Orcam devices use a camera, so like all cameras they require good light conditions. It is best to avoid glare. In low light conditions the LED reading lights will activate automatically to enhance the light levels, however if the light level is too low, or in complete darkness, the device won't be able to recognize the text.
While the devices may be able to read in certain low-light environments, please be aware that the accuracy of the device's reading drops the darker the environment is.