Sustainable lighting using luminescent material May 2019

Traditionally, lighting brightness and lighting uniformity for road surfaces at the tunnel threshold, exit, transitions and interior zones are the key criteria for road tunnel lighting standards. Research shows that the operational design of road tunnel lighting should not only focus on brightness and uniformity of the road, but also on minimizing the black hole phenomenon at the tunnel entrance and the white light phenomenon at the tunnel exit.

LUMA application increases illumination in the tunnel on the right as compared to ordinary coating and ceramic tiles on the left

LUMA, a new coating product developed at the An Hui Zhongyi New Material Science and Technology institute in Hefei, China, features a non-flammable, anti-mildew, anti-corrosion, anti-pollution, self-cleaning, negative oxygen ion releasing finish that alleviates contamination to tunnel walls from car exhausts, increases in-tunnel visibility and air quality, and provides illumination for evacuations.

LUMA has been used in road tunnels in China and was recommended for application in the national traffic system. It has been applied on tunnel surfaces, road markings and tunnel signage fixtures. It simultaneously fulfils safety, comfort, environmental, and energy efficiency requirements for tunnel lighting.

Science of the product

Any light source has invisible electromagnetic waves with wavelengths of between 200nm and 380nm. When an electromagnetic wave within this range radiates to the rare earth aluminates (or silicates) containing Eu2+ and Dy3+ in LUMA, it will excite the outer layer electrons of the rare earth ions to transition between 4f or 5d to 4f layers, thus generating a broadband charge migration resulting in illumination.

Entrance black hole phenomenon

Exit white light phenomenon

Black hole eliminated with LUMA

White hole eliminated with LUMA

When the light source vanishes, the electrons in the outer layer of the atomic nucleus of the rare earth ions return to their original status, where the wavelength of light produced is between 480nm to 580nm, resulting in delayed luminescence with an afterglow longer than 12 hours.

In a lighting environment, the comfort of the human eye is determined by the relationship between colour temperature and lighting brightness. When the main peak wavelength of illuminating light falls in the range of 490nm to 570nm, the visibility of small objects to the human eye increases significantly, which in turn helps mitigate visual fatigue.

In addition, the insulating mica powder and nano-scale stone in the LUMA product absorbs electric charges and ionizes and catalyses the oxygen and water molecules in the air, continuously producing negative oxygen ions. Wall surfaces that release negative oxygen ions oxidize surface pollution and can be easily cleaned.

Technical achievements

LUMA breaks through the limitations of conventional lighting techniques by addressing five key considerations for tunnel lighting:

• Minimise the brightness differential between the inside and outside of the tunnel.
• Increase the light wavelengths to improve the visible distance of small objects.
• Provide correct lighting at tunnel entrances and exits, as well as inside tunnels, to eliminate visual fatigue and reduce visual error.
• Guarantee a stopping sight distance in front of headlights to increase the visibility of obstacles.
• Ensure escape signs are visible to the human eye even in the event of smoke filling the tunnel.

Organic silicon coating on the left compared to LUMA coating on the right

LUMA achieves these objectives by offering:

• A brightness increase of 30% to 160% for various lighting facilities and natural light
• Delayed luminescence (≥12 hours)
• Resistance to acids, alkali and water (≥720 hours)
• Ageing resistance to artificial climate (≥3,000 hours)
• Stain resistance (≤10%)
• Release of oxygen ions (≥350 ions/cm³)
• With afterglow, visibility ≥2m when smoke concentration is 30,000mg/m²

Benefits of LUMA

Increasing the wavelength of illuminating light in the tunnel environment to 490nm to 570nm not only makes the human eye more comfortable, it also improves the ability of the eye to see small objects and to see through smoke. LUMA lessens the effect of visual fatigue and reduces visual errors, while providing emergency escape lighting in the event of an in-tunnel accident or disaster.

It is estimated that LUMA has saved 22 million RMB (US$3.25 million) in tunnel lighting energy costs since its introduction in 2016. As the total length of established road tunnels in China exceeds 15,000km, if all Chinese highway systems used LUMA, more than ten billion RMB (US$1.5 billion) could be saved each year on lighting.

Comparison of a tunnel using LUMA coating (left) and ordinary coating (right)

With the application of LUMA, short highway tunnels do not have to be equipped with lighting fixtures. For medium, long or extra-long tunnels, lighting fixture configurations can be reduced by 25%. In mountain tunnels, lighting fixtures may not have to be activated during normal operation and can rely safely on vehicle headlights and reflections only.

The LUMA product significantly reduces the energy consumption for tunnel lighting and effectively reduces the operational and maintenance costs of road tunnels. It alleviates contamination to tunnel walls from car exhaust, increases visibility and air quality within the tunnel, and provides illumination for escaping from accidents. In 2018, LUMA received the Technical Innovation Product of the Year Award of the International Tunnelling and Underground Space Association.