Look at lumens, not at watts. An old 36 watt T8 gives about 3,350 lumens, a 58 watt one around 5,240 lumens. Our 120 cm tube reaches 2,700 lumens at 18 watts and the 150 cm 3,625 lumens at 25 watts, so you give up a little light and a great deal of consumption.
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Why watts are not a measure
Watts are what a lamp draws, lumens are what comes out. With fluorescent the two were reasonably linked, so for years you could buy on wattage. With LED that ratio is a factor of three or more better, and then watts say nothing.
A 25 watt LED tube next to a 58 watt fluorescent is therefore not a halving of the light but of the consumption. The difference between the two units is in What is the difference between kelvin and lumens?
What the old tubes really gave
The Philips MASTER TL-D Super 80, for years the standard in Dutch commercial buildings, is listed in the data sheet at 3,350 lumens at 36 watts and 5,240 lumens at 58 watts, both in colour 840.
Then there is something that appears on no box. A conventional ballast burns about 10 watts of its own. So your 36 watt tube actually cost nearer 46 watts at the meter. That loss disappears the moment the ballast comes out.
And fluorescent declines. After thousands of burning hours a fluorescent tube gives noticeably less than on day one, so the tube you are replacing now probably stopped reaching its stated figure long ago. How that works with LED is in When does an LED lamp need replacing?
What our tubes put back
Four versions, two lengths.
- 120 cm adjustable: 12, 15 or 18 watts, at the highest setting 2,700 lumens at 150 lumens per watt.
- 120 cm high lumen: fixed 20 watts, 2,400 lumens, IP22.
- 150 cm adjustable: 18, 20 or 25 watts, at the highest setting 3,625 lumens at 145 lumens per watt.
- 150 cm high lumen: fixed 25 watts, 3,500 lumens, IP22.
Next to a fresh 36 watt fluorescent, 2,700 lumens is a loss of light on paper. In practice you rarely notice, for three reasons: the old tube is no longer fresh, LED throws its light downward rather than also up into the housing, and the reflective inside of an old fixture has usually gone dull.
If you really want the same amount of light
Then the honest answer is that a single tube will not match a fresh 58 watt at 5,240 lumens. Two options.
If there is a twin fluorescent batten, you replace both tubes and two times 3,625 lumens puts you comfortably above the old output, at 50 watts instead of well over 130.
Or you replace the whole fixture. An LED panel of 120 by 30 fits the same space as a twin fluorescent batten and gives 4,050 lumens out of 30 watts, with a valid CE marking and five years of warranty. The trade-off is on fluorescent to LED.
What it saves in electricity
Take a workshop with six 36 watt tubes burning eight hours a day. With the ballast that is about 46 watts each, so 276 watts in total. Over 250 working days of eight hours that comes to over 550 kWh.
Six LED tubes at 18 watts draw 108 watts and come to around 216 kWh. The difference is about 335 kWh a year. What that is in euros depends on your tariff, and What does LED lighting cost in electricity per year? works it out for you.
Before you order: the ballast has to come out, see How do you convert a fluorescent fixture to LED? The tubes are at LED tubes.
How many watts of LED replaces a 36 watt fluorescent?
Our 120 cm tube at 18 watts gives 2,700 lumens against about 3,350 lumens from a fresh 36 watt fluorescent. Counting the ballast, consumption goes from around 46 to 18 watts.
How many lumens does an old fluorescent tube give?
According to the data sheet for the Philips MASTER TL-D Super 80 in colour 840: 3,350 lumens at 36 watts and 5,240 lumens at 58 watts. A tube that has burned for years no longer reaches that.
Will I get less light after switching to LED?
On paper a little, in practice usually not. LED throws its light downward, while a fluorescent tube also shines up into the housing, and the old tube has already declined.