LED lamp using blue and cyan LEDs and a phosphor
Many thousands of micro-LEDs (e.g., 25 microns per side) are deposited on a substrate. Some of the LEDs are formed to emit a peak wavelength of 450 nm (blue), and some are formed to emit a peak wavelength of 490 nm (cyan). A YAG (yellow) phosphor is then deposited on the LEDs, or a remote YAG layer is used. YAG phosphor is most efficiently excited at 450 nm and has a very weak emission at 490 nm. The two types of LEDs are GaN based and can be driven at the same current. The ratio of the two types of LEDs is controlled to achieve the desired overall color emission of the LED lamp. The blue LEDs optimally excite the YAG phosphor to produce white light having blue and yellow components, and the cyan LEDs broaden the emission spectrum to increase the CRI of the lamp while improving luminous efficiency. Other embodiments are described.
1. A method of forming a lighting device comprising:
printing a first plurality of light emitting diode (LED) chips on a substrate, the first plurality of LED chips emitting a first peak emission wavelength and emitting blue light;
printing a second plurality of LED chips on the substrate, the second plurality of LED chips emitting a second peak emission wavelength longer than the first peak emission wavelength and generating a light greener than the blue light,
wherein the first plurality of LED chips and second plurality of LED chips are printed on a substrate as an LED ink; and
providing a layer of the same wavelength-converting material over both the first plurality of LED chips and the second plurality of LED chips for converting the blue light and the greener light to longer wavelength light,
wherein light generated by the lighting device is a mixture of blue light from the first plurality of LED chips, greener light from the second plurality of LED chips, and longer wavelengths of light from the wavelength-converting material to create a white light.
2. The method of claim 1 wherein the wavelength-converting material is separated from the first plurality of LED chips.
3. The method of claim 1 wherein the wavelength-converting material is deposited on the first plurality of LED chips.
4. The method of claim 1 wherein the LED ink comprises the first plurality of LED chips and the second plurality of LED chips mixed together in a solvent.
5. The method of claim 1 wherein the first plurality of LED chips emits blue light and the second plurality of LED chips emits cyan light.
6. The method of claim 1 wherein the first peak emission wavelength and the second peak emission wavelength are between about 430-507 nm.
7. The method of claim 1 wherein the wavelength-converting material comprises a YAG phosphor.
8. The method of claim 1 wherein the wavelength converting material comprises a yellow phosphor.
9. The method of claim 1 wherein the first plurality of LED chips is printed separately from the second plurality of LED chips and separately controlled by a current source.
10. The method of claim 1 wherein the first plurality of LED chips and the second plurality of LED chips are mixed together in the LED ink and printed together on the substrate, wherein the first plurality of LED chips and second plurality of LED chips are controlled by the same current source, and wherein the wavelength-converting material is deposited over the first plurality of LED chips and the second plurality of LED chips.
11. The method of claim 1 further comprising controlling the second plurality of LED chips separately from the first plurality of LED chips to adjust an emitted color of the device.
12. The method of claim 1 further comprising controlling the first plurality of LED chips separately from the second plurality of LED chips to adjust an emitted color of the device.