Electrical Engineering and Environmental Engineering
Introduction
Purpose
The purpose of this report is to recommend that best way to save energy used for lighting by evaluating the best time to turn off a light based on the type of lighting used.
Problem
Energy costs are important to lower in order to save on the family budget as well as to decrease the amount of pollution entering the environment. Turning of the lights when a room is not in use has always been a good way of saving energy when incandescent lighting was in general use. A variety of lighting designs are available in contemporary times. Those include halogen lights, compact fluorescent lamps (CFLs), and light emitting diodes (LEDs). In order to determine the most efficient energy savings two variables need to be evaluated and compared (a) the type of lighting and (b) the best time to turn off the lights. CFLs and LEDs are far more efficient than incandescent lighting but another question remains. Is more energy used the more often the newer types of light bulbs are switched on and off? In order to determine the answer to this question the rated operating life of each light bulb needs to be evaluated with reference to the number of times the light bulb is turned on and turned off.
Generally the average life of a bulb is calculated when 50% of bulbs that had been installed at the same time are still in operation. Two types of ratings are often meant when the phrase rated operating life is used (a) rated life and (b) economic life. Rated life refers to the manufacturers published rating considered when the bulbs are burned in a vertical position. Economic life of a light bulb is usually considered to be close to 60% of the rated life. The economic life is considered to be the hours of optimum light output during the operation of the lamp and includes optimum aesthetic quality and optimum energy consumption. The economic life is therefore more accurate because at optimum lighting levels, no lighting power depreciation or loss in efficiency has occurred. On the other hand during the rated life, values in lighting power, colors and effectiveness have all started decreasing at about 60% of the life duration of the bulb.
Another variable that has a great impact on the average operating life of a light bulb is the burning position. A light bulb held in an upright position at a 90° angle to the floor therefore have been shown to have a longer life expectancy than bulbs burned while in a horizontal position. In fact the rated operating life for a bulb used in a horizontal position is considered to be only 75% of the same bulb held in an upright position. (Lamp, 2013)
Finally the cost of the energy is a crucial factor in determining the best time to turn lights off when no one will remain in a room.
Scope
A recommendation has been made as whether incandescent, halogen, CFL and LED lighting will save more money if they are turned off every time a room is empty. The amount of current at the time of turning on a light and turning off a light has been discussed. An example for calculating energy savings is included. Other ways to save energy costs for lighting have been briefly reviewed.
Discussion
Accuracy
Explanation
Accuracy is important to calculate when attempting to create strategies for energy savings. The term ‘accuracy’ is a description of the relative precision of the resulting data after calculations have been made. In order to make a practical recommendation some assumptions need to be made. The first is that the economic operating rate will give better results because the optimum light is considered before depreciation of the lighting values has begun. Secondly an assumption is made that for this recommendation all the bulbs will be operated in the vertical position.
Light Bulb Types and Characteristics
Explanation
Incandescent bulbs do not use energy efficiently so they need to be turned off whenever leaving a room. Ninety percent of energy used by incandescent bulbs dissipates into the air as heat; leaving only 10 percent of the energy to be used for lighting.
Halogen lighting are more energy efficient than incandescent bulbs but they are much less efficient than CFLs and LEDs. Therefore the best strategy for halogen lighting is to turn off the lights when they are not needed.
CFLs are energy efficient so automatically turning off a light and turning it back on when returning after fifteen minutes or less may not be the best strategy. The US Department of Energy (DOE) suggests if you leave a room but return within 15 minutes do not turn off the light. On the other hand if you leave the room empty for more that 15 minutes turn off the lights. ENERGY STAR™ CFLs are designed to withstand frequent switching from on to off.
LEDs energy costs are not affected by turning the lights on or off. Table 1 shows that a 12 watt LED bulb saves approximately 75to 80 percent in costs compared to a 60 watt incandescent bulb that shows no savings and a 43 watt energy incandescent bulb that shows only a 25 percent energy cost savings. According to Table 1 the 12 watt LED has the lowest annual energy cost ($1.00) and the longest bulb life (25,000 hours) compared to either of the incandescent bulbs and to the 15 watt CFL bulb.
Energy Saving Calculation
The first step is to calculate the amount of energy consumed when the bulb is burning. A 40 watt bulb uses 40 watts of energy per hour. 40 watts is equal to 0.04 kW so when a 40 watt light has been left on for one hour it uses 0.04 kilo watt hours (kWh). When a light has been turned off for one hour a savings can be assumed of 0.04 kWh. The amount you pay for energy each month is written on your monthly energy bill; find the amount you are charge per kWh. The kWh charges during peak hours and during non-peak hours should be on the bill.
If
(Rate per kWh) multiplied by (electricity saved) = value of the savings
and
rate/kWh = 10 cents and kWh = 0.04,
then
(10cents/kWh) multiplied by (0.04 kWh) = 0.4 cents.
The higher the wattage of the bulb the more energy will be saved.
Other energy saving strategies
Briefly other strategies for decreasing energy costs are the use of sensors (particularly with LEDs), timing controls, and manual strategies like pulling the drapes closed for insulation from sun or cold.
Conclusion
Summary
Incandescent lighting needs to be turned off whenever it is not needed because it is the least efficient type of lighting. Halogen bulbs should be treated the same way as the incandescent lighting because although more efficient their efficiency rate is not very high. CFLs should be left on if the time the room will be empty is fifteen minutes or less; a room left empty for more than 15 minutes should have the CFL switched off. LED lighting is not affected by switching the electricity on and off so this type of lighting would be the easiest to use. Coupled with other devices such as sensors and timers the energy cost for using LEDs will decrease further.
Conclusions
The incandescent and halogen bulbs should always be turned off when no one is using the lighting for the least amount in energy costs. The CFL bulbs need to be switched off when the room is left empty for more than 15 minutes. LEDs are unaffected by switching the electricity on and off. The efficiency of LEDs can also be enhanced by using sensors. Lighting devices such as timers and manually opening/closing drapes and shades (as appropriate) will also decrease energy costs.
Recommendations
Calculating the energy savings or energy gains by the lighting use behaviours of your family members will help everyone understand the difference made by using lighting responsibly. This report has demonstrated that keeping the lighting off when no one is in the room is a good way of saving money on energy especially if you are using incandescent or halogen lighting. Using CFL in your home is a good strategy but family members will need to learn a new habit: if they leave a room for 15 minutes or less the light can be left on but otherwise to gain the most in energy savings the CFL lights need to be switched off. Other ways of saving energy with devices or new habits in home management should be explored to save even more money on energy and essentially – to save energy.
Sources
“Lamp Life.” (2013). Venture Lighting, available from http://www.venturelighting.com/TechCenter/Lamps/lamp_life.htm
“When to Turn Off Your Lights” (2012 Aug. 30) The United States Department of Energy (DOE), available from http://energy.gov/energysaver/articles/when-turn-your-lights
