Illuminated keyboard

1. An illuminated keyboard comprising:

a frame plate;

a character keycap connected with said frame plate, and movable upwardly or downwardly with respect to said frame plate;

a light source disposed under said character keycap for emitting invisible light;

a membrane plate;

a switch circuit plate; and

a base plate,

wherein said character keycap, said frame plate, said membrane plate, said switch circuit plate and said base plate are sequentially arranged from top to bottom, and said illuminated keyboard further comprises a luminous portion comprising a luminous substance, which is excited by said light source to generate visible light to irradiate said illuminated keyboard.

2. The illuminated keyboard according to claim 1 wherein said luminous substance is a fluorescent agent.

3. The illuminated keyboard according to claim 2 wherein said illuminated keyboard further comprises an ink layer, and said luminous substance is doped in said ink layer.

4. The illuminated keyboard according to claim 3 wherein said ink layer is formed on a bottom surface of said frame plate at a position right under said character keycap.

5. The illuminated keyboard according to claim 3 wherein said ink layer is formed on a top surface of said membrane plate at a position right under said character keycap.

6. The illuminated keyboard according to claim 3 wherein said ink layer is formed on a top surface of said switch circuit plate at the position right under said character keycap.

7. The illuminated keyboard according to claim 1 wherein said membrane plate is a transparent plastic sheet.

8. The illuminated keyboard according to claim 1 wherein said luminous substance is doped in a material for producing said character keycap.

9. The illuminated keyboard according to claim 1 wherein said character keycap has a light-transmissible character portion, which is defined by coating a surface of said character keycap with an opaque material and then removing a character.

10. The illuminated keyboard according to claim 9 wherein said character is removed by a laser engraving process to define said light-transmissible character portion of said character keycap.

11. The illuminated keyboard according to claim 1 wherein said light source is a mercury vapor UV lamp.

12. The illuminated keyboard according to claim 1 wherein said light source is an UV light emitting diode.

13. The illuminated keyboard according to claim 1 wherein said frame plate has a light-guiding function, a concave structure is formed in a bottom surface of said frame plate, said concave structure is not in communication with a top surface of said membrane plate, and said light source is disposed on said membrane plate and accommodated within said concave structure.

14. The illuminated keyboard according to claim 1 wherein said light source is fixed on said membrane plate via an electrically-conductive adhesive.

15. The illuminated keyboard according to claim 1 wherein said illuminated keyboard further comprises:

a connecting member for connecting said character keycap with said frame plate; and

an elastic member bonded onto said switch circuit plate, so that said character keycap is elastically movable upwardly and downwardly.

16. The illuminated keyboard according to claim 15 wherein said frame plate has a hollow portion, said elastic member is penetrated through said hollow portion, and a curvy profile is formed on an inner wall of said hollow portion.