The dark side of LEDs

The bright light emitted from LEDs could be affecting our health, as Mari Hysing explained to Graihagh Jackson...

Mari - A body clock is the internal biological clock that helps us keep our 24-hour cycle and we need that to have our day and night routines. This body clock is actually controlled by the suprachiasmatic nucleus in the brain helping us keep our circadian rhythm.

Graihagh - How is it affected by light?

Mari - Light is really important to set this body clock. So what it does, in short, is when the eye signals that it’s dark the suprachiasmatic nucleus starts the production of melatonin and that’s the sleep hormone. It’s very important to have good sleep. In the same way as in the morning, the light suppresses the body’s production of melatonin. So, essentially, light keeps us on a good day and night rhythm.

Graihagh - What about different types of light? I’m thinking bluer light, brighter white light and even red light, do they all have a different way in which they interact with our body clocks?

Mari - All light affects melatonin and our body clocks but we know that the LED lighting is even more efficient in that sense so it has a stronger effect on our melatonin production than the other light sources. So what happens is if you have bright light, for example, LED lighting in the evening, you actually delay your circadian rhythm and, instead of being sleepy and going to bed, you feel more alert and you can often end up with too short sleep.

Graihagh - That doesn’t sound like the end of the world - a little bit of lost sleep. Is that really that dangerous or that bad?

Mari - Well, of course, everyone has a bad night’s sleep every once in awhile and that’s not dangerous. But we do know that insufficient sleep over a long period of time is associated with poor mental and physical health. For instance, we know that if you just have a few hours of sleep you are easily irritated, more worried. I think everyone can relate to that but we also know that, for instance, it’s related to depression in the long run.

Another example that we’ve been studying here in Bergen is that if you have short sleep duration, and this was among adolescents, we found that they have poor school performance compared to others. And maybe that’s not surprising when we know that sleep is important for memory and concentration, for instance.

Graihagh - So that was in students that were, presumably, using smartphones and tablets late at night and it was delaying this production of melatonin and, therefore, they were getting to sleep later and still waking up at that same time and they have worse grades? How much worse were they?

Mari - They were significantly worse in the Norwegian grading system, but what we found is that the students between 16 and 18 that went to sleep between 10 and 11, they had far better grades.

Graihagh - So was it as simple as not using screens later at night then?

Mari - Well I guess that’s one solution. Another thing you can do is at least try to log off the last hour before you go to sleep. If you’re not able to log off all the way, there are some of the screens now that you can turn off some of the blue light, so the LED lighting so that at least you have more dim lighting and a light that doesn’t affect your sleep in the same way.

Graihagh - Fantastic. Colin, I just wanted to ask you what the world of LEDs is doing about it? If LEDs are giving off this blue light, yes, we’re putting off this phosphor ping pong balls over the top but there’s still some blue light coming out there. So what are they doing in your industry to compensate for that?

Colin - The receptors in the eyes are most sensitive to the blue light, so the blue light is the problem as you say. So we want to mimic natural sunlight and what we’re trying to do now is instead of having the phosphor, we want to make white light using red, green and blue LEDs, so that’s the obvious way to do it. We haven’t done that so far because green is very inefficient but, if we push the efficiency of green up, it’s called ‘the green gap problem,’ then we’ll have red, green and blue LEDs and people will be able to control the colour quality just as they want. So, if they want a romantic supper, you can have a reddish white light.

Graihagh - Colin, you mention the green gap that these green LEDs are just inefficient in comparison to the blue and red. Why is that?

Colin - Well, they’re more inefficient because to get the green light out, you have to grow at a lower temperature than getting the blue light out, and when you’ve got a lower temperature you have more defects in the crystal, impurities and defects and that quenches the light emission so they’re less efficient.

Graihagh - So this is like when Tom went to go and see Rachel and they talked about the electrons combining with the hole like the Labyrinth game?

Colin - That’s right.

Graihagh - If there are more problems with the structure, then those electrons don’t meet those holes and you don’t produce the light?

Colin - Yeah. The electrons actually go to defects and the holes go to the defects. They don’t combine properly and they don’t give out the light. They give out heat actually rather than light.

Graihagh - Which is exactly what we don’t want!

Colin - But the interesting news is, and this is this week's work right, if you form gallium nitride with a different atomic arrangement, different crystal structure, then we think we can solve this green gap problem. We’re just doing this now so it’s for a future broadcast. But we can see really brilliant green light coming out of this and we just have to measure the efficiency which we haven’t yet done, but within the next four weeks, we’ll do that.

Graihagh - Wow!

Colin - So we think we may have solved this problem. This is really up to date.