Dimmable solid-state light emitting devices

An LED-filament comprising:

• a solid-state light emitter operable to generate blue light with a dominant wavelength in a range 440 nm to 470 nm upon application of electrical power thereto;
• a light transmissive substrate for at least mounting said solid-state light emitter;
• a yellow to green-emitting phosphor associated with the solid-state light emitter to generate light with a peak emission wavelength in a range 500 nm to 575 nm;
• and
• a red-emitting phosphor associated with the solid-state light emitter to generate light with a peak emission wavelength in a range 600 nm to 650 nm,
• wherein a percentage decrease in conversion efficiency corresponding to an increase in blue light photon density exhibited by the red-emitting phosphor is larger than a percentage decrease in conversion efficiency corresponding to the same increase in excitation light photon density exhibited by the yellow to green-emitting phosphor.

A white light emitting device or an LED-filament comprising:

• a solid-state light emitter to generate blue excitation light with a dominant wavelength in a range 440 nm to 470 nm;
• a yellow to green-emitting phosphor associated with the solid-state light emitter to generate light with a peak emission wavelength in a range 500 nm to 575 nm;
• and
• a red-emitting phosphor associated with the solid-state light emitter to generate light with a peak emission wavelength in a range 600 nm to 650 nm,
• wherein the red-emitting phosphor comprises a Group IIA/IIB selenide sulfide-based phosphor material, and
• wherein the white light emitting device is configured such that in operation a reduction in electrical power to the solid-state light emitter of about 90% results in a reduction in CCT of emitted light of at least 700K.

A method of dimming a white light emitting device or LED-filament comprising the steps of:

• providing a solid-state light emitter to generate excitation light with a dominant wavelength in a range 440 nm to 470 nm;
• supplying electrical power to the solid-state light emitter;
• providing a first phosphor associated with the solid-state light emitter to generate light with a peak emission wavelength in a range 500 nm to 575 nm;
• providing a second phosphor associated with the solid-state light emitter to generate light with a peak emission wavelength in a range 600 nm to 650 nm;
• wherein a percentage decrease in conversion efficiency corresponding to an increase in excitation light photon density exhibited by the second phosphor is larger than a percentage decrease in conversion efficiency corresponding to the same increase in excitation light photon density exhibited by the first phosphor;
• and
• decreasing the electrical power to the solid-state light emitter to decrease the excitation light photon density.