Stuff published an article recently (opens new window) about the dangers of LED light bulbs, arguing that the blue light from LED bulbs disturbs our circadian rhythm and disrupts our sleep, with wide ranging knock-on effects to our health. My skeptical radar beeped at reading this, as I’ve looked into this issue in the past and found much speculation and very little actual science, even though every digital device these days seems to have a night mode for reducing blue light emission from the screen.

However, the article mentioned a study from Australia, and actually included a link (opens new window) - which is unusual. The linked study was "interesting", as the researchers attempted to guesstimate melatonin suppression in study participants by attaching a "spectrophotometer" to them, rather than actually measuring the melatonin levels in their blood or urine. Their conclusions about the effects of the light, because they weren’t actually measuring levels of melatonin, were purely based on numbers they derived from elsewhere. Because of the huge variation in how much blue light suppresses melatonin in different people (a 50x difference between the most and least sensitive people), variation in people’s sleep patterns and their lack of direct measurements, when they tried to correlate evening blue light exposure and people’s ability to sleep they found that the variance in their unknowns swamped the data, and no useful results could be gleaned. So, basically, the study was practically useless when used to work out if blue light in the evening causes people to have worse sleep.

On top of reading this study, I searched google for reputable sources. I found an informative page (opens new window) on the Ministry of Health website which warned about blue light at night. However, of the three external links they gave to support their claim, only one of them actually made any claims about blue light being bad for you - on the Royal Society of NZ’s "Blue light Aotearoa (opens new window)" project page. The other two links, to the International Commission on Illumination (opens new window) and the European Commission (opens new window), both concluded that there is no risk from the blue light emitted by LEDs:

"The CIE considers that the "blue light hazard" is not an issue for white-light sources used in general lighting, even for those that are blue-enriched… The term "blue light hazard" should not be used when referring to circadian rhythm disruption or sleep disturbance."

"There is no evidence that the general public is at a risk of direct adverse health effects from LEDs when the lights are in normal use"

This is not to say that blue light is not a problem - there are real concerns with the blue light given off by arc welders, for example.

Although I wouldn’t consider this matter to be settled, it looks likely that these blue light warnings are premature at best, and likely to be needlessly worrying people. At worst, they are being used by companies, despite a lack of any solid evidence, to sell overpriced screen filters, tinted glasses and warm white LED bulbs from companies like OSIN Lighting (opens new window), a new startup in New Zealand who just happen to be mentioned in the Stuff article.