<instructions>Your goal is to analyze the following comment and estimate how highly it will be upvoted by the Hacker News community.</instructions><comment><author>tzs</author><text>Sort of OT, but this reminds me of a question I&amp;#x27;ve not been able to find an answer for on blue light and sleep. (OT because the article says nothing about blue light).&lt;p&gt;One way light affects sleep is via the intrinsically photosensitive retinal ganglion cells (ipRGCs). These are a third kind of photoreceptor in our retinas, distinct from the more well known rods and cones. These are most sensitive to blue light. They signal the suprachiasmatic nucleus (SCN) in the brain with information about the amount of light they are receiving. The SCN controls circadian rhythms, and uses the changes in light  as the day ends as reported by the ipRGCs to do things like to keep things that should be synchronized to the day&amp;#x2F;night cycle in sync.&lt;p&gt;Blue light in the evening can mess this up because it makes it look like it is still daylight, as far as far as the SCN can can tell from what it gets from the ipRGCs.&lt;p&gt;What I have not found anywhere is whether this is based on absolute or relative amount of blue light. Does the SCN look for blue light to fall below a certain fixed threshold, or does it do something like note the peak level of blue light during the day, and then look for the blue light to fall below a certain fraction of that?&lt;p&gt;The reason this matters is that more and more of our devices that we want to use in the evening supply blue light. We try to counter that by adding features that change the color spectrum in the evening to something with less blue. But that doesn&amp;#x27;t always work. Computers usually can do it, and often so can tablets and phones. I don&amp;#x27;t think many TVs have such a setting, though.&lt;p&gt;If the SCN works with absolute levels, fixing the devices (or wearing blue light filtering glasses) might be the only answer if you aren&amp;#x27;t able to stop using your devices in the evening.&lt;p&gt;But if it is based on relative levels, keyed off the peak daytime level...then instead of fixing all the devices it might be possible to address the problem by greatly boosting blue levels in the middle of the day, so that your evening device levels will be far enough down from the peak to not affect anything.</text><parent_chain></parent_chain></comment><story><title>Sleeping in rooms with even a little light can increase risk of depression</title><url>http://abcnews.go.com/Health/sleeping-rooms-lighting-increase-risk-depression-study/story?id=53636492</url></story>
<instructions>Your goal is to analyze the following comment and estimate how highly it will be upvoted by the Hacker News community.</instructions><comment><author>davidw</author><text>One thing I miss from Italy are &lt;i&gt;real&lt;/i&gt; shutters:&lt;p&gt;&lt;a href=&quot;https:&amp;#x2F;&amp;#x2F;blog.therealitaly.com&amp;#x2F;2007&amp;#x2F;08&amp;#x2F;09&amp;#x2F;window-technology&amp;#x2F;&quot; rel=&quot;nofollow&quot;&gt;https:&amp;#x2F;&amp;#x2F;blog.therealitaly.com&amp;#x2F;2007&amp;#x2F;08&amp;#x2F;09&amp;#x2F;window-technology&amp;#x2F;&lt;/a&gt;</text><parent_chain></parent_chain></comment><story><title>Sleeping in rooms with even a little light can increase risk of depression</title><url>http://abcnews.go.com/Health/sleeping-rooms-lighting-increase-risk-depression-study/story?id=53636492</url></story>