A method comprising: guiding light from a plurality of light sources of an optical device to a light source analyser; optically detecting optical output states of the plurality of light sources of the optical device over a test interval between a test start time and a test end time; for each light source, optically detecting that the output state of the light source has changed from a first optical condition to a second optical condition, wherein determining the change from the first optical condition to the second optical condition comprises comparing a parameter of received light to a predetermined threshold value; for each light source, optically detecting that the output state of the light source has changed from the second optical condition to a third optical condition, wherein determining the change from the second optical condition to the third optical condition comprises comparing a parameter of received light to a predetermined threshold value; for each light source, determining a first time interval wherein determining the first time interval comprises determining an interval between the test start time and the change from the first optical condition to the second optical condition; for each light source, determining a second time interval wherein determining the second time interval comprises determining an interval between the change from the first optical condition to the second optical condition and the change from the second optical condition to the third optical condition; for each light source, determining a third time interval wherein determining the third time interval comprises determining an interval between the change from the second optical condition to the third optical condition and the test end time; determining a test result for the device based on a comparison of the first, second and third time intervals with pre-stored time intervals, wherein each of the first, second and third optical condition comprise at least one of a light intensity, a colour of light, a wavelength of light, and/or a frequency of light. guiding light from a plurality of light sources of an optical device to a light source analyser; optically detecting optical output states of the plurality of light sources of the optical device over a test interval between a test start time and a test end time; for each light source, optically detecting that the output state of the light source has changed from a first optical condition to a second optical condition, wherein determining the change from the first optical condition to the second optical condition comprises comparing a parameter of received light to a predetermined threshold value; for each light source, optically detecting that the output state of the light source has changed from the second optical condition to a third optical condition, wherein determining the change from the second optical condition to the third optical condition comprises comparing a parameter of received light to a predetermined threshold value; for each light source, determining a first time interval wherein determining the first time interval comprises determining an interval between the test start time and the change from the first optical condition to the second optical condition; for each light source, determining a second time interval wherein determining the second time interval comprises determining an interval between the change from the first optical condition to the second optical condition and the change from the second optical condition to the third optical condition; for each light source, determining a third time interval wherein determining the third time interval comprises determining an interval between the change from the second optical condition to the third optical condition and the test end time; determining a test result for the device based on a comparison of the first, second and third time intervals with pre-stored time intervals, wherein each of the first, second and third optical condition comprise at least one of a light intensity, a colour of light, a wavelength of light, and/or a frequency of light.