DRIVING AROUND TOWN, it’s probably easy for people in the sign industry to spot differences in LED and fluorescent lighting within signage. As LED-lit signs become more common, it is becoming more important that LED products provide light quality that meets or exceeds that of incandescent and fluorescent lights. LEDs are available in a variety of white shades and hues (known as correlated color temperature or CCT) as well as fidelity (known as its color rendering index or CRI). What role do these metrics play in sign creation?
Color Rendering
CRI represents, on a scale to 100, the ability of a light source to make colors of an object appear natural, as is the case with sunlight. Incandescent bulbs and sunlight have a perfect CRI of 100, while fluorescent sources achieve 75-85 CRI. LEDs can nearly reach 100, but cost more as CRI increases – especially above 90 (values are quoted as a minimum). In indoor lighting, a CRI of 93-98 is recommended for hospitals and museums, where accurate color rendering is demanded.
Otherwise, indoors a CRI of 90+ is recommended to create the most appealing look. With cabinets and channel letters, 80 CRI has been the standard for some time because they are indirect light sources.
High-CRI fixtures reveal subtle color differences in paints and materials in shops such as Creative Sign Designs’ facility in Tampa, FL.
Color Appearance
White light has different “temperatures,” which describe the color appearance of a light source in Kelvin (K). Light sources with lower CCT appear warmer while those with higher CCT appear cooler. Note that the color names (warm white, cool white) sometimes seen on LED products are arbitrary and vary by manufacturer since there is no standard tying color names to particular K values. Outdoor cabinets and channel letters often use daylight white (6500K), since it closely matches noon daylight. Depending on the sign, fabricators choose the most appropriate white for the application and competing signage environment. Interestingly, when a warmer sign is put next to a cooler one, people tend to think the cooler one is brighter, even when it isn’t – a function of our vision.
Using a higher-correlated color temperature makes signs stand out. However, mood is another consideration. A restaurant sign may trend toward warmer CCTs to create a homey, inviting look. Cooler options combined with aluminum portray a cleaner, high-tech look. New LED approaches, particularly in LED strips (in flex/rigid formats), allow tunable versions of white. By combining warm and cool LEDs on a strip, such as 3000K with 5000K, every color in between these temperatures can be created.
The dynamic LED lighting market is driving toward better rendering and various shades of white. Signs everywhere are more beautiful for the changes.