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Johnny B Good Johnny B Good is offline
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Default Them new-fangled flourescent lights

On Sun, 16 Sep 2018 16:11:54 +0000, Cursitor Doom wrote:

Gentlemen,

Back in the 1960s, when tubes were coming into service more and more, it
was a widely held belief that they were more expensive to run than
tungsten filament bulbs if turned on for short periods. It was said that
most of the power they consumed was drawn during the 'strike-up' phase
so if they weren't on for at *least* an hour, you might as well be using
TF bulbs.
Well, here we are 50+ years on and tubes are now very much old tech.
What, with the benefit of hindsight, have the Panel to say about those
old efficiency claims of the day?

Just curious.....


There was *some* justification for that belief but it wasn't electricity
costs, it was premature wear of the thoriated cathode filaments due to
the use of the cheap 'n' nasty switch starter.

Fluorescent lamps are discharge lamps which, in common with all lamps of
that class, have a negative impedance characteristic which needs to be
swamped out with a positive impedance wired in series. Their efficiency
was so much better than the incandescent filament lamps they replaced
that even with the losses of a resistive ballast on a 230vdc supply, they
still gave off two or three times more light of a tungsten filament lamp.

However on AC supplies, it became possible to replace the ballast
resistor with a ballast choke to provide a much less lossy positive
impedance. The only downside being the inductive (lagging) current
component this added to the load on the mains supply which increased the
wattless amperage which, as far as the PSUs were concerned weren't
wattless when it came to the I squared R losses in their transmission
lines.

The solution was to mandate that a power factor correction capacitor be
wired across the mains input of each light fitting using a tube with a
rating higher than 20W in order to reduce this inductive loading to an
acceptable level.

The filaments in fluorescent tubes were designed to run at full heat
from the short circuit current of the ballast choke so that a simple neon
heated bi-metallic switch could be used across the lamp as a crude
starter. It worked but at great cost to tube life when used in frequently
switched service.

When such lamps were only switched once or twice a day, there was no
point in upgrading to a "Quickstart"(tm) transformer to give flicker free
almost instant reliable wear free starting that would let you treat it
like an ordinary filament lamp and still get the 7 to 12 thousand rated
hours of life before it dropped to the 80% of design lumens point deemed
to be the most economic point at which to replace it (generally several
thousands of hours before it would actually fail to fire up properly).

Rather annoyingly, the newer T8 reduced mercury fill lamps will no
longer fire up on a Quickstart ballast. For me, that meant shelling out
on an electronically ballasted fitting from B&Q when the missus insisted
on my replacing the older fluorescent fitting in our kitchen after we'd
had the ceiling repaired post flat roof leak.

Unfortunately the B&Q fitting turned out to have been cursed with a
'Dumb' Chinese made ballast which caused the T8 lamps to fail faster than
the old fashioned switch started units used to, simply on account of the
fragility of "modern" inadequately dosed with mercury T8 "high
efficiency" tubes due to the aggressive 'instant start' characteristic of
the 'dumb' electronic ballast.

Luckily, the ballast failed about 18 months and two lamps later, forcing
me to buy a proper microprocessor controlled replacement (about £4.70
delivered) which finally put paid to the problem of short tube life.
Although I'm resigned to the unimpressive 900ms start up time (flicker
free mind!), it seems we've paid a high price for our high efficiency,
inadequately mercury dosed fluorescent tubes when I recall the 300ms
startup and extremely long life of the older adequately mercury dosed T12
tubes of yesteryear running on Quickstart ballasts.

I know that fluorescent lighting is obsolescent technology biding its
time for decent (and cost effective) LED based linear tubes to become
worth investing in as an upgrade in areas where a diffuse source of
bright lighting is required without having to go to the expense and faff
of fitting LED ceiling panel luminaires, hence my replacing the ballast
to carry on using the existing fluorescent lamp fitting in our kitchen.

Eventually, we might finally start to see 200LPW (more reliable) LED
ceiling panels making an appearance in the next 5 to 7 years. I reckon I
will have finally made my ROI on the existing light fitting just about
then. :-)

--
Johnny B Good