David Hansen explained :
Not having to replace the bulb so often. Reducing greenhouse gas
emissions.

On/off type of use is a killer for discharge type lights and they do
not achieve the full light output until a time after you would normally
be turning it off again.

You do not save much if any
energy if it is only turned on for a couple of minutes

One will indeed only save a little energy over the space of a few
minutes. However, little things add up over the years.

True, but you need to do the sums for what would be saved over the
years v the extra cost of the lamps and their reduced life from the
frequent switching.

and the
manufacturing process is not very green when compared to an ordinary
cheap filament lamp.

That would be a factor, if both types of bulb lasted for the same
time and used the same energy.

Discharge lamps only achieve economy once they have been turned on for
a while. I once saw the calculations for the short period use of a
fluorescent light versus an equivalent output filament lamp - taking in
all of the factors such as wear and tear, consumption, cost of labour
replacing etc.. The filament lamp proved to be more economic upto 1
hours use.

Before installing these types of energy saving lamps and flourescents,
I make a decision as to whether the extra expense is worth while for
the type of use the room receives. Economy is not always factored in,
because sometimes fluorescent provides a more suitable light to a
filament light. I have around 70' of fluorescent lighting in my garage,
this despite a small proportion being frequently switched, because this
type of lighting is more suitable for this type of use.

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Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk