The Backlights for LCD displays are white LEDs, which are made by using a Blue LED together with a yellow phosphor to transform some of the light for the Red and Green primaries. We thought it would be interesting to compare the light spectra of the LCD iPads and iPhone 4 with the OLED display in the Samsung Galaxy S Smartphone.

The spectrum of an LCD display is just the spectrum of its white LED Backlight filtered through the individual Red, Green and Blue sub-pixel filters within the LCD panel. OLEDs are emissive devices so their spectra is just the sum of the individual Red, Green and Blue OLED spectra, modified slightly by the touchscreen layer and anti-reflection absorption layer through which their light must pass.

As expected the OLED RGB spectra are relatively narrow with deep notches between the primaries, which results in highly saturated colors. The LCD RGB spectra are a broader filtered broadband spectrum from the White LEDs, which results in less saturated colors. When more saturated colors are desired, the LCD light output decreases, which then requires more power for the Backlight LEDs. The new iPad has a more extreme Red and deeper notches between the primaries, which gives it greater color saturation than the iPad 2 and iPhone 4.