Article 4, Be Smart about Buying Light Bulbs–Get LEDs

BE SMART ABOUT BUYING LIGHT BULBS–GET LEDs

In 2012 the US Energy Information Administration estimated that residential lighting consumed 186 billion kilowatt-hours (kWh) or about 14% of all residential electricity.  This is a tremendous amount of energy.  In 2012 it’s likely that many, if not most, people still used incandescent light bulbs for home lighting.

Things are changing.  The old incandescent light bulbs everyone knows are giving way to compact fluorescent lamps (CFLs) and light-emitting diodes (LEDs).  These new bulbs provide the same amount of light as incandescents but use 75 to 85% less power and last much longer.  Incorporating them into your home means drastically reduced lighting costs for you and significantly reduced carbon dioxide (CO2) emissions for the environment.  CO2 is a greenhouse gas believed mainly responsible for global warming. 

SELECTING REPLACEMENT BULBS

To make good replacement decisions you’ll need to know the amount of visible light the bulb alternatives put out (lumens) and the amounts of power they draw (watts).  Table 1 can help.

Table 1.  Visible Light Output vs. Power Draw
       
  Power draw, watts
  Incan-  
Visible light output, lumens descent CFL LED
450 40 9 – 11 6 – 8
800 60 13 -15 9 – 12
1,100 75 18 – 20 13 – 16
1,600 100 24 – 28 18 – 22
2,400 150 30 – 52 25 -28


Let’s assume you want to replace a 60-watt incandescent (which emits 800 lumens of visible light) with a CFL or LED that provides the same amount of light.  Looking at the table you’ll see a 60-watt incandescent puts out about 800 lumens.  A CFL emitting the same amount of light draws 13 – 15 watts.  A LED draws 9 -12 watts. Generally, CFLs and LEDs draw about 25% and 20%, respectively, of the power drawn by incandescents.  It’s clear that their widespread use could put a serious dent in the 186 billion kwh load mentioned above.

OTHER IMPORTANT BULB CHARACTERISTICS

Long life is the most striking feature of the new bulbs.  Table 2 shows that CFLs last about 10 times longer than incandescents and LEDs 25 to 50 times longer.  You may not have to replace an LED bulb in your lifetime!  Here are a few cautions about CFLs.  CFLs contain small amounts of mercury and must be disposed of in hazardous waste facilities.  Rapid on/off/on cycling (< 5 minutes) may reduce CFL life drastically.  CFLs take a minute or so to attain full brightness, and their glass is easily broken, like the glass of incandescents. LEDs have none of these drawbacks. 

Table 2.  Other Important Bulb Characteristics
         
  Incan-    
Parameter descent CFL LED Comment
Bulb life, years 0.5 – 0.7 4-10 17-35 Assumed use 4 hrs/day
Hazardous disposal needed? No Yes No
Sensitive to on/off cycling? Some Yes No
Instantaneous full brightness? Yes No Yes
Dimmable? Some Some Some
Durable? No No Yes  


COSTS

LED bulbs are more expensive to buy than CFLs and CFLs are more expensive to buy than incandescents.  However, one should not be put off by the LEDs’ and CFLs’ relatively high prices.  Because they last longer you’ll have to replace them much less frequently than incandescents.  Also their power costs will always be much lower.   So what’s the bottom line here?  Will LED’s and CFL’s lower power costs and longer lives more than compensate for their higher initial costs?  Present worth analyses provide a way to determine total costs over a period of time in today’s dollars, giving us a way to make rational cost decisions.   The alternative with the lowest present worth is the one that’s least expensive when all is considered.

Table 3 presents a cost analysis of some representative 800-lumen bulbs.  Calculations assumed a study period of 17.1 years (equal to the life of one LED bulb), a current electrical cost of 20 cents per kilowatt-hour (in the San Francisco Bay area), an electricity inflation rate of 1.3% /year, a bulb inflation rate of 8% /year, and a discount rate (the interest rate a customer can get at a bank) of 1%.

Table 3.  Costs
         
  Incan-    
Parameter descent CFL LED Comment
Manufacturer Satco GE Feit
Model S4166  Reveal A21
Lumens 800 800 800
Watts 60 13 9.5
Advertised life, years 0.8 6.8 17.1 Assumed use 4 hrs/day
Number of bulb replacements 25 4 1
Current bulb costs, $ 1.00 9.29 24.99
Present worth, $ 353 113 81
     Of bulbs (A) 49 47 25
     Of power (B) 304 66 48
     Total cost (A + B) 353 113 73  


The LED alternative is the least- cost alternative, with CFLs trailing and incandescents far behind.  Replacing your 800-lumen incandescent with a LED bulb will save you $353 – 73 = $280 over the lifetime of your LED bulb.

CARBON DIOXIDE EMISSIONS

The amount of CO2 emitted at the power station while powering a light bulb is the product of the bulb’s power draw and the amount of CO2 generated while producing that power.    Using a California-wide ratio of 0.52 lbs CO2 per kilowatt-hour (kwh) of power generated, 136 pounds of CO2 are created while powering an 800-lumen, 9.5- watt  LED bulb over it’s lifetime.  During the same time 780 pounds of CO2 are created while powering period an 800-lumen, 60-watt incandescent bulb.   The disparity is wider in states where  a higher the ratio of CO2/ kwh  prevails, for example, in states relying on coal as a primary power source.  

SUMMARY AND RECOMMENDATIONS

This analysis suggests that CFLs and LEDs are superior to incandescents in virtually all aspects.  CFLs lag LEDs in electric efficiency, reliability, overall cost, and durability and must be handled as hazardous wastes when exhausted.  LEDs’ edge seems likely to increase in the future as their costs will probably drop as their market matures.   For these reasons, I recommend LEDs.  Bulb costs vary widely, even within the same category (LEDs for example), so shop around.  Also make sure that the bulb you buy fits in to your lighting design and is compatible with your light fixture and light covering.  Finally, some LEDs are not designed to be mounted bulb down, as they would be if ceiling mounted.  Mounting an LED bulb down may reduce bulb life significantly.


Doug Merrill


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