Further evidence that light damage is mediated byphotopigments was provided by studies in which monkeys wereexposed to different wavelengths to bleach predominantly thepigment in one particular class of photoreceptors. The damage tothe blue cocoretinanmretinaspecies production after 30 min ofblue light exposure. Longer exposures wereaccoreceptorcellwavelength dependency, it has been suggestedthat photochemical damagedepends on the total dose received. This implies that the lightintensity and the duration required to cause a certain level ofdamage are cocoretinal damage. They showed that a 5-minuteexposure does not produce a significant effect, whereas threeand four exposures, each of 5 minute duration and each followedby a 1-hour dark interval, lead to significant damage. However,the cumulative effect does not take place if theretina recoverssufficiently from subliminal damage before the next exposure isapplied. The cumulative nature of light damage has been observedin several subsequent investigationsreceptor damage thancontinuous exposure, and that it exacerbates Class Iphotochemical damage in rats.