A method of illuminating a reagent test slide having a film portion in a chemical analyzer, which comprises the steps of: - causing two or more light emitting diodes (2, 14, 16, 18) to emit light of substantially the same wavelength simultaneously, each of the two or more light emitting diodes (2, 14, 16, 18) having a semiconductor die and exhibiting a peak in emitted light intensity along a peak light intensity axis extending from the die and exhibiting a non-peak intensity in emitted light which is less than the peak intensity at a non-peak light intensity axis extending from the die which is angularly displaced from the peak light intensity axis; and - positioning the reagent test slide to be illuminated in an illumination plane spaced from the two or more light emitting diodes (2, 14, 16, 18) and so that the angle between the normal to the film portion and the peak light intensity axis of each of the two or more light emitting diodes (2, 14, 16, 18) is greater than zero degrees, the reagent test slide situated in the illumination plane being illuminated by the two or more light emitting diodes (2, 14, 16, 18), the peak light intensity axis of each of the two or more light emitting diodes (2, 14, 16, 18) not being directed at the film portion of the reagent test slide, the non-peak light intensity axis of each of the two or more light emitting diodes (2, 14, 16, 18) being directed at the film portion of the reagent test slide to illuminate the film portion of the reagent test slide, the light simultaneously emitted by the two or more light emitting diodes (2, 14, 16, 18) on the reagent test slide situated in the illumination plane providing a volume of substantially homogeneous irradiance at the illumination plane within which the film portion of the reagent test slide falls. - causing two or more light emitting diodes (2, 14, 16, 18) to emit light of substantially the same wavelength simultaneously, each of the two or more light emitting diodes (2, 14, 16, 18) having a semiconductor die and exhibiting a peak in emitted light intensity along a peak light intensity axis extending from the die and exhibiting a non-peak intensity in emitted light which is less than the peak intensity at a non-peak light intensity axis extending from the die which is angularly displaced from the peak light intensity axis; and - positioning the reagent test slide to be illuminated in an illumination plane spaced from the two or more light emitting diodes (2, 14, 16, 18) and so that the angle between the normal to the film portion and the peak light intensity axis of each of the two or more light emitting diodes (2, 14, 16, 18) is greater than zero degrees, the reagent test slide situated in the illumination plane being illuminated by the two or more light emitting diodes (2, 14, 16, 18), the peak light intensity axis of each of the two or more light emitting diodes (2, 14, 16, 18) not being directed at the film portion of the reagent test slide, the non-peak light intensity axis of each of the two or more light emitting diodes (2, 14, 16, 18) being directed at the film portion of the reagent test slide to illuminate the film portion of the reagent test slide, the light simultaneously emitted by the two or more light emitting diodes (2, 14, 16, 18) on the reagent test slide situated in the illumination plane providing a volume of substantially homogeneous irradiance at the illumination plane within which the film portion of the reagent test slide falls.