A radiation generating system comprising a radiation unit, wherein said radiation unit comprises a light source, a first collimator, and an optical arrangement, wherein: - said light source is configured to generate light source radiation having a first spectral power distribution having an intensity I 1,1 at a first wavelength λ 1 and an intensity I 1,2 at a second wavelength λ 1 - said first collimator is configured in a light receiving relationship with said light source, wherein said first collimator is configured to collimate said light source radiation into collimated light source radiation having an initial spatial light distribution (ISLD); - said optical arrangement is arranged downstream of said first collimator and comprises an optical filter and a diffuser, wherein: - said optical filter has a higher transmission for said first wavelength λ 1 than for said second wavelength λ 2 when irradiated under a predefined angle θ; - said first wavelength λ 1 is selected from the range of 190-230 nm and said second wavelength λ 2 is selected from the range of 100-190 nm and/or 230-300 nm; - said optical filter is configured to filter at least part of said collimated light source radiation into filtered radiation comprising at least portion of said light source radiation of said first wavelength λ 1 having a first spatial light distribution and at least portion of said light source radiation of said second wavelength λ 2 having a second spatial light distribution different from said first spatial light distribution; - said diffuser is configured downstream of said optical filter; - said diffuser is configured to diffuse at least part of said filtered radiation into diffused radiation comprising at least a portion of said light source radiation of said first wavelength λ 1 having a third spatial light distribution and at least portion of said light source radiation of said second wavelength λ 2 having a fourth spatial light distribution different from said second spatial light distribution, characterised in that said radiation generating system further comprises a second collimator being arranged downstream of said diffuser; wherein said second collimator is a reflective collimator configured to collimate said diffused radiation into arrangement radiation having a narrower spatial light distribution than said diffused radiation. - said light source is configured to generate light source radiation having a first spectral power distribution having an intensity I 1,1 at a first wavelength λ 1 and an intensity I 1,2 at a second wavelength λ 1 - said first collimator is configured in a light receiving relationship with said light source, wherein said first collimator is configured to collimate said light source radiation into collimated light source radiation having an initial spatial light distribution (ISLD); - said optical arrangement is arranged downstream of said first collimator and comprises an optical filter and a diffuser, wherein: - said optical filter has a higher transmission for said first wavelength λ 1 than for said second wavelength λ 2 when irradiated under a predefined angle θ; - said first wavelength λ 1 is selected from the range of 190-230 nm and said second wavelength λ 2 is selected from the range of 100-190 nm and/or 230-300 nm; - said optical filter is configured to filter at least part of said collimated light source radiation into filtered radiation comprising at least portion of said light source radiation of said first wavelength λ 1 having a first spatial light distribution and at least portion of said light source radiation of said second wavelength λ 2 having a second spatial light distribution different from said first spatial light distribution; - said diffuser is configured downstream of said optical filter; - said diffuser is configured to diffuse at least part of said filtered radiation into diffused radiation comprising at least a portion of said light source radiation of said first wavelength λ 1 having a third spatial light distribution and at least portion of said light source radiation of said second wavelength λ 2 having a fourth spatial light distribution different from said second spatial light distribution,