LED Outdoor Lights Worse for Sky Glow

Humans are making the night sky brighter. A new study quantifies to what degree blue-rich LED sources exacerbate this problem.

We have discussed at some length the issues raised by artificial lighting at night (ALAN), and the indications that the light produced by LED sources may be worsening them. (See related posts below for some links.) Mostly we have looked at the human melatonin system, and to a lesser extent the corresponding systems in other forms of life, and how they react to the enhanced blue content of light from LED sources.

Figure 1. Spectral power distributions of six modeled light sources. (FLED is 3,000K LED light with blue wavelengths filtered out.)

Here is an in-depth look at another aspect of ALAN, with special attention to the way LED light sources affect the picture. Researchers at the Naval Observatory and Dark Sky Partners, in Arizona, have published peer-reviewed research on the impact of light-source spectral power distribution on sky glow (PDF here). The work appeared in the Journal of Quantitative Spectroscopy & Radiative Transfer, and is freely available online.

Figure 2. Ratio of overhead scotopic brightness levels compared to an LPS source.

Six light sources were considered. Spectral power distributions are shown in Figure 1. The researchers calculated the sky glow apparent to human photopic and scotopic vision at the zenith and near the horizon, at varying distances up to 300 km from a modeled light source. The calculation summed up scattering from atmospheric molecules and aerosols, taking into account the power spectrum of the source.

Figure 2 shows the essence of the results. The researchers sum it up this way:

When the light sources are matched for equal photopic output, scotopic visual sky glow from sources with increased short wavelength emission such as white LED and metal halide appears dramatically brighter. The higher CCT LED and metal halide sources produce 6–8x the scotopic luminance of low-pressure sodium (LPS), and 3x that from high-pressure sodium (HPS), when observed from nearby. At 300 km the ratios decrease due to the greater extinction of the bluer sources, but remain 3-4x that from LPS and 1.6-2.4x that from HPS.

One can quibble with the methodology, which is described in fair detail in the paper. In a discussion on LinkedIn's Innovations in Light group (note: group membership may be required to follow the link), some experts do quibble with various points. But the conclusion seems solid that as the world moves increasingly to the use of LED sources for outdoor lighting at night, most of it at 4,000K or higher, we will be losing easy access to the night sky.

The paper is C.B. Luginbuhl et al., Journal of Quantitative Spectroscopy & Radiative Transfer, 139 (2014) 21-26.

Related posts

• White Light Suppresses Melatonin — but How Much?


• Banishing the Night


• LEDs & Sleep

— Keith Dawson, Editor-in-Chief, All LED Lighting

Fairchild Announces Flyback LED Driver with Power Factor Correction

The consumer electronics market, and the LED driver market in particular, have been developing rapidly in recent years. These markets are demanding power supplies/drivers with lower power consumption in shrinking form factors, as well as ultra low cost. Furthermore, due to the ever-increasing requirement for improved power quality, the use of power factor correction (PFC) circuitry for these devices is almost mandatory. Today, among various circuits, Flyback is the most attractive topology for these applications because of its simplicity. It provides the isolation, start-up, and the various other protections with one single switch. When it operates in discontinuous-conduction mode, a unity power factor can be achieved as well by using a simple constant on-time control.

Traditionally, a constant current LED driver for LEDs is implemented using an isolated Flyback converter with an output current regulation circuit as shown in Figure 1. The actual LED current is measured using a sense resistor and then compared with a reference to generate error voltage. The error voltage is transferred to the primary side through an opto-coupler and used to control the duty cycle of the primary side switching device. Although this allows excellent LED current regulation, the output regulation circuitry requires an optocoupler, reference voltage, and sense resistor, which increases system cost and deteriorates overall efficiency.

Figure 1: Conventional Secondary Side Regulated LED Driver (photo courtesy of Fairchild)

Primary-side regulation (PSR) can be an optimal solution to minimize the cost for LED drivers. This technique precisely controls LED current in the secondary side with the information in the primary side of the driver only. This not only removes the output current sensing loss but also eliminates all secondary feedback circuitry. This facilitates a higher efficiency offline LED driver design without incurring tremendous costs. This technique also regulates the LED driver output voltage without secondary feedback circuitry, which acts as an open lamp over-voltage protection guaranteeing better reliability of the driver.

Figure 2: Primary Side Regulated LED Driver and its Typical Waveform (photo courtesy of Fairchild)

Figure 2 shows the simplified circuit diagram of a primary-side regulated Flyback converter as well as its typical operation waveform. The key of primary-side regulation is how to obtain output voltage and current information without directly sensing.

During the diode conduction time, the sum of the output voltage and the diode forward-voltage drop is reflected to the auxiliary winding side as (VO+VF)*Na/Ns. By sampling the winding voltage at the end of the diode conduction time, the output voltage information can be obtained. The output current (Io) can be estimated by using the peak drain current (Ipk) of the MOSFET and the discharging time (tDIS) of the inductor current because output current (Io) is same as the average of the diode current (ID) in steady state. The output current estimation identifies the peak value of the drain current with a peak-detection circuit and calculates the output current using the inductor discharging time and switching period (ts). This output information is compared with an internal precise reference to generate error voltage (VCOMI), which determines the duty cycle of the MOSFET. With Fairchild’s innovative TRUECURRENT® technique, the constant output current can be precisely controlled.

With detected output voltage and current information, the control can be accomplished by the conventional feedback compensation method. Generally, Discontinuous Conduction Mode (DCM) operation is preferred for primary-side regulation. It features with better output regulation as well as unity input Power Factor (PF).

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Toshiba Launches Ultra-Small Chip Scale Package White LEDs for Lighting Applications

Toshiba Corporation announced the launch of ultra-small chip scale package white LEDs for lighting applications that can reduce the mounting area by 90% compared to conventional 3.0 x 1.4 mm package products. [1] The new TL1WK series will start sample shipment from April.

The new products utilize gallium nitride-on-silicon (GaN-on-Si) process technology and a new process technology that fabricates the elements of a packaged LED on an 8-inch silicon wafer. The LEDs are the industry’s smallest in sub-watt class (1/4-1/2W) white LEDs[2], with a package size of just 0.65 x 0.65mm, but they achieve a luminous efficacy of 130lm/W[3] and superior heat dissipation. Using the new white LEDs makes it possible to achieve a narrow beam in small-size lighting equipments and can contribute to innovation in lighting design.

The new white LEDs will be showcased at “Light+Building”, a trade fair for lighting and architecture in Frankfurt, Germany from March 30 to April 4.

Abu Dhabi to build facilities for safe electric lamp disposal

Abu Dhabi will soon build facilities to ensure the safe disposal and recycling of all types of electric lamps. It is an important move as some types of electric lamps contain mercury that pollutes groundwater after being dumped in landfills. Tadweer, the Centre of Waste Management - Abu Dhabi, is working on the development of storage units and recycling facilities for electric lamps as part of the master plan for waste management in the emirate, a senior official told Gulf News.

LG Chem Exhibits World's Largest OLED Light Panels at Light + Building 2014

LG Chem is currently participating in the biannual Light + Building Exhibition held at Messe Frankfurt.

When LG Chem joined the previous exhibition in 2012, the company had displayed its 60lm/W OLED panels which are still the world’s most efficient mass-produced OLED panels.

This year, LG Chem has increased the lifetime of these panels up to 40,000 hours (LT70). LG Chem is also exhibiting the world’s largest OLED panels at 320x320mm. These panels are available as samples on request.

Back in 2012, LG Chem had introduced its thin-glass type (bendable) OLED Panels which are now available as mass produced products. This year’s Light + Building introduces the new Plastic film type OLED Panels which are truly flexible.

At LG Chem’s booth, there are several mock-ups of actual lighting applications designed and developed by LG Chem’s designers. These mock-ups are placed in real-life scenarios such as a resting area, an office area, or hospitality areas.

Lgiht + Building which is the world’s largest lighting exhibition is being held from March 30th to April 4th this year. LG Chem’s stand is located at Hall 6.2, Booth A8.

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Cartoon: Organic LEDs

You have heard of USDA Organic, yes? If OLEDs continue moving into mainstream lighting, soon we may have DOE Organic.

Another vision from the twisted mind of Barney Walker.

P.S. You can enjoy more of Barney's creations at ohmart.org.

The Advantages of Parking Lot Lighting

There are a number of advantages within parking lot lighting than you might have initially thought. These can come in the form of design, professionalism, and security. Just as installing lighting will have advantages in the safety of pedestrians, it can also include advances in design, professional status and attraction of a business. Have a look at the following pro’s of parking lot lighting, and why it is something you should consider.

Protecting Your Business

Installing parking lot lighting protects your business in terms of the security and safety of your business’s assets. If your business has an unlit parking lot, then it’s more likely to attract unwanted attention from thieves and burglars who are looking to stay out of sight before potentially performing a break in.

If a building becomes attractive to the wrong kind of audience, expensive computers and other equipment are at stake, and there is no guarantee, despite security systems, that robbery will not be attempted during the late hours of the night.

While it is advisable to install security systems or cameras alongside parking lot lighting to ensure the highest level of security and prevention of risks, parking lot lighting is a factor that will help towards lowering the risk of criminal activities.

Protecting Pedestrians

Installing lighting into a parking lot also improves the safety of on goers and pedestrians. While a dark parking lot can be a perfect lurking spot for criminals and thieves, a well lit up area creates a safer environment for passers-by and local pedestrians.

Parking lot lighting also creates a safer environment for employees who might be working late or leaving their car in the parking lot. It gets dark early in winter and fall, which means staff who might be walking to their car on their way home are far more likely to get robbed than if the area was completely illuminated.

It is also a safety precaution in terms of driving in the pitch black darkness, as pulling out of a parking space is a lot harder in this case. To prevent any unnecessary accidents, installing parking lot lighting can help.

Design

The instalments of lights in a parking lot can not only improve the safety and security of the area and your business’s assets, but it can also create a better sense of environment and design. Lighting will illuminate the parking lot as well as the building where the business is present, making it stand out and look more presentable.

Professionalism

Installing parking lot lighting gives the building and business a higher professional status, making it appear well kitted out and ready for any clients who might come to visit.

Business’s who don’t have parking lot lighting installed will appear less practical than those who do, and clients visiting for meetings will be safer if the area is lit.

Overall, parking lot lighting might seem like an extra mile to go, but in fact, the extra mile you go will heighten the level of safety, security, design and professionalism a business already possesses.

About the Author: Charlotte Bonita is a commercial lighting blogger with a focus on energy efficient solutions, creating positive environmental impact and green factors during her spare time. Bonita has worked as a sales coworker for several years at MMA Consultancy and has done extensive research in the commercial lighting sector. She enjoys writing and sharing her findings in the industry with others.

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