FINDING: Replacing existing incandescent lamps with LED lamps in existing luminaires may under certain conditions cause the LED to overheat. Examples include downlights adjacent to insulation or in enclosed luminaires. This is true also of the use of SSL in industrial applications having higher ambient temperatures. LED lamp heat management needs to be addressed for all such applications.
SSL products, similar to fluorescents and HID, contain electronic components and without appropriate design can produce poor power quality and exhibit, for example, high THD and low PFs. This is a similar set of issues encountered by early deployments of electronic and hybrid ballasts for compact fluorescents and linear fluorescents lamps. High THD can cause flickering and excess current on shared neutral conductors. Low PF results in line currents higher than necessary to supply the required power.
SSL drivers, similar to fluorescent electronic ballasts, can cause radio interference, which can be annoying, especially to residential users. SSL drivers are required by the Federal Communications Commission to adhere to similar protocols as electronic ballasts in order to avoid these problems.5 This includes the integral drivers in SSL lamps.
Related to power quality, issues such as dimmer range and reliability, maximum/minimum units required on a control, repetitive peak voltage, and in-rush current can cause significant problems if not properly addressed (see “Electric Power Quality” in Chapter 4).
As an SSL product ages, its output gradually declines. It does not simply go dark, but its lumen output declines over time. This could be a liability issue in some applications where a specific level of illumination is required. One promising option to address this is incorporating a driver that will increase the operating current as the LEDs age to keep the luminaire at its specified output.
If SSL is to compete successfully, then its lighting quality should be equal to or better than non-SSL luminaires (IES, 2011, p. 7.64; IALD, 2006). Lighting quality issues include quantity of light, lighting ambiance, glare reduction, and color rendering and consistency (ALA, IES, IALD, 2010).
When a user installs SSL, they expect that the light will be equivalent to (seem the same as) an incandescent of the specified equivalent wattage. The quantity of light (i.e., the luminous flux measured in lumens) is the easiest metric to use, because it is easily predicted and measured. SSL has been successful in producing a quantity of light similar to standard luminaires in the lower lighting level environments. High lighting levels are currently harder to achieve because of the amount of heat management required with the additional wattage. As SSL modules become more efficacious, higher lighting levels will be achievable that do not encounter these problems in operation.
Whether a scene is pleasant, spacious, intimate, or dramatic depends on the luminance balance within the scene (IES, 2011, p. 4.26) and how light is layered. For instance, spaciousness is implied when walls and ceilings are evenly lighted. Pleasant scenes may have non-uniform lighting with stronger accent lighting and peripheral wall emphasis (Flynn and Spencer, 1977; IES, 2011). SSLs based on LEDs perform well for surface grazing for walls and ceiling coves and for accent lighting. Applications of SSLs based on OLEDs include lighted surfaces in addition to luminaires.
Examples of installations having lighting layers include uniform ceiling brightness balanced with select wall washing and occasional accent lighting; personal work areas may have under-shelf lighting with adjustable task lighting. All of these layers should be separately controlled to provide the desired luminance balance. The light output of SSL products can be very directionally controlled and, thus, has unique advantages in providing layers of light, especially for surface ambient, accent, and task lighting.
Brightness and Glare
Because SSL lighting is uni-directional, it has the possibility of high brightness, giving luminaires the potential of producing glare if not controlled properly. Luminaires can limit brightness through optical systems either at the module level or within the reflector and lens design. Methods include the use of remote phosphor modules or diffusing lenses or by indirectly lighting via reflectors or surfaces so the individual LEDs are not visible.
Color Rendering, Appearance, and Consistency
To see colors as intended, the lighting system must produce a desired spectral distribution. Lower color temperatures are associated with “warmer” looking light, appropriate in residential, hospitality, and retail applications. Higher color temperature represents “cooler” looking light, which is appropriate in commercial and industrial applications. Exterior applications show a preference for lower color temperatures (Clanton and Associates and VTTI, 2009, 2010).