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Incandescent, CFL and LED bulbs. The choice is getting easy.


The TSM 371 Residential Housing class analyzed the simple life cycle cost of 5 different bulb selections for a utility room (12' x 15') requiring 9,000 lumens of lighting. The bulb choices were: 8 incandescent 75W bulbs vs 12 CFL vs 3 different LED bulbs. Local pricing was used for this homework. LED bulb life was 11,000 hours, CFL life 6,000 hours and incandescent life...a dismal 750 hours. All technical info straight from manufacturers' spec sheets.

Long story short...LED are best choice now economically, if their color rendering index meets your needs. Below is my answer key:

Bulb Type/Watts per bulb

Life Span (hr)

Bulbs/packs required

(Nbulbs)

Purchase cost

Operating cost

Total Cost

Incandescent /75W

750

11,000/750 = 15

8 bulbs/room x 15 iterations = 120 bulbs

$3.44/4-pack or $3.44 x 30 = $103.20

$0.88 x 8 bulbs x 75W/bulb = $528

$631.20

CFL

/13W

6,000

11,000/6000 =2

12 bulbs/room x 2 iterations = 24 bulbs

$8.89/pack x 2 packs

= $17.78

$0.88 x 24 bulbs x 13 W/bulb = 137.28

$155.06

LED 1/

12W

11,000

11,000/11,000 = 1

9 bulbs/room

$2.57/bulb x 9 bulbs

= $23.13

$0.88 x9 bulbs x 12 W/bulb = $95.04

$118.17

LED 2/

9W

11,000

11,000/11,000 = 1

12 bulbs/room

$5.31/pack x 3 packs

= $15.93

$0.88 x 12 bulbs x 9 W/bulb = $95.04

$110.97

LED 3/

8.5W

11,000

11,000/11,000 = 1

12 bulbs/room

Same as previous: $15.93

$0.88 x 12 bulbs x 8.5W/bulb =$89.76

$105.69



Note this was for non-dimmable bulbs.
Actual problem statement here:

Develop a cost comparison for the following lighting situation. A utility room (12' x 15') needs a minimum of 50 lumens/ft2. Menards has the following options for purchase:
  • 4-pack of 75W incandescent bulbs (A19 style) for $3.44, rated at 750hr, 1200 lumens, soft white, 2850K);
  • 12-pack of "60W equivalent" CFL bulbs (E26 base) for $8.89, 13 W/bulb, rated at 6000hr, 800 lumen, soft white, 2700 Kelvin;
  • Sylvania 75W Equivalent General Purpose (Daylight, Soft White, or Bright White all available at same price and specifications) A19 LED light bulb for $2.57 each, 12W, 1100 lumens, 80CRI, rated at 11,000hr, 5000K;
  • Feit Electric 60W Equivalent General Purpose Soft White A19 LED Light Bulb, 9 W/bulb, 4-pack for $5.31, 800 lumen, rated at 11,000hr, 80CRI, 2700K; or
  • for same price a "daylight" bulb rated at 8.5W/bulb, 5000k and all other specifications and price same as the Feit Soft White bulbs.

Figure out how many of each type of bulb you need at a minimum and you cannot "split" packs, i.e. you have to buy in the pack quantity, so if you need 9 bulbs but it's a 4-pack you must buy 3 packs. Don't consider the fixture costs, which may vary a bit depending on number of bulbs used, only the bulb costs. Ignore sales tax too.

Run the cost analysis including purchase cost and electric cost, assuming $0.08 per kW-hr. For each of these 4 cases, explain the pros and cons, and identify which you prefer for a utility room and why.




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