HF fluorescent lights

[Gordon TarlingParticipant @gordontarling37126]

Robin – TLC will deliver.

[Ian HewsonParticipant @ianhewson99641]

Not flourescent they won't

[Gordon TarlingParticipant @gordontarling37126]

Not quite right – the website says they are not suitable for standard delivery and give the option to ask for a delivery quotation, though that may prove to be uneconomical for a few tubes.

[MuzzerParticipant @muzzer]

The lifetime of an incandescent bulb is inversely proportional to the fifth power of the temperature (IIRC – it's been a few years now). The wearout mechanism is a bit unusual, since the filament gradually evaporates during operation. Most other components (passives and semiconductors – including LEDs) follow the Arrhenius Equation for both lifetime and reliability (which are quite different effects – see below). Generally, for an incandescent lamp, the temperature is fairly constant and barely affected by the installation. However, the voltage plays a significant role in temperature and hence lifetime, so even a small increase in voltage can result in a marked reduction in lifetime.

There's no reason why you can't achieve a good lifetime with LEDs is designed correctly. Passenger car LED lights are generally designed for 15 year / 300,000 km life and are tested accordingly. Thermal management is one key element to get right and you will see that the LEDs themselves are invariably mounted on IMS substrate, which is basically a PCB made on an aluminium sheet instead of FR4 substrate. Of course, if you don't have adequate cooling of that assembly, the components will run very hot.

I would expect that most of the problems with reliability and lifetime are down to poor circuit and thermal design combined with poor quality control in manufacturing. That's probably a good reason to buy well known brands rather than cheaping out on Pound Shop specials.

The difference between reliability and lifetime isn't hard to comprehend. A surface to air missile may only have a lifetime of several minutes (due to the limited fuel load) but it must have a very high reliability (ie an MTBF measured in the hundreds of thousands of hours), as many lives may depend on it. Conversely, a cheap biro may be very unreliable (air lock, ball falling out, ink leaking away) before the natural lifetime is up (ie ink has been used up). In the latter case, the reliability isn't so critical, as you can just throw it away and grab another one.

Murray

[duncan webster 1Participant @duncanwebster1]

Following the advice given here I've fitted an LED tube, which I got from Toolstation. Not as cheap as some, but can be picked up so no postage. 4000K which I think makes it cool white. Let's just say I won't be buying any more normal fluorescents. I hadn't realsied how bad one of the tubes in my shop had got until I fitted this one. Now a question, one of my fittings must be over 40 years old, and doesn't employ a starter. Is it scrap, or can I just fit an LED?

[clogsParticipant @clogs]

Hi all, on topic ……..

just a couple of days ago an old 5" flu started to flicker on and off every few sec's…….bought a new Osram tube and fitted it……instantly the end's glowed yellowy /orange, changed the starter and refitted the tube, same thing……

the tube will light up properly if I untwist the starter…..looking at the new tube with the power off, this new tube now looks burnt on the ends, thats inside the tube/glass looking like it's been working for years…….

not interested in a fix but would just like to know whats gone wrong……have 12 x 5" flu fitting in the w/shop and some extra double tube types as well and they're are all working fine……..did fit a 4" LED replacement tube a month ago with great results but cannot get 5" replacements here yet…….hopefully for the new w/shop they will b available at a good price at least comparable with normal 5" flu's……..

any ideas'…….thanks clogs

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