Kelvin value for night time?

  • What would be a good Kelvin value for bulbs in the evening for no effect on melatonin?
    Lowest I can find is 2000k - is there much difference between 2000k/2100k/2200k?

  • @zikzak I really do not know, but (I've not tried these) there are 2300K bulbs by Hyperikon that seem to get great reviews. I'm not sure if they have any that have the standard base, I'll look, but for now, here are these: 2300K&qid=1456359289&ref_=sr_1_1&sr=8-1

    Make sure that's the one with the gold base, I'm in darkroom mode and I'm not turning it off to check. It does NOT warm up the color when you dim, but hopefully it will dim quite well. Also look for regular (E26) base bulbs, there are small E12 chandeileir bulbs.

  • Gold base? Do you mean brass?

  • I just ordered a few of these - they are 2000k - I'll see how they are...

  • Oh I can't use those; they're all 240V and we have 120V power. They'd be super dim.

  • @TwoCables I think 12v lighting (if you can get a source to run them) are much brighter than 120v lights. A 25 watt bulb can put off over 320 lumens!

  • @Tungsten_smooth said:


    I don't understand how this relates. The page that zikzak linked to shows 240V light bulbs. They would be very dim on 120V power (probably exactly half their maximum brightness). That's my point.

    So, why are you talking about 12V lighting being brighter than 120V lights?

  • @TwoCables just discussing different voltages.

  • I bought one of these and a few more Calex bulbs - very satisfied... 2000k Ra 99,q_90,w_1280/v1428398771/calex-goldline-xxl-o180-3171.jpg
    It's huge - do a google search for size :)

  • @zikzak The Kelvin value alone isn't what determines the effect on melatonin. It depends entirely on the absolute brightness of the blue-green component of the light hitting your eyes. Colour temperature in Kelvin is basically a measure of the relative mixture of red, green, and blue components, but your body only pays attention to the blue-green. A 25-watt 2700K bulb might have less effect on melatonin than a 60-watt 2000K bulb. You'd have to measure it, for example with a light meter covered with a blue-green filter. It also depends on how far away you're sitting from it, the reflectivity of objects around you, and so on.

  • @Elhem-Enohpi cyan and green are also very stimulating, but after maybe an hour according to harvard research:, blue light starts to affect (delay) sleep more strongly.

  • @Tungsten_smooth Ok, I changed it to say blue-green instead of blue.

    The point is that the Kelvin value is more of a measure of the relative proportions of red, green, and blue in a light source, and in terms of melatonin, your body doesn't care about that. It's sensitive to the brightness and length of time you're exposed to light with a wavelength of around 500 nm (cyan), dropping off as it goes higher or lower than that. The presence or absence of other wavelengths, which is what determines the colour temperature in Kelvin, is more or less irrelevant.

    It's possible for one bulb with a colour temperature of 2000K, and another with 7000K, to have exactly the same effect on melatonin, if they're of different wattages and distances.

  • @Elhem-Enohpi Thanks a lot! That cleared things up a bit for me.. So how can determine what bulbs to buy?
    For instance, I have some Philips Hue bulbs and at night I set them to 2000k and relative low brightness. I always thought I was "safe" in terms of the effect on melatonin but I guess I would have to know their exact combination of wavelengths?

  • @zikzak If you want to be sure that it's "safe" and has no effect on melatonin, set your Hue light to pure red. Otherwise, it's a bit of a guessing game. Even a 2000K light has a certain amount of blue-green or melanopic light in it - about 6% compared to white light, according to f.lux. Whether that has any effect depends a lot on how close you are to it. If you use two bulbs, it doubles your exposure. An Apple 27" screen at 1200K is still too much blue-green light if you sit 12" away, according to f.luxometer, and you need to dim the backlight.

    I suppose there is a certain colour temperature that has virtually no melanopic light, but I think it would be less than 1000K, and look deep orange or red.

    At night I use a single cheap 4-watt 2700K LED bulb. I put an orange filter over it, which blocks 90% or more of melanopic light, and I put it behind a barrier so it's all indirect light bounced off the wall. Seems to work for me.

    The exact combination of wavelengths doesn't matter. Your body's clock is only affected by the blue-green melanopic wavelengths. The other wavelengths aren't really significant either way.

    What's important is:

    1. The absolute strength or power of the blue-green wavelengths.
    2. How far away from the light source you are.
    3. How long you're exposed.
    4. At what point in your circadian cycle the exposure takes place.

    Computer screens are fairly standardized in brightness, and people generally sit the same distance away from them. From that you can get 1 and 2, and you can assume several hours of exposure, late at night, for 3 and 4. Knowing those factors, it's possible to calculate how much f.lux has to dim the blue-green wavelengths of your screen, to get it into a "safe" range of melanopic light, while still not making the screen pure red. The actual colour temperature that turns out to be, is a result of the calculations. For sitting in front of a standard computer screen, it comes to around 2000K.

    Light bulbs are a completely different story. A bulb could be 10 watts or 100 watts. It could be half a metre in front of your face, or five metres behind your back. In terms of the amount of light that hits your eyes, that can mean a difference of several thousand times. So knowing the colour temperature is useless. It doesn't tell you any of the four factors - unless it's so low that the first factor is effectively zero. What you need to know is the melanopic lux, which is a measure of how much blue-green light is arriving at your retinas.

    The only way to really know is to measure the strength of the melanopic wavelengths with a light meter, from your seating position. Most people don't have access to the $15,000 spectrometer that was used to make the f.luxometer simulator, so thankfully you can consult it online to get some ideas. For example, the Philips Hue at 2700K, 30 inches away, and dimmed to 12%, has a melanopic lux of 51.58. That's "good for the office, but too bright after dark", and can cause up to an hour in sleep phase shift if used late at night. On the other hand, setting it to 2000K and/or putting it behind you, may be fine. F.luxometer doesn't let you put those parameters in though, so it's difficult to say without actually measuring it.

  • @Elhem-Enohpi I would say a light that puts out less than 200 lumens, incandescent only, because LED is not standardized at this stage, and used in a lamp on one side of a room should be fine. I've got a couple that do about 120 lumens!

  • @Tungsten_smooth Interesting, what do you base the 200 lumens figure on? So 400 lumens would be too much?

    I have another light I use at night once in a while, its colour temperature is 4000K. I calculated that it puts out about 120 quadrillion lumens. It doesn't seem to bother me. I sit pretty far away from it.

  • @Elhem-Enohpi Thanks a lot for the elaborate answer! You kinda said it already - but this post was so detailed that I got a much better understanding of it. I still feel it's hard to actually know how much the effect is for different scenarios.. I'm not the type of person that feels a big difference from light. I'm very sensitive to light but can't really feel the difference in regards to sleep. I'm trying to be on the safe side though as I have sleep problems in the second half of the night.

    I don't know if you can set Philips Hue to pure red? - it seems some white goes along no matter what color..

    The bulbs they have at would also be a good solution I guess:

  • @zikzak You're welcome! Writing about it also helps me to clarify my own understanding - I still have a lot to learn.

    Yes, it can be difficult to know what level of melanopic lux you're being exposed to from lighting. My approach has been to put a red-orange filter over the light, basically the same as wearing blue-blocking glasses, without the glasses. But that might be too extreme for some people. Don't know what my neighbours think!

    I also have trouble sleeping through the night. Lighting helps somewhat, but I have to do a lot of other things, like trying to eat at regular times, not working too late, not drinking alcohol at night, and not staying up writing long posts on the Internet!

    I've never used a Philips Hue, but in the f.luxometer there's a setting that says "redLED", which appears to be safe at any distance or brightness. Again, it's a bit extreme. I wouldn't like to use a monochromatic red LED light.

    I'm not impressed with LowBlueLights. There's a lot of hype about "the latest in LowBlue LED technology", but they're just repackaging made-in-China monochromatic amber bulbs. They're mainly used in areas where outdoor lighting can endanger sea turtle hatchlings. The light quality is awful, the same as low-pressure sodium streetlamps. Not suitable for indoor lighting. The incandescent and fluorescent bulbs have a yellow-orange coating on them, which is fine I guess, but they seem overpriced. I doubt they actually design any of their own products. Plus their Facebook rant against f.lux is complete bull. I wouldn't give them my money.

    Personally I don't see the need to spend $50-$100 on a "high-tech" light bulb, when you can get the same or better effect using a $5 bulb with an orange sock over it. To each his own though.

  • Haha, yes the last things you mention of things to avoid is probably the hardest and most effectful..

    I originally got Hue because of the possibility to change kelvin signature - I didn't think that I would use the colors. But now I actually use the red quite a lot - before bed, watching movies or sexy time - all very good with the red light. My girlfriend that thought it was a bit weird/cheesy at first now likes it too..

    Good to hear you impression of LowBlueLights. Didn't know they had anything going against f.lux.. And I have had that thought also - that I didn't know what to make of their products in terms of quality and overprice..

    I will try to do the same approach as you mention with a filter. I have some 2700k Ikea spots in my hallway that I would like to soften up a bit.

  • @zikzak I'm using a Rosco Supergel #23 Orange. There might be something better, maybe the #22 or #25, but that's what they had in the shop near me. They give spectrum charts for every filter, on the website. It's quite easy to find, a good photography shop should have it. I paid about $10 for a large roll because I wanted to try putting it over my screen, but that didn't work out so well. Anyway, now I have a lifetime supply. I like the colour, it gives a sort of campfire effect, and I can still make out the colours of things in my room.

  • @Elhem-Enohpi I'd say 200 lumens (and yes 400 is too much) because it's still a lot of light. If you can see fairly well at most brightness levels, than most should be able to adjust to 200 lumens. I think any lower and people would just freak out because it's so dim, they just wouldn't feel comfortable, so then they don't sleep well!

    I just like the number because it's about what most 120v 25 watt incandescent bulbs put out, so it's easy to try. 12 volt 25 watt bulbs can get up to almost 400 lumens! I saw one by "Bulbrite" that got 375! That is truly insane.

  • @Elhem-Enohpi That's great! I just ordered a sample pack of Lee filters - it was free with free shipping also (I'm located in Denmark).

    I can can then check the different amber tones - thanks for the tip! I actually bought some filters before but they were too red for my liking and I kinda gave up because I didn't know exactly what to buy - but with these samples I can get to know what I want :)

  • @zikzak So many to choose from!

    If you download the PDF datasheets for the Lee filters, they show you a chart with the percentages they block for each wavelength. You can compare that with the melanopic response of the eye:

    I looked at a couple, the #020 Medium Amber seems like it might let a bit too much green through, but it could be ok depending on the bulb and the other factors. The #507 Madge cuts off everything shorter than about 560 nm, so that should certainly do the trick on any bulb. The #105 Orange has more yellow and a little bit of green. It's similar to the Rosco #23 Orange that I have, and close to the Uvex SCT Orange filter in the f.luxometer, though with slightly more in the 520 nm area. The Uvex brings the Cree 2700K at 100 lux to an acceptable level according to the f.luxometer. If you're putting it over a 2700K bulb, a lot of the blue has been removed already.

    Let us know how the experiment goes!

  • @Tungsten_smooth Ok, I thought maybe you had figured out the melanopic lux exposure a 200 lumen incandescent bulb would produce in an average room. That could actually be useful to know. So it's more of a guess then. By the way, I did calculate that a full moon actually produces about 120 quadrillion lumens. Just goes to show you that it's the lux that counts. Otherwise I guess it would be called f.lumens.

  • @Elhem-Enohpi Ah yes, lux is much more meaningful than lumens! Lumens is basically at the source, and lux is what you see, which can be 1/5 or less the originating source.

  • @Tungsten_smooth It can be 1/120 quadrillion, if the originating source is 363,104 km away! A full moon produces maximum 1 lux on Earth.

    If it's not focussed into a beam, a light's brightness drops off with the square of the distance. A light ten feet away is only 1/100th as bright as it is one foot away. That's not counting all the light bouncing off the walls and objects of a room though, which is more difficult to calculate.

  • @Elhem-Enohpi Oh wow, that's a huge difference! I've read herf mention it several times, but I'm not sure how to calculate it. 10 feet makes a difference of 100x! That's just crazy, and a really good thing.

  • @Tungsten_smooth It's true if there's nothing else reflecting the light towards you, like looking up at a light in a dark sky.

    If you're in a room, a lot of light is bouncing around. You basically need a computer simulation that knows how reflective everything is to calculate it then, like the "raytracing" that computer graphics and video games do.

    Or, measure it with a light meter.

  • @Elhem-Enohpi I think a dim light keeps walls quite dim. Not too dark, but dim enough to say that I don't worry about it's affect on sleep. I'll usually cut down to 20 watts or less of incandescent light. I have moderately dark walls, and I block out all the light tresspass from the streetlights. I guess it would be interesting to know how many lux I see in different locations but I know that it's below 15.

    In the daytime (right now!) with more than one window in my room, I've got 13 lux measured to the ceiling. It's sunny but it's not noon, I'll top out at maybe 35. That's really dim--so I have no doubt that a dim light will be considerably less.

  • @Tungsten_smooth What are you measuring that with?

  • @Elhem-Enohpi Note 3 light sensor.

  • So I messed around with the filters - there are some nice possibilities. But it'll cost me too much anyway if I'm gonna put on dimmers. So I'll go with some more Hue bulbs. After all they are very convenient. I stumbled over this - and it sounds quite good since my purpose with them is mainly night lighting:

    herf f.lux team
    4 months ago

    The Hue is RGB, so it's more like a computer monitor than like a warm-white/cool-white mixture.

    I have some data that suggests the Hue is generally extremely low melanopic impact - so for an equivalent color temperature, it has less impact than lights that look similar.

    This makes it hard to get a good daylight from it, but for night time lighting it is extremely good. The red is over at 626nm, so a red setting on Hue shows no blue light at all.

  • @zikzak According to f.luxometer, a Hue set to 2700K has slightly less melanopic lux than a 2700K Cree LED or a standard incandescent of the same brightness, but slightly more than a CFL bulb. The difference isn't really significant. So I don't think I'd agree that the Hue has "generally extremely low melanopic impact", it seems about the same as other lights with equivalent colour temperature.

    As I said though, I have no experience with the Hue. It seems terribly expensive to me, don't they cost around 500 DKK per bulb? A 120x50 cm sheet of Lee filter on that site is 68 DKK, and a normal dimmer switch that can do multiple bulbs is maybe 100 DKK or so, no? Certainly less convenient though, if money is no object...

    I can't read what you wrote that you stumbled across, something posted by herf?

  • The thin that herf wrote was this: "The Hue is RGB, so it's more like a computer monitor than like a warm-white/cool-white mixture.



  • And yes Hue is very expensive - but dimmers a quite expensive also - they are around 250 DKK for the ones implemented in a switch. The ones you can put in the cord are cheaper but makes a hissing sound and usually of mediocre quality. But still Hue is expensive - usually they go for 1000 DKK used for a set with 3 bulbs. That is pretty decent. And the versatility you get is pretty nice I think. Different colors, dimmable, turns on/off when you leave/come home etc. is actually quite usable although I didn't think I was gonna use it to start with.. One annoying thing is that you can't set a custom color/brightness when you turn them on from a switch...

  • @zikzak No idea why he would say that, since his own f.luxometer data shows that it actually has more melanopic impact than a CFL bulb of the same brightness and colour temperature. If you dial it down to red-orange, that's different.

    You can get cheap in-wall dimmer switches for half the price you mentioned if you shop around, I don't know about the quality though. I don't use them. I suppose it would be nice if my lights would magically dim and change colour, but it's a luxury I can't justify on my budget.

    A friend paid a lot of money for the original Hue lamp years ago, and was constantly fooling around with adjusting the colour from purple to green or whatever. I found it quite annoying. Thankfully the novelty wore off and it doesn't get used anymore. Sometimes versatility is overrated...

    My main concern is not to be kept awake at night. Switching to the small orange-filtered lamp a couple of hours before bed seems to be fine, and the colour is pleasant enough. It's a cheap and simple solution. I don't worry about the lights in the hallway etc., because I don't spend enough time there for it to make a difference.

  • @zikzak You can get a plug in lamp dimmer from Lutrom for $10 USD. You can get a rotary dimmer that goes into the wall switch for less than $10 USD. Prices may vary by location, but you should be able to find these things for very low prices.

  • Thanks guys.. Haha I feel like I'm going over to the enemy with Hue ;) Anyway I found a starter set for 750 DKK - half price. Maybe I can even sell the hub thing for 100 DKK - so a pretty good deal. And I do like the Hue - I don't mess too much around with it - I just have 2 or 3 settings I like.. The fact that you cannot turn it on from a physical on a specific setting i just stupid though..

  • @zikzak said:


    F.lux is designed to work with Philips Hue. It's in the "Extras" menu.

  • I have the Philips Hue color lights and I'm very happy with them so I thought I'd share how I have them set up with F.lux on my Windows desktop computer and my Amazon Echo in the event anyone reading this might benefit from it.

    So I have the Philips Hue lights programmed to turn on automatically when the sun sets through an If This Then That recipe on The recipe works with the Weather Channel and it knows my location so once the sun sets, it then triggers the Philips Hue Channel to send instructions to my Philips Hue bridge, which turns on all the Philips Hue lights in my apartment. The color of the lights is the standard bright white that those lights emit if a color isn't chosen, but that's okay (for me) since it's just providing light when walking in the door.

    Once inside, though, I turn on my Windows desktop computer and F.lux overrides the system and changes the color of the lights to what can only be described as a soothing yellow/orange glow much like that soothing glow of a Himalayan salt lamp. (I have no idea how it does this, but I'm very happy with it and it's very relaxing. And it even dims as the night progresses.)

    The problem I encounter, though, is that I don't always have my computer on, so once the computer goes to sleep or turns off, the Hue lights then remain at that level of brightness until I change them or turn them off. It's not a big deal, but after reading this forum and learning that red light doesn't affect our circadian rhythm like blue and green does, I made another recipe on IFTTT recipe for a darkroom mode. The Amazon Alexa Channel listens for my trigger word, which is darkroom, and it instructs the Philips Hue Channel to change the color of all my lights to red. (The Philips Hue Channel allows you to name a color as well or use a CSS hex code. I tried a variety of them and settled on this one: #A00000.)

    So now, about an hour before going to bed I tell my Amazon Echo: "Alexa, trigger darkroom." And she changes all the lights to red. I feel the difference just like someone else mentioned here about how it made them feel and that's now my nightly routine. But hopefully, once F.lux becomes fully functional I won't have to do this and it will just take care of it all.