useful maintenance record
| Record | Why it helps |
|---|---|
| Date and approximate mileage | Shows repeat failures without implying a fixed interval. |
| Lighting function and side | Separates low beam, high beam and daytime running use. |
| Exact part and source | Allows the application and product to be checked. |
| Visible symptoms before failure | Color change, flicker, moisture and heat guide the next inspection. |
If the manual or manufacturer recommends paired replacement, follow that instruction. Matching service history can help with consistency, but paired replacement is not a substitute for finding a recurring fault.
When to act before the bulb goes out
Arrange a check for new dimness, intermittent operation or warnings. Stop using a system showing smoke, melting or a burning smell. If road visibility is inadequate, do not continue driving to test whether the other lamp will last. Use the symptom check to create a concise workshop note.
Keep the handling instruction with the part
The halogen-glass handling guide separates contamination from other failure causes. Retain the full marking and product reference with your service dates.
Sources and scope
Numbered references support the technical points above. Consulted November 5, 2026. Your vehicle’s documentation takes priority for its specification and service procedure.
- OSRAM: Vehicle lighting FAQs — B3, Tc and failure mechanismsService-life definitions and halogen failure factors, not a vehicle-specific interval.
- HELLA: Maximising bulb lifeSupply voltage affects filament output and life. No universal charging-system test thresholds inferred.
Examples and decision tables are editorial illustrations, not diagnoses, product tests or universal instructions. How we work.