Exterior lights illuminate grounds and open areas. The key factors to consider are the type of lights, the brightness and range the lighting system can deliver, and the attractiveness or elegance of the system. Most exterior lighting systems now feature LEDs, owing to their low power consumption and long life. The brightness of the light depends on the bulb. Bulbs for external lighting systems normally range from 85 lumens to as high as 4500 lumens, depending on the application and the extent of the coverage area. Floodlights are heavy-duty and powerful external lighting systems, featuring a number of high-intensity LED lights and a powerful reflector. These lights have advanced features, such as the ability to deliver instant bright light, and often find use to illuminate tennis courts, stages and the exterior of buildings. Many external lighting systems now have sensors to detect movement and brightness of natural light, to turn on and off automatically. Many external lighting systems are equipped with solar panels and run on solar power. A useful accessory to go with external lights is a socket earth pole, which offers effective grounding. The best external lighting systems are durable enough to withstand the weather and elements. Common materials for lighting systems include coated aluminium and impact-resistant plastic.