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EP-4739942-A1 - LIGHT EMITTING DEVICE

EP4739942A1EP 4739942 A1EP4739942 A1EP 4739942A1EP-4739942-A1

Abstract

A LED filament comprises an array of a plurality of LEDs arranged on a first major surface of an elongated light-transmissive carrier. The plurality of LEDs is arranged to emit LED light having an emission peak wavelength between 430nm and 490nm. A first encapsulant covers the array of the plurality of LEDs. A second encapsulant covers at least part of a second major surface, opposite to the first major surface, of the carrier. The encapsulants comprise a respective luminescent material comprising a respective green phosphor of different types, arranged to convert at least part of the LED light into respective green phosphor light having different emission peak wavelengths. An emission spectrum of the first green phosphor at least partly overlaps an excitation spectrum of the second phosphor.

Inventors

  • VAN BOMMEL, TIES
  • MALLENS, Erik, Petrus, Johannes

Assignees

  • Signify Holding B.V.

Dates

Publication Date
20260513
Application Date
20240704

Claims (15)

  1. 1. A light emitting diode, LED, filament (100) arranged to provide LED filament light and comprising: an array of a plurality of LEDs (101) arranged on a first major surface (111) of an elongated light-transmissive carrier (102), said plurality of LEDs arranged to emit LED light having an emission peak wavelength in a wavelength range from 430nm to 490nm; a first encapsulant (103) covering said array of said plurality of LEDs (101) and covering at least part of said first major surface (111) of the carrier (102); a second encapsulant (104) covering at least part of a second major surface (112), opposite to said first major surface (111), of the carrier (102); wherein: the first encapsulant (103) comprises a first luminescent material comprising a first green phosphor of a first phosphor type, said first green phosphor is arranged to convert at least part of said LED light into first green phosphor light having a first emission peak wavelength, I; the second encapsulant (104) comprises a second luminescent material comprising a second green phosphor of a second phosphor type that is different from the first green phosphor type, said second green phosphor being arranged to convert at least part of said LED light into second green phosphor light having a second emission peak wavelength, X2, being different from XI; and an emission spectrum (201) of the first green phosphor at least partly overlaps an excitation spectrum (203) of the second phosphor; and wherein: I X2 - XI I > 20nm.
  2. 2. The LED filament (100) of claim 1, wherein: (i) - the first luminescent material further comprises the second green phosphor, wherein the concentration of the first green phosphor in the first encapsulant is at least two times higher than the concentration of the second green phosphor in the first encapsulant, - the second luminescent material further comprises the first green phosphor, the concentration of the second green phosphor in the second encapsulant is at least two times higher than the concentration of the first green phosphor in the second encapsulant, or, (ii) the first encapsulant does not comprise a second green phosphor and the second encapsulant does not comprise a first green phosphor.
  3. 3. The LED filament (100) of any of claims 1 to 2, wherein: the first green phosphor is a broadband phosphor having an emission peak with a full-width-half-maximum of at least 70 nm and the second green phosphor is a broadband phosphor having an emission peak with a full-width-half-maximum of at least 70 nm, or the first green phosphor is a broadband phosphor having an emission peak with a full-width-half-maximum of at least 70 nm and the second green phosphor is a narrowband phosphor having an emission peak with a full-width-half-maximum of less than 40 nm, or the first green phosphor is a narrowband phosphor having an emission peak with a full-width-half-maximum of less than 40 nm and the second green phosphor is a broadband phosphor having an emission peak with a full-width-half-maximum of at least 70 nm.
  4. 4. The LED filament (100) of any of claims 1 to 3, wherein: the first green phosphor is a garnet class phosphor, and the second green phosphor is a garnet class phosphor.
  5. 5. The LED filament (100) of any of claims 1 to 4, wherein: both of the first green phosphor and the second green phosphor comprises one or more of: - LuAG, - LuYAG, - YAG, or - YGdAG.
  6. 6. The LED filament (100) of any of claims 1 to 5, wherein: XI is at least 20 nm larger than X2.
  7. 7. The LED filament (100) of any of claims 1 to 6, wherein: the first luminescent material further comprises a first red phosphor arranged to convert at least part of said LED light and/or at least part of the first green phosphor light into first red phosphor light, and/or the second luminescent material further comprises a second red phosphor arranged to convert at least part of said LED light and/or at least part of the second green phosphor light into second red phosphor light.
  8. 8. The LED filament (100) of claim 7, wherein: the first red phosphor and/or the second red phosphor are selected from the Mn-activated narrow-band class red phosphors.
  9. 9. The LED filament (100) of claim 7 or 8, wherein: the first red phosphor and/or the second red phosphor is a KSiF phosphor.
  10. 10. The LED filament (100) of claim 7 to 9, wherein: the first red phosphor and the second red phosphor are different.
  11. 11. The LED filament (100) of claim 7 to 10, wherein: the first red phosphor is a Mn-activated narrow-band class red phosphors; and the second red phosphor is a Nitride class phosphor and/or an Oxynitride class phosphor.
  12. 12. The LED filament (100) according to any one of the preceding claims, wherein the LED filament light is white light having a correlated color temperature in a range from 1700K to 6500K and a color rendering index of at least 80.
  13. 13. The LED filament (100) according to any one of the preceding claims, wherein the first green phosphor has a first concentration (Cl) in the first encapsulant (103) and the second green has a second concentration (C2) in the second encapsulant (104) different from the first concentration (Cl).
  14. 14. A lighting arrangement (300) comprising at least one LED filament (100) of any of claims 1 to 13 and a controller (302) configured to control the array of the plurality of LEDs (101).
  15. 15. A lamp or a luminaire (400) comprising at least one LED filament (100) according to any one of claims 1 to 13 or the at least one lighting arrangement (300) of claim

Description

Light emitting device FIELD OF THE INVENTION The present invention generally relates to light emitting devices. More specifically, the present invention is related to a light emitting diode (LED) filament comprising an array of a plurality of LEDs arranged on an elongated carrier. BACKGROUND OF THE INVENTION A trend in the development of light emitting devices is LED filament lamps. A LED filament lamp is a lamp comprising LEDs which is designed to resemble a traditional incandescent light bulb with a visible filament for aesthetic and light distribution purposes. In addition to the advantage that LED filament lamps may be configured such that they resemble traditional light bulbs, a further advantage of LED filament lamps is the inherent high energy efficiency of light-emitting diodes. However, there remain aspects of LED filament lamps that allow for further improvements. For example, there is a strong desire to improve the light quality in terms of factors like color rendering index (CRI) and/or having light with a more/improved continuous spectrum and/or improved spectrum that more resembles the spectrum of natural sunlight, as well as improving the energy efficiency of LED filament lamps. US 2020/303355 discloses a. LED-filament includes a partially light- transmissive substrate; blue LED chips mounted on a front face of the substrate; first broadband green to red photoluminescence materials and a first narrow-band manganese-activated fluoride red photoluminescence material covering the blue LED chips and the front face of the substrate; and second broad-band green to red photoluminescence materials covering the back face of the substrate. The LED-filament can further include a second narrow-band manganese-activated fluoride red photoluminescence material on the back face of the substrate in an amount that is less than 5 wt percent of a total red photoluminescence material content on the back face of the substrate. SUMMARY OF THE INVENTION It is of interest to provide a LED filament that is capable of overcoming drawbacks with prior art LED filaments. This and other objects are achieved in a first aspect by providing a LED filament having the features of the appended independent claim. Preferred embodiments are defined in the appended dependent claims. Hence, according to the present invention, there is provided a LED filament arranged to provide LED filament light. The LED filament comprises an array of a plurality of LEDs arranged on a first major surface of an elongated light-transmissive carrier. The plurality of LEDs is arranged to emit LED light having an emission peak, e.g. a dominant emission peak, wavelength in a wavelength range from 430nm to 490nm. The LED filament comprises a first encapsulant covering the array of the plurality of LEDs and covering at least part of the first major surface of the carrier. A second encapsulant is covering at least part of a second major surface, opposite to the first major surface, of the carrier. The first encapsulant comprises a first luminescent material comprising a first green phosphor of a first phosphor type. The first green phosphor is arranged to convert at least part of the LED light into first green phosphor light, e.g. in the wavelength range 510- 580nm, having a first emission peak, e.g. a dominant emission peak, wavelength, XL The second encapsulant comprises a second luminescent material comprising a second green phosphor of a second phosphor type that is different from the first green phosphor type. The second green phosphor is arranged to convert at least part of the LED light into second green phosphor light, e.g. in the wavelength range 510-580nm, having a second emission peak, e.g. a dominant emission peak, wavelength, X2, where X2 is different from XL An emission spectrum of the first green phosphor at least partly overlaps an excitation spectrum of the second phosphor. That is, such an arrangement of the first and second green phosphors provides an overlap between the emission spectrum of the first green phosphor and the excitation spectrum of the second phosphor such that the first green phosphor light is absorbed by the second green phosphor, which in turn emits the second green phosphor light having a different (dominant) emission peak wavelength. This re-absorption of light may result in increasing the amount of green light generated by the second green phosphor resulting in a more uniform light output of the LED filament in both directions. In addition, compared to mixing the first and second green phosphor in one layer, the efficiency is increased as less green light generated by the first green phosphor is absorbed by the second green phosphor, because only a part of the light generated by the first green phosphor is transmitted to the second green phosphor via the substrate. For example, the absolute difference between X2 and I may be greater than or equal to 20nm, preferably 25nm, more preferably 30nm, more preferably 35nm