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HF fluorescent lights

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Robin Graham14/07/2017 22:39:04
361 forum posts
41 photos
Posted by Gordon Tarling on 13/07/2017 11:27:04:

Robin - I thought the same as you regarding lumen ratings until it was explained to me by a US pal. A standard fluorescent tube radiates light around its entire circumference and much of the light which goes above the horizontal is lost unless you are using some kind of reflector above the tubes. An LED tube only radiates light below the horizontal, so the perceived brightness is a bit higher. I had standard Tri-phosphor daylight (6000k) tubes rated at 5200lm in my shop and am replacing them with 24W Cool White tubes that are rated at 3230lm - the LED ones definitely make the shop brighter, though that could just be my perception.

Thanks Gordon, that makes sense. Where are you sourcing your tubes? As I've not yet got round to replacing the driver for the fluorescent unit, it may be worth using this as an opportunity for experiment. - but is it possible to use the old housing, or do I need to replace the whole shebang? The people offer a plug and play LED driver to replace the ballast, but it's obviously designed for 50Hz lights with the ballast you just plug into the side of the unit.


Gordon Tarling15/07/2017 10:07:16
147 forum posts
3 photos

Robin - these **LINK** are the tubes that I'm using. They don't require a driver, just a simple wiring modification to bypass the ballast. Diagram supplied with every tube. You may well have a TLC branch near you.

Andrew Tinsley15/07/2017 10:45:42
679 forum posts

Just a thought or two on LED lighting. I spent some time in the lighting industry and also did development work on LEDs at the beginning (40 odd years ago).

The one thing that some LED manufacturers don't tell you, is that the quoted lifetime of LED lighting refers to the lifetime of individual LEDs tested as individual units.

Now LED lifetime is critically dependent on temperature, so if you have LEDs in a group. Then the local temperature rises and down goes the LED life.

For example if you have an LED replacement bulb (like the old household lamp) and you put this in say a lamp shade that has no means of convection, then the bulb life is critically compromised. I have such reflectors and major brand LED light bulbs do no better than 1000 hours lifetime.

I have changed over to LED lighting and would not go back to GLS or compact fluorescent lamps. But beware of the smooth sales talk of the lighting manufacturers. You MUST keep the local temperature down otherwise the lifetimes are much reduced.


Robin Graham15/07/2017 23:26:35
361 forum posts
41 photos

Thanks for the link Gordon - no TLC branches near me (I'm in Derbyshire - they seem to be SE oriented), but presumably I can get similar things locally. Not found anything with that lumen/watt ratio yet though. Good to know they can be wired into standard housings, I think this may be the way to go.

Andrew - yes well aware of the hype, but the GLS bulbs I've replaced with LED's, whilst not lasting anywhere near quoted 'average life' have been cost effective. Interesting that temperature is critical. I'd assumed that it was the drivers that failed first but maybe not so?


Gordon Tarling16/07/2017 17:32:38
147 forum posts
3 photos

Robin - TLC will deliver.

Ian Hewson16/07/2017 17:55:47
161 forum posts
9 photos

Not flourescent they won't

Gordon Tarling17/07/2017 10:50:02
147 forum posts
3 photos

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.

Muzzer17/07/2017 12:43:38
2656 forum posts
437 photos

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.


duncan webster21/07/2017 23:37:00
1409 forum posts
20 photos

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?

clogs22/07/2017 07:57:44
352 forum posts
12 photos

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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