| The Economics of Dimming

Technical white paper
Dr. Ian Rowbottom
May 26, 2010

 

Executive Summary: Using assumptions outlined in the text—

A residential dimmer can save $9 (or more) in electricity and bulb replacement costs per year, and can pay for itself in about two years. A commercial dimmer can save $85 (or more) in electricity costs per year, and pay for itself in about one year. Higher dimming use will result in shorter payback periods.

Residential Dimming

The typical investment for a Lutron residential single-location 600 watt dimmer ranges from $9.97 for rotary dimmers to $29 for Maestro® dimmers, with the average retail price being $16. This investment can be easily recouped by substantial energy and bulb replacement savings that result from using the dimmer. Here’s how:

1. Lighting electricity usage for a typical residential space that can use a dimmer = 294 kWh/year i

2. Average energy savings while dimmer is in use = 20% ii

3. Total electricity savings = decrease in energy consumption (294 kWh/year x 20%) = 59 kWh/year

4. Average cost of residential electricity = $0.1155 per kWh (2009 average) iii

5. Average annual cost savings = 59 kWh/year x $0.1155/kWh = $6.81/yr

Dimming not only saves electricity, but also extends lamp life. At a dimming level of 20%, using a typical 60W light bulb, the bulb life extension will be 4 times iv. A typical incandescent light bulb is rated for 750 hours.

We can now calculate how many light bulbs we would use at full compared to how many would be used if dimmed by 20%:

Energy consumed per bulb to end of life = rated life x rated power x running power factor x bulb life extension factor

Non-dim consumed energy per bulb to end of life = 750 x 60 x 1 x 1 = 45 kWh

Dimmed consumed energy per bulb to end of life = 750 x 60 x .8 x 4 = 144 kWh

Thus, the bulbs run much longer before failure in the dimmed case. Therefore, we would require 6.5 bulbs (294/45) at full power to consume the 294 kWh/year compared to 1.63 bulbs [(294/59) / 144] for the 20% dimmed case. At a typical cost of $0.50 per bulb, the dimmed application would save $2.43 [(6.5 – 1.63) x .50] in bulb costs compared to the non-dimmed case.

We estimate a Lutron residential dimmer saves $9.24 ($6.22 + $2.43) per year in electricity and bulb savings.

An average residential dimmer (at $16) pays for itself in less than 2 years. A rotary dimmer (at $9.97) pays for itself in approximately 1 year.

 

Energy savings over the life of the dimmer

A Lutron dimmer is designed to operate for at least 10 years, meaning that each dimmer will ultimately pay for itself several times over.

1. Minimum design life of dimmer = 10 years

2. Minimum lifetime cost savings = 10 years x $9.24/year = $92.40

3. Net savings = $92.40 – $16 = $76.40 per dimmer

 

The more you dim, the more you save

Dimmers operated for longer periods of time, at higher wattages, at dimming levels greater than 20%, save even more electricity and money. For example, here’s what happens when you dim a light by 50% for 5 hours/day and assuming a 300W load:

1. Annual electricity savings = decrease in load (300 W x 50%) x hours used (5 hrs/day x 365 days) = 273.8 kWh/year

2. Annual cost savings = 273.8 kWh/yr x $0.1155/kWh = $31.62/year

In this case, a single residential dimmer saves $31.62 per year in electricity costs. This would reduce this payback period for an average dimmer (at $16) to about six months.

 

Commercial Dimming

The typical investment for a Lutron commercial dimmer is $100. This investment is a little higher than the residential purchase because the dimmer is required to control larger loads. However, the running hours are much longer in a commercial installation and this results in larger savings. Here’s how:

1. Average commercial dimmer load = 1200 W vii

2. Average energy savings while dimmer is in use = 20%ii

3. Average daily commercial dimmer use = 14 hours/day ii

4. Average number of days used for commercial operations = (50 weeks x 5 days) = 250 days

5. Average annual electricity savings = decrease in load (1200W x 20%) x annual use (14 hours/day x 250 days) = 840 kWh/yr

6. Average cost of commercial electricity = $0.102/kWh (2009 average) iii

7. Average annual cost savings = 840 kWh/yr x $0.102/kWh = $85.68/yr

A single Lutron commercial dimmer saves an average of $85.68 per year. An average commercial dimmer (at $100) pays for itself in about 1 year and 2 months.

 

Energy savings over the life of the dimmer

A Lutron commercial dimmer is designed to operate for at least 10 years, meaning that each dimmer will ultimately pay for itself several times over.

1. Minimum design life of dimmer = 10 years

2. Minimum lifetime cost savings = 10 yrs x $85.68/year = $856.80

3. Net savings = $856.80 – $100 = $756.80 per dimmer

 

Conclusions

Residential dimming

1. We estimate, a residential dimmer can save $9.24/yr in electricity and bulb replacement costs compared to a switch.

2. An average residential dimmer pays for itself in less than 2 years. After that, the customer continues to save $9.24/year, every year.

3. If the dimming level is increased, the savings will be larger and the payback period will be shorter.

Commercial dimming

1. A commercial dimmer can save $85.68 per year in electricity costs compared to a switch.

2. An average commercial dimmer pays for itself in 1 year and 2 months. After that, the customer continues to save $85.68 per year, every year.

3. If the dimming level is increased, the savings will be larger and the payback will be shorter.

 

Endnotes

  1. US Department of Energy Lighting Market Characterization Study, Navigant Consulting, Sep 2002.
  2. California Energy Study http://www.energy.ca.gov/efficiency/lighting/VOLUME01.PDF
  3. Energy Information Administration http://www.eia.doe.gov/cneaf/electricity/epm/table5_3.html
  4. IESNA handbook, 2000, p.6-13
  5. GE lighting http://genet.gelighting.com/LightProducts/Dispatcher?REQUEST=RESULTPAGE&CHANNEL=Consumer&BREADCRUMP=General+Purpose_Standard%230
  6. Lowes http://www.lowes.com/ProductDisplay?partNumber=169088-3-10506&langId=-1&storeId=10151&productId=1207025&catalogId=10051&cmRelshp=sim&rel=nofollow
  7. Lutron survey of commercial lighting designers, architects and field service engineers

Telephone: 610.282.3800

International: +1 610.282.3800

World Headquarters

Lutron Electronics Co., Inc.

7200 Suter Road

Coopersburg, PA 18036-1299

USA

www.lutron.com

©2010 Lutron Electronics Co. Inc.

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