Eight Foot Long Fluorescent Fitting. Calling All Old Sparks.

mapj1:

Have you got that the right way round ? I  thought the 125s in the 40mm diameter were being phased out in favour of the thinner ones at 100W

125 phased out

   100  pricey


I'd expect either to be tricky to get on  delivery and to cost more than a new fitting to be honest - how old is it and what sort of ballast?


Either will light in the other fittings, but may be a bit slow on the striking, i suspect it voids the warranty, but my experience is that it that the lamp life is not much affected. Far more important to lamp life is electronic vs traditional ballast.

According to the data-sheets, the running voltages are similar.


Edit if trying to get near obsolete tubes from afar, beware of tubes made for the US market with a much lower striking voltage.

Mike.

Details. Old existing 8 ft. twin switch start fitting. Existing tubes 100W rated worn out. New fat tubes available from old stock are 125 W.


Z.

broadgage:

Many years ago, the common wattage of an 8 foot fluorescent lamp was 125 watts. Then in IIRC the 1970s a 100 watt 8 foot tube was introduced, intended to absorb about 100 watts in an existing fitting with an existing 125 watt ballast. The ACTUAL power absorbed by a 100 watt lamp on a 125 watt ballast varied a bit according to mains voltage, ambient temperature and component tolerances. It tended to average about 105 watts.


If you have a fitting with a 125 watt ballast, then either 100 watt or 125  watt lamps may be used without concern.


Later,  new 8 foot fittings were introduced with a ballast intended for the new 100 watt lamps. The ACTUAL wattage absorbed by a 100 watt lamp in one of these fittings also varied according to line voltage, temperature, and component tolerances, but tended to average about 95 watts.

If you have one of these slightly newer fittings intended for 100 watt lamps, then it wont reliably and correctly run a 125 watt lamp.

A 125 watt lamp on a 100 watt ballast MIGHT work under optimum conditions but might fail to start reliably at low temperatures or line voltage.

Thank you broadgage, I suspected that you would know the answer. I shall try to get more info and report back. The problem that I have found with old ballasts is that the electrical details printed on them can be burnt off due to the operational heat, and the details lost. If the old fitting is in the customer's house starting of the flu. should be o.k. If it is in an unheated garage problems may result in starting.


Z.

Kelly Marie Angel:

I have an 8 foot flu in my kitchen have noticed it does occasionally struggle to strike especially if its chilly in warmer conditions it starts with little effort. I think very old 8 foot fittings had a series condenser between choke and mains if this loses its value it will effect starting. Thankfully my kitchen one is a bit more modern  so just has a choke  and starter of course. One interesting odd thing I've noticed is that the twin 4 foot 36 watt tubes in my workshop are dim and flickery when cold but the high frequency tube on the other side of the shop don't flicker with the cold just an observation

I have just found my old pocket book entitled "3rd Year Electrical Installation Practice" by H.A. Miller. It has a wonderful detailed section on lighting and shows many different fluorescent circuits for single tubes and twin short tubes. One circuit does indeed show a single 8 foot tube with a choke and capacitor in series along with a starter. I suspect that in old fittings the capacitor will be the weak link in the chain. I do carry the 125 W fluorescent starter units as well as the 4 to 65 Watt type. I rarely use the former these days. I suspect that replacement capacitors are expensive.


Z.