Moving from CCFT- to LED-backlit LCD modules

Comparing spectral curves

When glancing back and forth between these two spectral curves, the differences become apparent. But it’s when the two sets of spectral curves are superimposed that the differences of the LED backlight’s output become apparent. See Figure 4.

With this overlay, it also becomes even more apparent how the green/yellow portion of the output has been peaked by the manufacturer of the CCFT backlight to gain more apparent brightness; as the eye is most sensitive to the 550 nm (green/yellow) band of light.

When dimming CCFTs many inverter boards offer extended capability, allowing CCFTs to be dimmed reliably to about 5 percent. Some care must be exercised in cold environments, as attempting to dim a CCFT in such environments can greatly shorten its life. LEDs have no such restrictions, as they are dimmable all the way to zero, without restriction of temperature, within the limits of the specifications.

Internal drive circuitry

CCFT-backlit modules smaller than the 12- to 15- inch sizes seldom incorporate on-board CCFT drivers, due to the power-handling needs and isolation problems caused by a CCFT driver sharing a power supply with, and in close proximity to, the panel drive circuits.

On-board LED drivers are far easier to incorporate as a part of the overall panel circuitry, and are often included in all but 'economy-grade' modules.