OK this is a long way from conclusive. Test on albino rats.
However, the retinas of rats exposed to either blue or cool white9 LED light showed evidence of retinal damage and cell death after 9 days of exposure. Although rats exposed to cool or warm white10 CFL lights also showed some evidence of damage relative to unexposed controls, in general differences were much less pronounced than those observed in the LED-exposed rats. The authors suggest the observed injuries may have been a consequence of oxidative stress from reactive oxygen species that were generated in retinal tissue.3
Blue-light hazard is defined as the potential for a photochemical induced retinal injury resulting from electromagnetic radiation exposure at wavelengths primarily between 400–500 nm. This has not been shown to occur in humans, only inconclusively in some rodent, primate and in vitro studies. The mechanisms for photochemical induced retinal injury are caused by the absorption of light by photoreceptors in the eye. Under normal conditions when light hits a photoreceptor, the cell bleaches and becomes useless until it has recovered through a metabolic process called the visual cycle.
Absorption of blue light, however, has been shown in rats and a susceptible strain of mice to cause a reversal of the process where cells become unbleached and responsive again to light before they are ready. At wavelengths of blue light below 430 nm this greatly increases the potential for oxidative damage. For blue-light circadian therapy, harm is minimized by employing blue light at the near-green end of the blue spectrum. "1-2 min of 408 nm and 25 minutes of 430 nm are sufficient to cause irreversible death of photoreceptors and lesions of the retinal pigment epithelium. ... The action spectrum of light-sensitive retinal ganglion cells was found to peak at 470-480 nm, a range with lower damage potential, yet not completely outside the damaging range." A 2014 study found that LEDs cause retinal damage even in settings where they are used indirectly, such as household light bulbs.
A 2013 in vitro study using shorter blue band spectrum LED lights indicated that prolonged exposure may permanently damage the pigment epithelial cells of the retina. The test conditions were the equivalent of staring at a 100 watt blue incandescent source from 20 cm (8 in) for 12 hours.
Note the problem seems to be more around the 5000K blue or cool lights, not the 2700K ones, where the effect appeared to be less.
It's one to keep an eye on (
) but as a user of the 2700k bulbs I am less worried.