Guest post by Jim Brodrick, U.S. Department of Energy
Some of you may have seen a new report on street lighting by the Lighting Research Center (LRC) at Rensselaer Polytechnic Institute. A number of people have asked for my comments on that report, so here goes.
In a nutshell, the LRC report implies that GATEWAY reports are potentially misleading, and describes an in-house study – conducted by the LRC’s National Lighting Product Information Program (NLPIP) – that found LED street lighting to be vastly inferior to high-pressure sodium (HPS) and pulse-start metal halide (PSMH) fixtures for collector roads (roads that connect local streets with arterials). A corollary implication of comments LRC published in association with the report is that DOE is biased in favor of SSL at the expense of other lighting technologies, and is blindly pushing it without regard to its suitability.
As I’ve mentioned before, GATEWAY focuses on LED products for a very good reason: GATEWAY is part of DOE’s solid-state lighting program, and DOE was specifically directed by Congress to support the development, improvement, and deployment of SSL technology. Why? Because no other existing lighting technology has as much potential to save energy and improve lighting service over the next 20 years. But that doesn’t mean DOE has tunnel vision when it comes to solid-state lighting. On the contrary, DOE has other programs that promote efficient conventional lighting technologies, such as the Commercial Lighting Solutions program and the Commercial Building Energy Alliances.
And just as important, as anyone who reads these Postings knows, DOE’s solid-state lighting program regularly publishes materials critical of a wide range of LED products on the market and urging caution in product selection. See, for example, the CALiPER testing summaries, numerous presentations urging potential buyers of LED products to be very careful in product selection, and most recently, Municipal Solid-State Street Lighting Consortium guidance which states that “the surest way to reduce risk, while simplifying the process of luminaire selection and lighting design, is to enlist the help of a qualified lighting professional.” That doesn’t sound like DOE urging a headlong rush into LED products.
The purpose of GATEWAY is to document real-world experience with LED lighting products in the field. This is critical because even with well-designed products, many problems and performance issues are not apparent until the products are installed. GATEWAY installations will also yield important information over time about lumen maintenance, reliability, maintenance costs, and energy savings. As a new technology, SSL lacks this long-term track record. Conventional lighting technologies already have a track record, and thus are less in need of an intensive government effort to document their performance.
What’s more, GATEWAY was created to evaluate LED products based on the parameters of the host site, and an extensive pre-investigation is always conducted before the actual demonstration begins, in order to determine the feasibility of using SSL. If DOE determines that conventional technology products are clearly more suitable for the application, then no GATEWAY demonstration takes place at that site – we advise the owner that we don’t think LED products are a good investment for the site at this time, and move on.
As for the LRC study, a critical error was committed at the outset which affects all of its conclusions. Although I’m sure it wasn’t intentional, LRC selected some woefully underpowered LED products to compare with HPS street lamps, and then concluded that LED products aren’t competitive because of the high cost of having to purchase additional luminaires and poles to make up for the insufficient light. That’s kind of like racing a Ford Pinto against a Chevy Corvette and then concluding that all Chevys are faster than all Fords.
There are plenty of higher-powered LED products on the market that are appropriate for the study application, and selecting them would have resulted in higher luminaire output, thereby providing a fair comparison with the HPS products that were selected. This fundamental flaw in methodology completely undermines the LRC’s general statements about LED performance. The conclusions that LED systems need more luminaires and poles, and therefore have significantly higher first costs, are a direct result of this critical error in product selection, and consequently are baseless.
The LRC published several other reasons for why they think GATEWAY reports are misleading, but these don’t hold water either. For example, the LRC criticizes GATEWAY for basing our economic analyses on existing pole spacing, but changing pole spacing at test sites would often be exorbitantly expensive, not to mention disruptive to the site’s business. And LRC criticizes GATEWAY for a study in which illumination levels were cut in half by the new SSL luminaires, accusing GATEWAY of attributing the resulting energy savings to SSL – when in fact the report for that GATEWAY study contains a very clear caveat urging readers not to attribute the energy savings to the new technology, and makes clear in its conclusions that the energy savings were due to reducing illumination levels at an over-lit location.
In general, the LRC’s comments on DOE’s GATEWAY program underscore the difficulty of comparing the economic and energy performance of systems in the field, where – unlike laboratory or computer simulations – all other factors can’t be held constant. That’s precisely why we’re so careful not to draw generalized conclusions based on each GATEWAY report, and why each report always plainly states that the economics and energy performance it contains are based only on that particular site and the particular products analyzed.
In fact, as most of you know, the importance of doing due diligence on specific products, including confirming that those products are suitable for the application in question, is emphasized by DOE throughout its SSL presentations and published materials. LRC’s approach of simply taking products selected by distributors “as is,” without independently confirming that the selected models were actually suitable for their simulated test site, serves as an excellent illustration of the incorrect conclusions that can result from trying to apply unsuitable luminaires to a site.
Although the LRC’s intentions were good, the results of their study are seriously flawed. Street lighting is one of the applications for which SSL clearly is already competitive with incumbent technologies, as GATEWAY has shown and numerous members of DOE’s Municipal Solid-State Street Lighting Consortium – who have investigated LED products on their own – will attest. That doesn’t mean every LED street lighting product is a good one, or that SSL is the right choice in every street lighting application. But it does mean that SSL should be in the running for street-lighting applications when saving energy and money are important considerations.
