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Scenario

I'm changing my left headlight bulb and it says it is a H7U one. What does the U marks?

Possible solutions

I searched a bit and found two possible solutions:

  • Marks the shape of the bulb.
  • The bulb is not ultra violet sensitive, therefore it is suitable for use in Parabollic Plastic Reflectors.

I saw the first one mentioned on multiple sites, the second one was told by this guy:

H7U means the bulb is NOT ultra violet sensitive, therefore it is suitable for use in Parabollic Plastic Reflectors as fitted to the later Astra's Ordinary H7 halogen bulbs can cause yellowing to some plastic reflectors as experienced in Ford Mondeos

Question

What is the truth? Does it really indicates shape? What does the shape influence then? Why would there be different type of shapes?

Community
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totymedli
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2 Answers2

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This is an ad by Sylvania:

100% NEW Genuine Osram / Sylvania H7 Halogen Headlight Bulb.
Osram / Sylvania #: 64210 / H7 12V / 55W / PX26d / UV Filter
Acura Honda Hyundai Infiniti Porsche Toyota Mini Land Rover Mercedes Benz BMW Volvo Volkswagen Audi VW

Quartz-halogen lamps put out a lot of UV as a side effect of how they work and the bands of light they emit.

This ad implies that H7U bulbs have no UV filter, which is bad for the eyes and some plastics.

The LED versions are H7 only, but would put out a small amount of UV light by design.

After scanning many internet pages, the H7 (including LED versions) seem to dominate the ads.
It would seem the H7U is being phased out due to high UV emissions.
I found this snippet of text in Wikipedia on Halogen lamps:

Main article: Automotive lamp types: Tungsten-halogen lamps have been commonly used as the light sources in automobile headlamps, but are increasing being replaced by Xenon and LED lights.

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I have a 2007 Lotus Elise. "Pre" 07, Lotus used H7. 07 and later, Lotus went to H7U. The U is ultraviolet "filtered." Previous poster (commenter) is wrong. The cheaper (and older) H7, put out tremendous ultraviolet light, damaging the headlight covers, degrading their clarity over time. Just do a Google search "2007 Lotus Elise headlight replacement" and lots of posts from the Lotus community. Those exotic car owners know their stuff.

John
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