Why blue was so hard
Red and green LEDs had been used for decades as indicator lights in electronics. White light needs blue, but nobody could make the material, gallium nitride, in good enough quality. Nakamura, working at the small company Nichia, managed it almost single-handedly and became a legend.
White light
A white LED is actually a blue diode coated with a yellow phosphor. The eye sees the mix of blue and yellow light as white. Display and TV backlights work on the same principle.
When buying
- Colour temperature: 2,700 K is warm light like a traditional light bulb, 4,000 K is neutral and 6,500 K is cool.
- CRI (colour rendering index) above 90 means natural colours.
- Cheap LEDs can flicker, which tires the eyes.