Illumination of x-rays: the usual lights exposed.

AIMS Faced with pressure of work and limited resource, doctors frequently use the nearest available light to examine x-ray films. The aim of this study was to examine the relative intensities of hospital light sources, and to compare these with the light intensity guidelines (1500 to 3000 candelas) of the British Institute of Radiology. METHODS The relative intensities of seven hospital light sources were examined using a standard light meter at a constant 30 cm from the source. A control group of 10 individual consultant's x-ray viewing boxes were compared with six other ward based light sources. RESULTS Only two light sources approached the British Institute of Radiology light intensity x-ray viewing criteria: the x-ray viewing boxes of consultant radiologists with a median light intensity of 3503 candelas (chi(2)=13.3, df 1; p=0.0001), and daylight from north facing windows with a median of 1464 candelas when overcast (chi(2)=8.571, df 1; p=0.003) and 4669 candelas in sunshine (chi(2)= 6.364, df 1; p=0.0001). CONCLUSION Few hospital light sources met the British Institute of Radiology guidelines. The long held high regard of artists for northern light appears justified even in the environment of a British district general hospital.