An illumination device comprising: a. a light emitting diode arranged to emit LED emission; b. a transmissive support comprising a luminescent material, wherein the luminescent material is arranged to absorb at least part of the LED emission and emit luminescent material emission, wherein the LED and the luminescent material are arranged to generate light of a predetermined color, wherein the luminescent material and LED have a luminescent material to LED distance (dLL) of at least 0.5 mm; c. a translucent exit window arranged to transmit at least part of the light; d. a LED cavity and a diffuser cavity, wherein the LED cavity has a LED cavity side wall and a LED cavity cross section, and the diffuser cavity has a diffuser cavity side wall and a diffuser cavity cross section, wherein the LED cavity is enclosed by an LED support supporting the LED, the transmissive support and said LED cavity wall, wherein the diffuser cavity is enclosed by the transmissive support, the exit window, and the diffuser cavity wall, wherein, relative to the LED, - the transmissive support is downstream of the LED and upstream of the translucent exit window; - the LED cavity is upstream of the transmissive support and downstream of the LED; - the diffuser cavity is downstream of the transmissive support and upstream of the translucent exit window; and - the translucent exit window has an upstream face with an exit window upstream face area, the transmissive support has an upstream face area, and wherein the translucent exit window and the transmissive support have a surface area ratio AEW1/AS1, wherein 1 <AEW1/AS1≤ 20, - and wherein the transmissive support has a transmissive support thickness in the range of 0.1 to 5 mm. a. a light emitting diode arranged to emit LED emission; b. a transmissive support comprising a luminescent material, wherein the luminescent material is arranged to absorb at least part of the LED emission and emit luminescent material emission, wherein the LED and the luminescent material are arranged to generate light of a predetermined color, wherein the luminescent material and LED have a luminescent material to LED distance (dLL) of at least 0.5 mm; c. a translucent exit window arranged to transmit at least part of the light; d. a LED cavity and a diffuser cavity, wherein the LED cavity has a LED cavity side wall and a LED cavity cross section, and the diffuser cavity has a diffuser cavity side wall and a diffuser cavity cross section, wherein the LED cavity is enclosed by an LED support supporting the LED, the transmissive support and said LED cavity wall, wherein the diffuser cavity is enclosed by the transmissive support, the exit window, and the diffuser cavity wall, wherein, relative to the LED, - the transmissive support is downstream of the LED and upstream of the translucent exit window; - the LED cavity is upstream of the transmissive support and downstream of the LED; - the diffuser cavity is downstream of the transmissive support and upstream of the translucent exit window; and - the translucent exit window has an upstream face with an exit window upstream face area, the transmissive support has an upstream face area, and wherein the translucent exit window and the transmissive support have a surface area ratio AEW1/AS1, wherein 1 <AEW1/AS1≤ 20, - and wherein the transmissive support has a transmissive support thickness in the range of 0.1 to 5 mm. - the transmissive support is downstream of the LED and upstream of the translucent exit window; - the LED cavity is upstream of the transmissive support and downstream of the LED; - the diffuser cavity is downstream of the transmissive support and upstream of the translucent exit window; and - the translucent exit window has an upstream face with an exit window upstream face area, the transmissive support has an upstream face area, and wherein the translucent exit window and the transmissive support have a surface area ratio AEW1/AS1, wherein 1 <AEW1/AS1≤ 20, - and wherein the transmissive support has a transmissive support thickness in the range of 0.1 to 5 mm.