Lighting design is the practice of knowledgably, and often artfully, combining the necessary lighting qualities needed for a particular project. Some aspects of lighting quality, such as providing the right amount of light, are easily standardized, measured and calculated. But many aspects of lighting quality are either hard to measure, like glare, or primarily subjective, such as aesthetics.
With LED light sources replacing legacy sources in most applications, it is critical to address LED lighting quality. There are a number of ways in which LED’s remain inferior to legacy light sources.
1. GLARE The luminance of a bare high-power LED module is roughly 250 million candela per square meter. This is about 10,000 times the brightness of a T5 lamp and 1/6 the brightness of the sun. Glare shielding is essential in all applications; sadly, far too many LED products, especially high-bay and outdoor products, provide no shielding at all.
2. COLOR TEMPERATURE Kruithof’s curve tells us that the acceptable color temperature of a light source varies with the scene’s light level. LED lighting is often too “cool” for the application. For instance, outdoors most LED lighting should be less than 3000K. There is seldom a good application for LED’s over 4000K, yet many companies, even supposedly good ones, promote 5000K and higher.
3. COLOR QUALITY Good color rendering is possible with LED’s, but usually not provided. We should demand CRI 90 or higher for most applications. Even outdoors, poor color rendering results in gray skin tones. Why would we choose to have inferior lighting products when we don’t have to suffer them?
4. STROBOSCOPIC FLICKER A high percentage of LED luminaires employ cheap drivers or dimming circuits that create 120 Hz flicker. This flicker was found to cause headaches and other problems with fluorescent lamps, and many LED’s are worse. There is no excuse for this.
5. POOR DIMMING PERFORMANCE To replace incandescent lighting, an LED product should “fade to black”. Very few fade below 10%, which to the human eye seems like 25-40% light. Better dimming is critical to making LED products acceptable to the public in homes, hospitality and businesses.