The use of low light intensities in the commercial rearing of turkeys in windowless houses is a controversial issue. Where light intensities are lowered to minimise injurious behaviour without the need to beak-trim birds, welfare is improved. Some reports indicated that the higher levels of light intensity used were associated with more deaths due to cannibalism. On the other hand, some of the lower levels of light intensity used commercially were found to result in eye abnormalities, leg abnormalities, substantially reduced activity levels, increased adrenal gland size and suppression of normal behaviour. A light level which allows normal development and normal behaviour is required, and, in order to provide this without there being injurious behaviour, some modification of housing conditions may be needed.