Solid-state lighting (SSL) refers to a type of lighting making use of light-emitting diodes (LEDs) as sources of illumination instead of electrical filaments or gas. LEDs overcome a number of the disadvantages of traditional lighting owing to their significantly longer lifetime, superior spectral output with good color rendering ability, higher efficiency, and lower energy consumption. These attributes make them desirable for many lighting applications that had been previously the realm of incandescent or fluorescent lights. Nonetheless, LED's have some disadvantages as well, including the highly temperature-sensitive nature in both performance and reliability, poor light coupling through the LED surface which decreases external quantum efficiency, a highly directional external intensity distribution which ends up with light pollution. A number of design challenges and costs are associated with switching traditional lamps with LED lights. These design challenges include light production, thermal management, and manufacturing cost control.
For most applications it is hard for the user of the LEDs to set a tight specification on flux and color; generally a range of a color is used. Challenges lie in the matter that LEDs, when manufactured, are produced in a distribution of colors (wavelengths or color corrected temperatures, CCT), light output (intensity or luminous flux), and forward voltage/efficacy (Vf or lumens per Watt). Generating a matching color and light output in multiple fixtures is extremely important; it is critical both in the occasion of fixed or permanent installations. Color variations in LED arrays are a fundamental design consideration, particularly for applications such as wall washing, where disparities in adjacent LEDs can create unexpected color effects on the target surface.
LED performance predominantly relies on the ambient temperature of the operating environment. This criticality is especially noticeable in high power LED applications. In spite of the remarkable improvement in energy efficiency over currently established light sources, light sources employing light emitting diodes (LEDs) still convert between 20 to 50% of the power they are fed into heat. Heat can often lead to permanently damages to the LED, degrades LED performance by causing reduced light output, and ends up in a premature device failure. As a result, adequate heat-sinking or cooling is essential to maintain a long lifetime for the LED, which is extremely important in applications where the LED must operate over a broad range of temperatures.
LEDs unlike conventional light sources for example incandescent bulbs cannot effectively cool themselves. For this reason additional heatsinking or cooling means are needed to prevent overheating. While high thermal conductivity materials are often used to propagate the heat out over a substantial area, these high thermal conductivity materials come with the addition of significant weight and cost. This raises the cost of not only the light sources as a result of shipping costs and materials costs but also the fixtures which use those light sources. Additionally, for driving an illumination system, the LED driver is commonly designed as general-purpose circuitry for use with a wide selection of LEDs. This further increases the overall cost. Aside from that, white light LED costs are changing, pushing designers to use caution in specifying LEDs for specific lighting applications.
Glare and spill light, and halo effect light, are known as as light pollution. By the very nature of their design and operation, LEDs produce a directional light output. LEDs are small, concentrated sources of directional light, and may often times create glare when used for general illumination. In particular, glare and spill light are well-known and truly serious concerns for high intensity wide area lighting. Glare occurs in these applications as a consequence of contrast of the brightness of the light from the lighting fixture high up in the sky against the darkness of the sky. The glare could be very annoying and discomforting.
Flicker and other visual anomalies sometimes appears when there are sufficiently large ripples in the DC current offered to the SSL. Flicker in electrical lighting is often brought on by the temporal variation in the power supply to the light source. Flickering in LED lamps can occur mainly because these devices are typically driven by LED drivers having regulated power supplies which provide regulated current and voltage to the LED lamps from AC power lines. The LED emits light by being supplied with power through a predetermined power supply unit. When power supplied by the power supply unit is unstable, the light emitted from the LED may flicker as a sign of a malfunction. That is, a flicker of the LED happens when a current waveform of the power supplied to the LED is imbalanced.