Thursday, January 9, 2014

Payback In Replacement of T8 Fluorescent Lamps, With LED Tubes

Consider a 4-foot T8 fluorescent  drawing 32 watts, 2800 lumens output, 360° beam angle, estimating downward display of 50% of light, with some reflection. Its replacement LED tube draws 16 watts, with display of 1500 lumens over a 140° beam angle. For equal task light intensity, the power draw is reduced from 32*1500/1400 watts, or 34 watts, to 16 watts. Say the fluorescent tube costs  $5 and lasts 25,000 hours. The T8 LED costs $30, and lasts 50,000 hours. What is the simple payback time of the more-costly LED if lights are operated 12 hours per day, and how much does the LED save over 50,000 hours? Consider electricity at 11 cents per KWH.

Savings per year are ((34-16 watts) * $0.11 /1000 watt) * 365 * 12 hours/ year = $8.70 per year.

Payback is annual electricity savings, against difference in cost of expended tubes, $30 - 2*$5 = $20.

Payback Period = $20 /$8.70 per year = 2.3 years. The payback period is inversely proportional to hours per year usage. At four hours per day over your kitchen, multiply by three, and find seven year payback OK too.

Over 50,000 hours, save electricity cost difference ((34 -16 watts) * $0.11 /1000 watt) * 50,000 = $99. Expect more, with doubled real life of the LED light, and sure-to-rise cost of electricity.

This is good-enough payback, and maybe light quality is better. Link here to LED components by ATG Electronics:

Here is a photo showing two of these tubes. Each ships with pin protectors and a power supply converting 90 - 305 VAC to 22 - 36 VDC, maximum 25 watts. Each 16 watt tube needs its own converter.

Now search the title of this post . With similar math, Cree finds similar two-year payback in commercial 12-hr per day usage.

What then, are the negatives in this? Find here a review by Nevin Lock, a consultant to Bonneville Power Administration: 

Those who get involved may avoid trouble by using kits. I bought a dozen of the ATG four-foot tubes not as troffer kit, accepting 6000°K , for relamp of a commercial sign box. I have been recruited in this by ATG, to be an unbiased commenter. We are all wary, and things are happening slowly. I returned the ATG tubes in 2014, with prejudice. 

How shall we react to continued sale of LED tubes as simple re-lamp, for example as offered by Costco , Fall 2016?

$44.99, with free shipping.
Feit 4 FT LED Replacement Tubes, 4-pack
Uses 17W
1700 Lumens
4100K Cool White

Life Hours 50,000 Hours



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David Stevens said...

There are some additional energy dollar savings to be gained in commercial buildings.

All energy eventually becomes heat energy. If you cut the energy used by lighting by 50% that also reduces the building's heating load on the air conditioning. In colder weather it will also increase the energy needed for heating but the balance of the energy dollars saved on cooling and spent on heating will almost always increase the savings over what is saved for lighting alone.