FAQ
TL;DR: Tests show a 230 V “4 W” LED bulb actually draws 3.8 – 4.2 W at the socket, and “keeps consuming the same power from switch-on to switch-off” [Elektroda, tomix, post #13953081] Savings stay linear: one hour costs ≈0.004 kWh; cheap mis-labelled lamps can gulp 9 – 22 W [Elektroda, jmar, post #16026881]
Why it matters: Knowing real wattage lets you predict bills, spot fakes and choose the right replacement.
Quick Facts
• Typical luminous efficacy: 80 – 110 lm/W for A-type LEDs [DOE, 2023]
• EU ‘4 W’ lamps must emit ≥320 lm (60 lm/W) [EU Reg.2019/2020]
• Full brightness time: <0.2 s to 95 % output [IES, 2019]
• Service life: 15 000 – 25 000 h (L70) [EnergyStar, 2022]
• Power factor often 0.5–0.9; households pay only active energy [Elektroda, Anonymous, post #15978684]
Do LED bulbs draw more power during warm-up like fluorescents?
No. Integrated 230 V LED lamps reach steady power in milliseconds and stay there; no warm-up surge occurs [Elektroda, tomix, post #13953081]
Will frequent on/off cycling change a 4 W LED’s energy use?
Energy depends on total lit time only. Switching 60 times an hour adds <0.01 % extra because drivers have negligible inrush charge [Elektroda, Anonymous, post #13953326]
How much does running one 4 W LED cost per year?
At 0.30 €/kWh, burning 4 W for 3 h/day uses 4 W × 1095 h = 4.38 kWh ≈ 1.31 € a year (3 h × 365) [kWh Calculator].
Why do some ‘4 W’ lamps feel hot and show 9 – 22 W on meters?
Cheap imports list diode power only; their inefficient drivers waste extra watts. One sample marked 4 W drew 9.4 W, another 22.3 W [Elektroda, jmar, post #16026881]
Am I billed for reactive energy from low power-factor LEDs?
Residential meters in most countries record active energy only; reactive kVarh charges apply to large commercial users [Elektroda, Anonymous, post #15978684]
Can a 4 W LED really replace a 35 W halogen?
Not in raw lumens (≈200 lm vs 550 lm). Users report subjective parity only in narrow-beam spots [Elektroda, e-sparks, post #13955652] Aim for 7–8 W LED when swapping 35 W halogens (≥500 lm).
Does voltage matter for power draw?
12 V LEDs need an external driver; total draw = lamp + driver losses. Integrated 230 V models already include this and the package wattage reflects mains draw [Elektroda, Anonymous, post #15967940]
How do I measure real wattage at home?
- Plug a certified plug-in wattmeter into the wall.
- Insert the LED lamp or fixture.
- Read ‘W’ after 30 s stabilisation. This shows active power, including driver loss. "Use a meter, not amperage math" [Elektroda, retrofood, post #16028225]
My room has bright spots and dark corners—why?
Many LEDs use small lenses giving 30 – 60° beams. Choose SMD models with frosted globes; they spread light over 120 ° and improve uniformity [Elektroda, ubidragon, post #13954404]
Do LEDs lose brightness over time?
Yes. Expect 70 % of initial output after 15 000–25 000 h (L70). Excess heat can cut this to 10 000 h; keep fixtures ventilated [EnergyStar, 2022].
Edge case: can a 4 W LED overheat and fail?
If a mislabeled lamp really dissipates 10 W inside a closed shade, junction temperature can exceed 125 °C and the driver may burn out within months [Elektroda, jmar, post #16026934]
What standards govern LED labeling in the EU?
Regulation 2019/2020 mandates stating total mains power, lumens, and energy class on packaging; hidden diode-only wattage violates compliance [EU Reg.2019/2020].