Can anyone tell me what the point is at which it is better to leave a
38W fluorescent strip on to save electricity rather than turn it off
and then on again?
I can't help believing that the starting current can't draw a very big
load, so if you are away for a couple of minutes it makes sense to
turn the light off. BTW, I accept totally that start may reduce the
life of the tube, so we're not talking of saving money here :-)
From the energy consumtion perspective, you should turn the tube off
if you won't be using it for a few seconds. The high starting current
is (and has always been) a complete myth.
From the tube life perspective, it depends very heavily on the type
of control gear the tube has.
However, fluorescent lights do take a little while to reach full
brightness (especially if they are in a cold place such as a garage)
So turning them off will mean they will need a warm up period
(obviously the length of time they are off relates to the warm up time,
so in your case, a couple of minutes off will not require long unless
it is bloody cold (In witch case, fluorescent probably wouldn't be the
best choice anyway!)
If the initial brightness is sufficient, then turn them off, if not,
leave them on for those couple of minutes or so!)
I used to be taught the break even point was about 1.5 hours, for
consumption versus wear and and tear. That used to take into account
the cost of changing tubes, the labour involved and several other
I would suggest it is probably much less than this now, lets say 15
minutes. It takes a cold fitting almost this length of time anyway,
before it starts to produce full output.
I have have PIR triggered flourescent lights in my garage and these are
set to stay on for a minimum of 15 minutes.
Fls do take a higher current during start, but we're only talking 2 to
3x run current. The old leave em on thing is a myth. Repeated
switching does affect the life of the tube, but then so does leaving
them on, and that eats lectrickery. All in all if you dont need it
switch it off.
The old 4 pin thermal starters from the 1940s were slower operating
IIRC, so the start current continued longer, and this shortened the
life of the then scarce tubes, so there may have been something to it
If inadequate light when first on is an issue - ie in outdoor apps -
consider using the fatter tubes which suffer much less from this than
the modern thinner ones.
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