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Default T12 & T8 tubes

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?

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Default T12 & T8 tubes

On Sat, 10 Feb 2018 13:16:54 +0000, Dave Plowman (News) wrote:

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!



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Default T12 & T8 tubes

In article ,
"Dave Plowman (News)" writes:
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?


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.)

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Default T12 & T8 tubes

In article ,
Cursitor Doom wrote:
On Sat, 10 Feb 2018 13:16:54 +0000, Dave Plowman (News) wrote:


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!


You thought very wrong.

The actual light is more important to me than just running costs.

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Default T12 & T8 tubes

In article ,
Andrew Gabriel wrote:
In article ,
"Dave Plowman (News)" writes:
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?


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.)


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.

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Default T12 & T8 tubes

On 10/02/2018 13:16, Dave Plowman (News) wrote:
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?


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?


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Default T12 & T8 tubes

On Sat, 10 Feb 2018 16:01:53 +0000, Dave Plowman (News) wrote:

You thought very wrong.

The actual light is more important to me than just running costs.


You should be ashamed of yourself.



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Default T12 & T8 tubes

In article ,
"Brian Gaff" writes:
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.


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.

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Default T12 & T8 tubes

On Sun, 11 Feb 2018 16:46:00 +0000, Andrew Gabriel wrote:

In article ,
"Brian Gaff" writes:
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.


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.

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On 10/02/2018 16:01, Dave Plowman (News) wrote:
In article ,
Cursitor Doom wrote:
On Sat, 10 Feb 2018 13:16:54 +0000, Dave Plowman (News) wrote:


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!


You thought very wrong.

The actual light is more important to me than just running costs.


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.


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On 15/08/2018 11:51, Brian Reay wrote:


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?
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On 15/08/2018 12:12, newshound wrote:
On 15/08/2018 11:51, Brian Reay wrote:


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.

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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.


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DerbyBorn wrote:

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.


Yes, I'd want to remove the ballast
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"DerbyBorn" wrote in message
2.236...



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.


Maybe not if its awkward to get at the luminaire.

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On Thu, 16 Aug 2018 19:27:34 GMT, DerbyBorn wrote:



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.


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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