Comparison of Edison screw bulbs

Despite having a simple design of few unique materials, and desirable electrical properties, there is a push to replace incandescent bulbs. However, the replacement needs to be convenient for consumers, where replacement of the fixture is impractical. Most lights in homes have an Edison screw base. Compact florescent lights (CFLs) made a real attempt, but some of the benefits of CFLs are hype. There are issues with manufacturing complexity, power factor, disposal complexity, etc. (A nice life-cycle analysis of incandescent and CFL was written by Laurie Ramroth entitled “Comparison of Life-Cycle Analyses of Compact Fluorescent and Incandescent Lamps Based on Rated Life of Compact Fluorescent Lamp.”)

A more recent alternative is light emitting diodes (LEDs). They are still more expensive than CFLs but their prices are being more practical, and they have some benefits that are appealing such as very long life, which is great for hard to replace bulbs.

Here I simply want to share a few thermographs of a typical replacement. Two 25W incandescent bulbs were replaced with 3W LED bulbs in a location where the bulbs on for several hours of the day, a stairway with a light switch only at the top of the stairs.

Thermograph of incandescent in fixture

Thermograph of LED in fixture

Thermograph of 3W LED bulb

Thermograph of 13W florescent bulb

Thermograph of 25W incandescent bulb

Thermograph of 25W incandescent bulb, showing filament

Incandescent 25W purchase price = $5.05 (pair) $2.53 (each)

LED purchase cost = $10.99 (pair) $5.50 (each)

Electricity cost = $0.11 / KWHr

Incandescent cost for X Hr = 2.53 + 25 X / 1000 * 0.11

LED cost for X Hr = 5.05 + 3 X / 1000 * 0.11

LED break even in X Hr where [Incandescent cost for X Hr] = [LED cost for X Hr]

LED break even in 1041 Hr.

Incandescent cost for 50,000 Hr = 2.53 (50000 / 2500) + 25 X / 1000 * 0.11
= $50.60 + $137.50 = $188.1

LED cost for 50,000 Hr = 5.05 + 3 X / 1000 * 0.11
= $5.05 + $16.50 = $21.55

$188.1 / $21.55 = 8.73

Estimate of cost of removing heat by AC
1 KWHr = 3412.1 BTU

AC may require between 0.33 BTU and 0.5 BTU of energy to remove 1 BTU of heat, depending efficiency.

1000 Hr * 25W / 1000 = 25KWHr = 85,302.5 BTU heat
85,302.5 BTU heat * 0.5 = 42,651.25 BTU of cooling energy
42,651.25 BTU of cooling energy = 12.5 KWHr
12.5 KWHr * $0.11/KW = $1.38

1000 Hr * 3W / 1000 = 3KWHr = 10,236.3 BTU heat
10,236.3 BTU heat * 0.5 = 5,118.15 BTU of cooling energy
5,118.15 BTU of cooling energy = 1.5 KWHr
1.5 KWHr * $0.11/KW = $0.17

$1.38 / $0.17 = 8.12

[Incandescent consumption] / [LED consumption] = 25 W / 3 W = 8.33

Incandescent annual cost =
25W 10 Hr 365 Day 1 KW $0.11
—- —– ——- —— —— = $10.04 / Yr
1 Hr 1 Day 1 Yr 1000W 1 KWHr

LED annual cost = $10.04 / 8.33 = $1.21 / Yr

LED purchase cost = $10.99 (pair) $5.50 (each)

LED annual savings = $10.04 – $1.21 = $8.83

LED break even time = $5.50 / $8.83 = 0.62 Yrs

0.62 Yr 365 Day 10 Hr
——- ——- —– = 2,263 Hr
1 Yr 1 Day

Which is near the 2500 Hr life rating of the incandescent bulb.

Incandescent 25W purchase price = $5.05 (pair) $2.53 (each)

137

160

Light Voltage Amp Watt VA Power Factor Thermister surface temp. (F)
Incandescent 118.7 0.19 22 23 0.96 207
LED 119.0 0.03 2 3 0.79
Florescent 119.0 0.18 13 21 0.59

Leave a Reply

Close Menu