The Christmas Lights Nightmare
When
replacing blown
bulbs
in
your
Christmas tree lights its
important to match both the
voltage and power rating of the
bulbs as if you do not either the bulb will
fail quickly or worse still all the other bulbs in
the string will see too much voltage and current
(power) and burn out quickly. To get the correct
voltage divide 240V or 220V by the number of lamps in the
string for a direct mains powered string or 24V by the number for
24V powered strings etc. Read the total voltage from the transformer
(that black or green box) and use that figure. Also bear in mind that low
voltage strings often have more than one parallel circuit, I have one 24V set
with two parallel 16 x 1.5V bulb strings on each of four colours. Its easy to check remove one of the bulbs and see if that whole circuit goes out or half of them or a third
etc. You will need to round the calculated value to the nearest ½ volt. The current or power
rating is more difficult although fortunately most have only one power rating per voltage. Notably
5V bulbs (50 bulb sets) are available in 0.45/0.5W and 0.7W versions and although the 0.45W &
0.5W bulbs can be mixed you cannot mix the 0.7W ones with them. If you do the 0.7W ones
glow dimly and the 0.5W ones glow extra brightly and will burn out prematurely. One final
hint, when fault finding bulbs take them out one by one and test them for continuity with
the resistance setting of a cheap multimeter (or an expensive one if you prefer)
before replacing it in the fitting or fitting a new one if its blown. Each bulb
should measure as few ohms but NOT a dead short (0 ohms). The blind
swapping technique favoured historically is great for finding one
blown bulb but if you have more than one failed in the string its
VERY slow! The testing method is slower for one failed bulb
but MUCH faster for multiple failures. Some sets seem
to be prone to multiple failures whether through
poor storage conditions or knock-on effects
when one bulb blows I do not know. Good
luck and remember its much more
environmentally responsible to
replace bulbs in your existing
sets than you go out
and buy new ones!
Happy
Christmas!