We had 4 x 36W Fluorescent lamps (120cm) in a kitchen.

We replaced them with 4 x 18W LED lamps.

This was the Fluorescent choke for the old lamps:


Question: how much power did the original Fluorescent lamps consume?

My hint: 4 x 36W = 144W + does the choke consume some watts? I read that it could easily consume 4 x 30W. So could it be that the original setup costed them 264W/hour?

UPDATE: we just want the power consumption of the old "ballast and the starter" and the old fluorescent lamps together, so we can know how much less does a LED operation costs.

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    \$\begingroup\$ Watts per hour is not a useful measure for anything I've encountered, though it has been pointed out that it is sometimes used to describe a power plant ramp up behaviour. (using units correctly is immensely helpful, that is why I really don't like to see Watts/hour) \$\endgroup\$
    – Arsenal
    Nov 3, 2015 at 10:19
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    \$\begingroup\$ Choke (ballast) will consume some power - maybe 10-20% of the power of the lamps or 14-30W in your example. Consider how hot it would get if it consumed 120W! It would need special cooling provisions, which it doesn't have. \$\endgroup\$ Nov 3, 2015 at 10:48

2 Answers 2


It's hard to find actual usable data on the ballast you posted.

Wikipedia suggests that for reactive ballasts (like the one you used) the wasted power is in the order of 5-25% of the rated wattage of the lamp.

A paper from General Electric: Fluorescent Lamps Technical Bulletin TP 111R is cited to state that the loss of the ballast is around 10% of the lamps input power (dated 1978, haven't found a digital copy).

So the numbers I found do not support your claim of nearly 100% losses of the rated power in the ballast (have you got a source for that?).

In your case that would be between 7.2 W to 36 W, with a small emphasis on 16 W because of the cited paper. Total power: 151,2 W to 180 W (160 W emphasis)

In a not compensated ballast the power factor will be very bad. On the label you have a lambda given with 0.48 to 0.52. So you can get a VA rating (apparent power) which is double of the lamps W rating (active power), but that's not what you pay for usually.


Your power consumption will be roughly cut in half .This is because the efficiency of the string driver is in the same ballpark as the ballast it replaced .Your LEDs are more efficient than the flouros so basicly that is where you are getting your power savings from.String driver efficiency varies from about 70% to about 95% .


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