Dave Plowman wrote:

In article ,
Dave Gibson wrote:

Also bear in mind that the main cost is that of the electricity
used, not the bulb. Using a shorter life bulb may give you higher
light output and enable use of fewer or lower wattage lamps, which
will make a much more significant cost reduction than the difference
in bulb prices.


WTF?
50W is 50W in my book!


That's the energy consumed - nothing to do with the light output. Look at
fluorescents etc to see the difference between the two. And closer to
home, car headlight bulbs vary in light output dramatically for the same
power consumption.


Average lightbulb is around 1-2%.efficient. Halogen being at the upper
end, and cheapo dim long lifers at the other.

However the eye perceives brightness logarithmically. To be twice as
brght probably means 4-10 times the power. That makes efficiencty
variations of even 2:1 pretty insignifiocant.



1000hrs at 50W costs about £3.00 at 6p per kWh.
2000hrs at 50W costs about £6.00.


Yes, but the light output is also a factor, which you've omitted.


Its pretty irrelevant, as I have indicated.




Also the GU10's that come *complete* with the fitting I reckon have an
average life of 200hrs or less.


Dunno about that. It will depend on other things.



yeah. Right. Yawn.