Electrical power vs. luminous efficacy of LED tubes
The electrical power of an LED tube, expressed in watts (W), indicates the energy consumed at any given moment to run it. However, this power does not directly reflect the amount of light emitted. To assess light output relative to consumption, we use luminous efficacy (expressed in lumens per watt, lm/W). High efficacy means a lamp produces a lot of light for every watt it consumes.
- Standard fluorescent tubes: efficacy of around 70 to 90 lm/W for the best tubes, often around 50 to 60 lm/W for older models.
- Modern LED tubes: typical efficacy of 100 to 150 lm/W, reaching ~160 lm/W on the highest-performing models.
In practice, this means that for the same brightness, an LED tube needs much less power than a fluorescent tube. In other words, an LED tube uses far less energy to produce the same light intensity. For example, an old 36 W fluorescent tube can be replaced by an 18 W LED tube with no loss of light. This gain in efficiency has an immediate impact on electricity consumption: an LED tube is estimated to use 50% (or even up to 60 to 70%) less energy than an equivalent fluorescent tube.
Consumption by LED tube length
An LED tube's consumption depends mainly on its length (and the number of LEDs it contains) and on its luminous efficacy. LED tubes come in several standard sizes, with power ratings proportional to their size. The table below shows typical power ranges for common LED tubes:
| LED tube length | Typical power (W) |
|---|---|
| 30 cm LED tube | ~3.4 W |
| 60 cm LED tube | ~6 W to 9 W |
| 90 cm LED tube | ~9 W to 14 W |
| 120 cm LED tube | ~12 W to 18 W |
| 150 cm LED tube | ~16 W to 25 W |
Indicative power ranges for general-purpose LED tubes, with luminous efficacy varying by model (from ~100 to 160 lm/W).
The longest LED tubes do consume more watts than the short ones, but they remain very economical compared with the fittings they replace.
- For example, a 120 cm LED tube generally uses between 12 and 18 W, whereas a traditional fluorescent tube of the same length typically uses around 36 W (not counting any ballast losses).
- Likewise, a 150 cm LED tube only uses around 16 to 25 W, compared with ~58 W for its older fluorescent equivalent.
The greater the length, the larger the absolute energy saving compared with the old fluorescent tube, while providing equivalent lighting.
Comparison: LED tube vs. fluorescent tube
It is useful to compare the consumption of an LED tube directly with that of a traditional fluorescent tube of the same size. The following table illustrates this comparison for different common sizes:
| Length | Fluorescent tube (W) ≈ | LED tube (W) ≈ | Energy saving |
|---|---|---|---|
| 60 cm | ~18 W | ~7 W (6 to 9 W) | ≈ 60% less |
| 90 cm | ~30 W | ~12 W (9 to 14 W) | ≈ 60% less |
| 120 cm | ~36 W | ~15 W (12 to 18 W) | ≈ 55% less |
| 150 cm | ~58 W | ~20 W (16 to 25 W) | ≈ 65% less |
On average, electricity consumption is cut by around half or more when switching from fluorescent to LED lighting. In each case, the LED tube needs far fewer watts for the same length, thanks to its better luminous efficacy.
Good to know
As well as lower consumption, LED tubes offer other benefits (instant start, no flicker, no mercury, longer lifespan). However, these aspects go beyond electricity consumption and will not be covered in detail here.
Calculating the annual consumption of an LED tube
The consumption of a tube (or batten) is measured in kilowatt-hours (kWh). Here is a simple method for estimating it over a year.
Calculation method
- Daily consumption (kWh/day) = (Power in W ÷ 1000) × hours of use per day.
- Annual consumption (kWh/year) = daily consumption × number of days of use (often 365 for daily use).
Example
Take an 18 W LED tube used for an average of 5 h/day all year round:
- Daily: (18 ÷ 1000) × 5 = 0.09 kWh/day
- Annual: 0.09 × 365 ≈ 32.85 kWh/year
Comparison with a 36 W fluorescent tube
- Daily: (36 ÷ 1000) × 5 = 0.18 kWh/day
- Annual: 0.18 × 365 ≈ 65.7 kWh/year
- LED saving in this example: around 50% less energy (32.85 vs 65.7 kWh/year).
- At €0.20/kWh: ~€6.57/year (LED) compared with ~€13.14/year (fluorescent).
Good to know
If the lights are on for longer (e.g. professional premises at 8 h/day), the annual gap grows even wider. A ~20 W LED tube uses around ≈ 58 kWh/year, while a fluorescent tube with equivalent output approaches ≈ 115 to 120 kWh/year. Across an installation of several tubes, the cumulative saving becomes very significant.
In short, an LED tube uses very little electricity compared with old fluorescent lamps. Thanks to high luminous efficacy (more lumens per watt) and much lower power for the same brightness, LED tubes deliver 50 to 70% energy savings on lighting. Knowing the wattage of these LED tubes and calculating their annual consumption in kWh helps you appreciate the savings that can be made every day. For homes and businesses alike, switching to LED tubes means lower electricity consumption with no compromise on lighting, which benefits both your energy bill and the environment in the long term.
