Comparison between H4 and H7: Differences between headlamp bulbs
Discover the advantages and disadvantages of H4 and H7 lamps.If you're wondering which headlight bulb is better – H4 or H7 – then look no further. We explain the differences.
How does an H4 lamp work?
H4 lamps used to be standard equipment in vehicles. They are referred to as Bilux lamps. What does that mean? They have two filaments: one for the low beam and one for the high beam.
The individual filaments are activated when the respective light function (low beam or high beam) is switched on. The reflectors in the headlamp are precisely matched to the position of the filaments so that the light cone is cast in front of the vehicle accordingly.
Features of an H4 lamp:
- Two filaments in the glass bulb
- A lamp base plate in the headlamp
The next level: the H7 lamp
The H7 lamp is a further development of the H4 lamp. It has only one filament. You need two H7 lamps per headlamp: one for the low beam and one for the high beam.
The advantage of this arrangement is that when the high beam is switched on, the low beam does not switch off, and instead remains functional. This means that the area directly in front of the vehicle remains well illuminated.
Features of an H7 system:
- One filament per lamp
- Two lamp bases plate per lamp
H4 or H7: Which is better?
The luminous efficiency of H7 systems is higher than H4 systems because of the combined effect of the two lamps. However, with H7 systems you need four bulbs (2 bulbs per headlamp) instead of two, and both sides should always be replaced at the same time because then they will have a similar lifetime. This leads to higher costs over time.
Replacing H4 with H7: Is that possible?
It is not possible simply to replace H4 lamps with H7 lamps, as:
- The base plate types are different: an H4 lamp does not fit an H7 lamp socket and vice-versa.
- The reflectors in the headlamp are matched to the position of the filaments. If this was changed, the light cone would be projected incorrectly onto the road.
Use of adapters
Important: Adapters are not recommended. These kinds of ad-hoc solutions can invalidate your vehicle's operating licence and lead to problems at the next general inspection.
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