Electrical/Electronic Tech Quessie (Life Hrs)

[addo]

I'm looking at these dash bulbs from Farnell/Element 14:
http://uk.farnell.com/cml-innovative-te ... dp/1139315

They say life is 1000 hrs. That's not much.

However, here's the datasheet. Note its stated mean life: http://www.farnell.com/datasheets/20345.pdf

Which do I believe? It's not like Farnells sell junk.

Cheers, Adam.

[xmexclusive]

Hi Addo

Perhaps the 6k hrs the working life where you switch it on and leave to run in a test rig.
If you use it in service with regular on/off switching surges perhaps working life will typically be 6 times shorter.

John

[White Exec]

Hi Addo,

For normal tungsten lamps of low wattage (which these are), and decently constructed, the service life is not much affected by frequently switching on and off, as compared to a continuous burn.

What does affect service life drastically is the design/supply voltage. For automobile use, you should try to source a lamp* rated at 14v, not 12v, since this matches the supply voltage in normal driving use. Again, for normal tungsten lamps, reducing the voltage by just 10% will extend the lamp life to around 400%, while light output will still be around 85%. Upping the voltage by 10% can reduce lamp life by around half.

For dash/instrument lamps, it's always a good idea to use the dimmer control to reduce the illumination level, for the reasons above. When used thus, instrument lamps can outlast the life of the car, very often failing because of poor lampholder contact, for which Citroen has been somewhat famous.

Chris

* eg these: http://uk.rs-online.com/web/p/filament- ... s/6559637/. There are others on the RS site similar.

[addo]

I'd plain forgotten RS - ta for the link. Pricing is about neck and neck.

The Farnell's TDS is quantified at 13.2V and seems to cover the subject of failure in a more rigorous manner than simply stating a service life. Doesn't make it a better product, though!

Hmm...


(And before Peter N suggests it, 12AX7s may produce a lovely warm glow but they don't fit in the bulb holders.)

[Peter.N.]

Ah bother - you beat me to it