Saving electricity – LED lamps, air conditioning and tiered billing
Design & TechnologyElectrical Engineering & SafetyAges 17–18
Use it with your class: students open it from a link or a QR code, with no account needed.
Next in Electrical Engineering & Safety
A house has a bank of lights and an air conditioner: choose incandescent, compact fluorescent or LED lamps for the same 800 lm output, set the daily hours of use and the AC temperature, then click Run to watch the meter spin and energy build up over 30 days. The display shows energy A = P·t, the electricity bill under tiered pricing, and the CO₂ emitted; a bar chart compares the three lamp types and shows how much an LED saves.
Lesson: Saving electricity at home: choosing efficient appliances, using them sensibly, and computing energy use and cost
What it shows
The electrical energy an appliance uses is A = P·t, measured in kilowatt-hours. Lamps giving the same light output can draw very different power because their luminous efficacy differs: about 13 lm/W for an incandescent bulb, 55 lm/W for a compact fluorescent lamp and 100 lm/W for an LED, with the rest of the input turned into heat. For the air conditioner, each degree higher on the thermostat saves about 5% of its energy in this model. With tiered pricing the upper tiers cost more per kWh, so cutting use lowers the bill and the CO₂ emitted by generation.
How to use
Set the Lamp type, Number of lamps in the house and Lit hours per day, then the AC thermostat setting and AC hours per day, and press Run 30 days to watch the meter build up a month of energy. Read the lighting and air-conditioning energy, the bill and the CO₂ separately. Repeat with LED lamps, then raise the thermostat a few degrees, comparing the totals and the bar chart of the three lamp types.
Parameters you can change
- Lamp type (same 800 lm output) Incandescent bulb 60 W (13 lm/W), Compact fluorescent lamp 15 W (55 lm/W), LED lamp 8 W (100 lm/W)
- Number of lamps in the house 1–20 lamps
- Lit hours per day 1–12 h
- AC thermostat setting 22–30 °C
- AC hours per day 0–12 h
Questions to explore
- What percentage of lighting energy does switching from incandescent to LED lamps save over a month?
- In your settings, which uses more energy, the lighting or the air conditioner, and what should be changed first?
- How much does raising the thermostat from 24 °C to 27 °C change the monthly energy and bill?
