here are the reasons, it was writen for headlights but most of them still apply:
Quote:
1) The headlamp reflector can handle high temperatures (this usually means it has to be made of metal).
2) The headlamp lens can handle high temperatures (this usually means it has to be made of glass).
3) The bulb socket can handle high temperatures (this usually means a quality aftermarket one intended for the purpose).
4) The wiring can handle high currents (this usually means you built an upgraded harness as discussed in this thread).
5) The beam pattern is designed to throw very little upward light, to prevent glare to oncoming traffic, and to provide low-glare seeing (this usually means an ECE lamp meant for the side of the road you drive on).
6) The bulb's base is designed to safely carry high current (this rules out a lot of bulbs, especially 9004 and 9007s; H4 bulbs however have nice large terminals and metal/thermoplastic bases).
7) The bulb is well-made with attention paid to all specifications (the best way to ensure this is to buy from a reputable manufacturer, and avoid stuff made cheaply in Eastern Asia).
8) The lamp is aimed correctly and with care.
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