Replacing incandescent bulbs with LED bulbs in mandatory external lights is certain to make the vehicle technically unroadworthy, and in most cases will leave gaps in directional coverage of lights and often result in lights that are outside the legal colour range.
This may explain why finding the bulbs can be a bit difficult. (And any you find should have a warning not to use them on road)
The fundamental problem is that the reflector/lens of the fitting is designed for a filament that emits light in all directions and over a broad spectrum. LEDs have one (or several) point sources, usually each fitted with a lens to give a directional beam from each point, and emitting monochromatic or at best multi-line spectrum.
However, the problem is not, in practice as bad as the fitting of HID bulbs to headlights designed for filaments, simply because the amount of light is less.
But you need to be aware that while very unlikely to be picked up for them, an investigation following an accident could see you without insurance and possibly charged with driving an unroadworthy vehicle. (but even this is unlikely)
Note that these comments do not apply to lights which are designed as a whole unit to use LEDs, and are marked as ADR approved. But this is not what the question referred to.
John
John
JDNSW
1986 110 County 3.9 diesel
1970 2a 109 2.25 petrol
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