8

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?

  • great detailed question. +1 – DucatiKiller Apr 22 '16 at 23:15
  • I see no mention of shape in your information you posted? It has to do with UV light they emit, nothing more. – Moab Apr 26 '16 at 23:38
4

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.

  • 1
    Given that both versions put out a usable amount of visible light (thought some complain the LED versions seem dimmer), I would avoid any UV emitting products period. Some LED back-lit monitors and TV's have the same issue-they can make your eyes hurt from the brightness. The manufacturers recommend turning down the brightness to 70% or so. – user16540 Apr 23 '16 at 0:23
  • The OP deleted his comment? – user16540 Apr 23 '16 at 0:26
  • Yes, I re-read your answer and wanted to ask a different question: If UV is bad why H7Us exist? Are they older/discontinued products (and we should go with plain H7 ones) or there is some kind of benefit in them? – totymedli Apr 23 '16 at 0:30
  • Like old airplanes that were prone to crashing, the H7U series was the first to market, and we all know that marketing and sales want to recover their investment fast (ROI). The Ford Pinto was designed with bladders in the gas tank and a rear shock bumper. but the mfg plant left them out to save $2,000. We are the guinea pigs until proven a hazard. – user16540 Apr 23 '16 at 0:38
2

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.

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