South African lightbulbs tested — with no surprises

MyBroadband tested the power draw of incandescent, fluorescent, and LED light bulbs, and the results were in line with what the manufacturers promised on the box.

Modern LED lightbulbs promise bright light at a fraction of the power draw compared to older CFL and incandescent bulbs.

Old incandescent bulbs were commonly available with power ratings of 40W to 100W. Because of their high power draw, they are no longer widely used for illumination.

Incandescent bulbs were replaced with compact fluorescent (CFL) bulbs that need significantly less power and have a longer life.

CFL bulbs are commonly available with power ratings around 10W to 30W, yet still provide brightness on par with their incandescent counterparts.

Although CFL bulbs are far more efficient than incandescent bulbs, they are no match for LED bulbs which are now becoming the standard.

LED bulbs offer the same brightness as CFL bulbs but require far less power — between 3W to 15W.

LED bulbs also last much longer — 25,000 hours compared with 10,000 hours for CFL bulbs and 1,000 hours for incandescent bulbs.

These figures are all based on manufacturer claims, and to ensure we are not misled, MyBroadband decided to test the power consumption of different bulbs.

We tested different incandescent, fluorescent, and LED light bulbs with a PZEM-004T based monitoring system to see how they compare with the rated values.

The measurement module measures AC voltage, current, real power, frequency, and power factor with an accuracy of better than 1%.

We started with incandescent bulbs and found that they drew up to 17% less power than advertised.

It is easy to explain the lower power consumption. These bulbs are rated at 230V, 240V and 250V, while the actual voltage on the grid was closer to 220V at the time of testing.

These bulbs have no fancy circuitry to manage power draw and rely on Ohm’s law as they use a simple resistive element. Thus, as the voltage goes down, the current and power draw also decline.

The resistive nature of these bulbs was also confirmed by the perfect power factor of 1, indicating no capacitive or inductive components.

Although it took some time to settle at a constant draw, the CFL bulbs were closer to the advertised power draw.

The CFL bulbs make use of rectifying circuits inside, which means they change the current waveform relative to the voltage waveform, causing a drop in power factor.

Consumers generally only pay for real power consumed, ignoring this inefficiency, but this may play a role in some commercial setups.

The CFL bulbs’ power draw ranged between 4% more and 6% less than the advertised values.

The LED bulbs that were tested were the closest to their advertised values, drawing 2% and 3% more power than expected.

The LED bulbs make use of a lot of circuitry inside, causing a similar power factor to the CFL bulbs.

Judging by a simple side-by-side comparison and published brightness values for different bulbs related to power draw, LED is the way to go.

The table below provides an overview of the light bulb power draw test results.

Lightbulb Power Draw
Type Rated Power (W) Actual Power (W) Difference Power Factor Rated Luminous flux
PnP Compact Energy Saver CFL 14 14.6 4% 0.64 750 lm
PnP 9W LED T-lamp LED 9 9.3 3% 0.62 765 lm
PnP 5W LED T-lamp LED 5 5.1 2% 0.63 420 lm
Osram Energy Saver CFL 14 13.8 -1% 0.64 810 lm
PnP 18W BC CFL 18 17 -6% 0.65 990 lm
Philips 40W Candle Incandescent 40 37.5 -6% 1 400 lm
Generic 100W Incandescent Incandescent 100 86.8 -13% 1 1200 lm
Tungsram 40W Spherical Incandescent 40 33.3 -17% 1 400 lm

Now read: Fluorescent light bulb sales can be banned in South Africa

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South African lightbulbs tested — with no surprises