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Back to Saving Maui's Starry Night Skies

Retrofitting Maui's Street Lights
with Fully Shielded Luminaires

Prepared by Lee Altenberg, Ph.D.

Presented to the Subdivision Standards Committee, Maui County, January 8, 1999

Summary: The night-glow caused by uplight from street lights could be eliminated, and the night skies of Maui returned to their pristine beauty, by retrofitting the current stock of street lights with fully shielded luminaires. By retrofitting the luminaires when the bulbs fail, the entire stock of street lights could be retrofit in about two years, at a cost that would be recovered within about three years of installation by electricity savings on the more efficient luminaires.

Maui's night skies are already seriously degraded by light pollution from the street lights that have accompanied the rapid development of the island over the past 20 years. Other major sources of light pollution include the outdoor sports fields. As a consequence of the "night-glow" from these light sources, the towns of Kahului and Kihei in particular have lost the beauty of Maui's breathtaking starry nights, and other sites of development are not far behind. Not only does this detract from the pleasure of living here, but because Maui's beauty is the reason millions of visitors come here, light pollution is corrosive to Maui's economic base.

The growth of light pollution on Maui is a combined product of:

  1. the subdivision and development of agricultural land,
  2. the lighting requirements for new developments, and
  3. the design of street lights.

Because the first two items have many issues attached to them, I will defer on these subjects, and here focus on the third item, the design of street lights, which has a clear technical solution: full shielding.

Over the past 5 years, a growing number of communities and States around the country are now prohibiting the installation of the "cobra head" street light with the "fish bowl" luminaire, because through their faulty design, they cast about 30% of their light sideways and up in the sky ("uplight"). With a simple design change, street lights can be made to shine all their light downward toward their target areas. These designs are called "full-cutoff" or "fully shielded".

These fully-shielded luminaires cost no more than the fish-bowl luminaires, and are manufactured by numerous companies. They allow a reduction in the wattage of the bulbs by 30%, since this light is no longer wasted on lighting up the sky. Hence there is no reason why the County Code should not be immediately modified so that all future street light installations use fully shielded luminaires.

The question remains, however, what to do with the installed base of street lights that are creating Maui's current night-glow. I researched the cost of retrofitting Maui's stock of street lights with fully shielded luminaires.

Based on the data I was given, it should be possible within two years to retrofit 85% of Maui's street lights, at a cost which would be recovered through electricity savings within about 3 years of retrofitting. This schedule is based on retrofitting each street light when its bulb needs to be replaced. An accelerated schedule could also be adopted that would retrofit all of the island's street lights within a year, at a cost that would be recovered by electricity savings within 5 years.

These results were calculated as follows, using the data given in the table below. There are approximately 3,000 to 4,000 street lights on Maui. The cost of a new luminaire is about $150. The cost of labor to exchange a luminaire or replace a bulb is about $100 (depending on the travel costs to the site). However, the cost of additional labor needed to exchange a luminaire when already exchanging a bulb is negligible. So the cost of retrofitting the luminaires at the time when the bulbs burn out is 4,000 X $150 = $600,000. The cost of an accelerated retrofit program is 4,000 X ($150 + $100) = $1,000,000.

Because fully shielded luminaires cast all their light on their target, and none into the sky, they can provide the same illumination with only 70% of the electricity use as the "fish bowl" luminaire. Hence, a 250 W bulb on a fish-bowl street light can be replaced with a 150 W bulb, and a 150 W bulb can be replaced with a 100 W bulb. This reduction in wattage will produce the following operational savings:
Wattage Reduction: Calculation: Savings per year: Years to recover cost:
From 250 W to 150 W: (100 W reduction per street light) * (4,000 street lights) * (10 hours/day) * (365 days/year) * $0.145/KWH [Note: $0.162/KWH as of Feb. 2000] = $211,700/year 2.8 years
From 150 W to 100 W: (50 W reduction per street light) * (4,000 street lights) * (10 hours/day) * (365 days/year) * $0.145/KWH [Note: $0.162/KWH as of Feb. 2000] = $105,850/year 5.7 years

I could not get a figure on the relative numbers of 250 W, 150 W, and 100 W lights installed. So the cost recovery time would be somewhere between 2.8 and 5.7 years based on these estimates. On the accelerated retrofitting schedule, the cost recovery time would be between 4.7 and 9.4 years. These cost-recovery time estimates do not depend on the total number of street lights, but only on the wattage reduction.

Since the data used in these calculations were off-the-cuff estimates given me by Mike Sylva of MECO, they leave room for variation in the final cost-recovery times estimates. There may be ways to reduce costs, not considered here. And after the costs of the retrofitting program have been recovered, the lower power usage of the new lights will continue to generate revenue savings for County indefinitely. Should electricity rates increase in the future, the cost-recovery time would be even shorter.

An additional benefit from the retrofitting program is that it will lessen the load on MECO's power generation capability between 0.150 and 0.4 megawatts (3,000 X 50 W = 0.150 MW; 4,000 X 100 W = 0.4 MW), depending on the current street light wattage usage. This would contribute to the demand-side-management strategy being consider in order to forestall the need to build additional power generating capacity on the island.


The economics of retrofitting Maui's street lights to make them fully shielded would appear to allow the entire stock of existing lights to be retrofitted within a couple of years, with net cost savings to the County after three to five years. The effect on the island would be spectacular: Maui's breathtaking starry night skies would be visible again from every neighborhood on the island; the increasingly urban-looking night appearance of Kahului, Wailuku, and Kihei as seen from Upcountry would be replaced with soft and muffled views of the towns. The growing band of lights on the side of Haleakala would be replaced with the stark silhouette of the mountain against the sky. The restoration of these aspects of Maui's beauty would be of benefit to residents and visitors alike.

Table of data on Maui street lights
Item: Data: Source:
Cost of street light luminaire: ~ $150 Mike Sylva, MECO, 871-2394
Labor cost to replace luminaire: ~ $100 Mike Sylva, MECO, 871-2394
Marginal labor cost to replace luminaire when replacing bulb: ~ $0 Mike Sylva, MECO, 871-2394
Wattages used: 100 W, 150 W, 250 W Mike Sylva, MECO, 871-2394
MECO electricity rates ~ $0.145 / KWH [Note: $0.162/KWH as of Feb. 2000] MECO monthly bill
Number of street lights on Maui: 3,000-4,000 Mike Sylva, MECO, 871-2394
Lifetime of street light bulb ~ 1 year Mike Sylva, MECO, 871-2394
Power savings using fully shielded luminaire: ~ 30% International Dark Sky Association


I have collected information on the nationwide efforts to bring back the night skies, and include it with this report. Included are lighting ordinances from

I have also included information on vendors of fully-shielded light fixtures. It is even possible to shield the lighting at sports fields so that they do not contribute to urban night-glow. Information on a vendor of shielded sports-lighting is included. Also included is technical information on the issue of light pollution.