Have a pretty old twin 6 ft fitting (ballast and starter) where an original T12 tubes has failed. Replaced it with a T8 - which is very noticeably dimmer than the other old T12. Swapping them makes no difference, so not the control gear?
Blurb says they are more efficient than T12. Does that also mean less light?
Thought you of all people would have converted to LEDs by now, Dave!
They have a noticable run-up time, particularly when not used for a long time (e.g. when brand new). Leave them on for 10 mins, rather than comparing at initial switch-on.
(T12 also have a run-up time which is actually much longer, but the initial light output is not as low as with a T8.)
You thought very wrong.
The actual light is more important to me than just running costs.
Yes - I had noticed it gets brighter. But there is still an obvious difference between them even after an hour or so. It's not a real problem
- just annoying.
In cases where I have replaced a T12 with an T8 I can't say I had noticed it being dimmer... were they comparable wattage tubes?
Yes people are saying that leds are more piercing than the old tubes even when supposed to be the same colour temp. I still have tubes but then they do not get used much unless i have people round these days, no point!
It might be nice though to get shot of the buzzing chokes syndrome! Brian
So why might that be the case them? I'd have thought there would in fact be little difference unless the actual phosphor is different. Brian
You should be ashamed of yourself.
I think most T8 tubes nowdays are compact fluorescents, meaning they contain an amalgam pellet to regulate the mercury vapour pressure inside the tube. I doubt they can get the mercury dosing low enough otherwise. The tube and the amalgam pellet have to warm up to liberate the right amount of mercury for the tube to operate at the correct mercury vapour pressure. Also, it can take some minutes for the mercury vapour to diffuse along the full length of the tube - before that, the middle of the tube may be noticably dim as the gas fill which starts the discharge doesn't give off UV to excite the phosphor. This latter effect is very noticable when the tube hasn't been used for a long time.
The phosphor in T8 tubes is a tri-phosphor or poly-phosphor coating. The phosphor in T12 tubes is a halophosphate traditionally, although some of the last T12 tubes had switched to use tri-phosphor coatings, but that made them expensive as they need twice as much as a T8, and it's more expensive than halophosphate coatings anyway. However, this is not related to run-up times.
The bit about using an amalgam might be true in view of the higher wattage loadings on these 'small bore' tubes but it might just be due to using the absolute minimum of straight mercury vapour with whatever liquid reserve there is being adsorbed into the fluorescent coating which needs to warm up to liberate enough vapour for the tube to operate at full efficiency.
The loading may be higher but nowhere near that of a CFL tube which
*does* mandate the use of a mercury amalgam to improve high temperature efficiency which is slightly lower than that of a tube designed for lower temperature operation with a standard mercury fill - the slightly lower efficacy of a high temperature tube using an amalgam is far better than an ordinary tube operating at the same elevated temperature but it's a compromise in efficiency just the same so I'd be surprised if a mercury amalgam is used in a linear tube boasting improved efficiency over its earlier counterpart.The T8 tubes might be loaded slightly higher than their T12 predecessors but I wouldn't have thought so much as to warrant the use of a mercury amalgam for high temperature tubes or CFLs. Their improved efficiencies mitigate the temperature rise somewhat. For example a 4 foot fitting using even the older type of electronic ballasts that sacrificed tube life for 'instant start' (not quite as 'instant' (nor as kind to tube life) as the half century old Quickstart iron ballasts) only ever draw 36 watts with a T8 "36W" 4 foot tube compared to the quickstart ballasted fitting with a 4 foot T12 "40W" tube which draws 51 to 52 watts all told.
I don't know what a crappy switch start iron ballasted fitting draws since I've never had one on the workbench to test with my trusty Metrawatt analogue watt meter. However, my best guess would be around the 56 watt mark since there will still be some electrical heating of the tube filaments due to the tube current flowing via one filament pin at each end of the tube, the strength of which current will taper off to zero at the disconnected pin end of the filament which has to rely solely on electron bombardment heating alone.
The Quickstart transformer will provide about half the initial startup filament voltage after the tube strikes due, not to a voltage spike but to the copious supply of electrons given off by the filaments alone when they were receiving the full starting voltage prior to the tube striking. Since the quickstart transformer maintains half filament voltage which provides additional heat along the whole length of the filament to supplement the electron bombardment heating effect, the risk of sputtering emissive material from the cooler end of the filaments in the case of the cheap switch start ballasted fittings is eliminated, improving not only lamp life run times in continuous running tests but also reduced switch on sputtering loss making the quickstart not only gratifyingly quick to start up (250 to 300mS) but pretty well immune to switch on cycles wear out.
Unfortunately, compared to a modern electronic ballasted 4 foot T8 tubed fitting, this comes at a significant energy cost (51W versus 36W) which, with the lack of ready availability of Quickstart compatible tubes, means I have to put up with the 900ms delayed start of a modern, 'Tube Safe' Helvar reballasted B&Q electronic fluorescent fitting that had been cursed with a Chinese made (but of surprisingly high quality[1] - it didn't lack for filter capacitors to fill 'empty spaces') "Old Skool" tube destroying electronic ballast).
Not only do I have to put up with the 900ms delayed startup, I now also have to put up with the mobile pattern of dark and light bands one used to associate only with brand new T12 tubes during the first dozen or so hours of use before the mercury was properly spread along the whole tube length and its light output would reach its peak almost instantly on each subsequent switch on, unlike the modern T8 tubes which suffer this characteristic start up property indefinitely and take 5 to 10 minutes to eliminate the mobile pattern and finally come up to full brightness in the case of both a warm and a cool white tri-phosphor T8 tube.
TBH, considering the 33% reduction in energy consumption for the same or slightly larger amount of light, the 900ms startup delay is a tolerable sacrifice. It's this nonsense of protracted warm up times with modern T8 mercury starved tubes that irritates me the most. I guess, in whole, that it's the result of H&S going a step too far in satisfying the Greenwash brigade.
[1] If you could discount the 'Skoolboy Howler' mistake of running the tube end connection wires internal to the rectangular plastic extrusion housing the PCB, allowing the insulation to be melted by one of the switching transistor heatsink tabs which eventually caused the whole thing to go "PHUT!" (not a bang but enough to blow the safety fuse and probably a few other components as well) just after it started destroying the tube fitted less than 6 months earlier to replace the original tube that had lasted no more than 12 months and assumed to be of defective/ poor quality manufacture.Normally, I'd consider doing a repair on something like this but, in this particular case, I had absolutely no desire to give this item more chances at prematurely burning out tubes. The signs were all there to indicate that a straight repair would not be in my best interests - 300ms startup sequence at half illumination level with a 50 or 25 HZ flicker component, a plastic extrusion housing the PCB which relied on a couple of pieces of double sided adhesive tape, which I'd replaced with a single full length strip straight after running my commissioning tests, to hold it in place in the fitting.
I knew there were more modern microprocessor controlled electronic lamp ballasts that not only featured tube fault protection but also included some flexibility in adapting to different tube types as well as rejecting unsuitable/faulty tubes so I googled for suitable replacements and had that Helvar unit paid for and delivered for just under a fiver from Amazon.
I had hoped to be able to use the original and/or its replacement tube but the Helvar ballast refused to run them up so I had to take a chance on yet another tube purchase (from Toolstation this time). The warm white tube worked/s just fine but proved to be the wrong choice for a kitchen with pale lemon yellow walls, hence the second purchase of a cool white tube from Toolstation a couple of months later.
I'm an 'LED skeptic', ie I'm less than convinced they give a decent light output.
However, I recently replaced a 5' tube in the garage with an LED one from Screwfix and I'm very impressed. As far as I can tell by eye, the output is as good as the other tubes. It comes on instantly (all but). As for life time, it is early days. It was about £15. No rewiring, just replace the starter with a 'special' supplied (I suspect a fuse or short circuit).
Like you, I'm more bothered about light output but, unless I see a problem, I will replace the other tubes as they fail with similar LEDs.
I see the TLC ones are slightly cheaper. They *seem* to go straight into a magnetic ballast light, while you need to bypass an electronic ballast (OK not difficult, but more fiddly for high suspended fittings). Are there actually two (or more) types of LED tube, or have I missed something?
I'm not sure.
I only tried the LED option as the tube life in the garage was disappointing for no obvious reason. Other tubes in the house (since removed but only as part of an bathroom refit) lasted 20 years at least. The ones in the garage required frequent replacement.
It could be the fittings are designed for the older style tubes- they were already fitted when we bought the house.
For a DIY person isn't it more satisfying to remove any redundant components from a fitting when converting to LED? I think I would want to. At least rewire it.
Yes, I'd want to remove the ballast
Maybe not if its awkward to get at the luminaire.
That was migh thought - just leave the shell, but then if the only change is the new 'starter' for LED there's always the back-up plan of refitting the florrie.
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