As you know, winter is coming. For a lot of people this means that Seasonal Affective Disorder is beginning to set in. [Luke]’s mom already has a light therapy box. It’s one of those commercially available ones that uses fluorescent bulbs and leaves a lot to be desired in the full-spectrum light simulation department. [Luke] jumped on the opportunity to design a better one.
The standard of quality for light therapy units is a rating of 10,000 lux. While lux definitely matters, the rating is a misleading selling point when given on its own. One of the other important factors in mimicking the sun is the Color Rendering Index (CRI). CRI is basically a rating of the bulb’s ability to imitate the color reproduction of natural daylight. The ratings run from 0 to 100 but in reality, the highest-rated bulbs of any kind top out around 98.
For all the fluorescent bulb-bearing light therapy units out there, those bulbs have pretty low CRI ratings. [Luke]’s project page provides emission spectra graphs for a number of bulb types, and we can see how his choice of ceramic metal halide bulbs stacks up against fluorescent, incandescent, and LED bulbs. One of the few downsides to this type of bulb is that they have long startup times.
He ended up making two light therapy lamps, one of them directional and the other omni-directional. They both use ballast-controlled ceramic metal halide bulbs. The ballasts are necessary to provide the high starting voltage that these bulbs require. The omni-directional light is built into a large hurricane candle holder. A lamp holder is fixed into the base and wired to an external ballast box. The directional lamp is a self-contained unit, and [Luke] is happiest with this one. It’s flat and rugged so it can be placed on top of a bookcase and the light bounced off of the ceiling for pleasant, indirect coverage.
We’ve seen a couple of alarm-clock wakeup light builds here, and we’re thinking this would make an awesome mashup.
Interesting note about CRI, it is a very misleading number, it is actually an average of how well multiple test colors are reproduced. The human eye is mainly concerned with the R9 value and the others have less visual effect (affect?). An early dirty trick in cheap LED lighting was to have technically correct CRI with very low R9 values. Based on my experience I would be suspicious of an LED claiming a 98CRI like the article mentions…but they do exist from a few manufacturers.
https://www.youtube.com/watch?v=L3LWXznJx_0
I reference this review with regards to high CRI leds and where to get them. He does a test with an el cheapo version and on of the Yuji chips.
I was quite amazed at the difference!
I was under the impression that light in the blue end of the spectrum was more effective in SAD? Maybe I miss heard though. Still great project and great son.
As I understand it, that’s one of the reasons that higher CCT, more blue and less red, light sources are not the best choice for living areas. They trick your brain into thinking it’s earlier in the day, in theory the CCT on natural light at noon is 6500°K; whereas lower CCT light sources mimic sunset.
From my understanding traditionally blue light was thought to be the best but newer studies are showing green or white light may be better. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4414925/
For my design I tried to match the sun’s emission spectra at mid day, which would ideally also land on a color temperature of 5500K but I was unable to find any high lumen, high CRI ceramic metal halides above 4,200K.
I heard those MH lamps tend to explode. How safe such device, taking in account your face will be very near to it?
http://www.lrc.rpi.edu/programs/nlpip/lightinganswers/mwmhl/safetyIssues.asp
The bulb in the directional fixture is within a metal halide rated lamp fixture so that should be okay in a bulb blowout. I think bulb explosions are much more common in HID bulbs like xenons than metal halide but it was very hard to get good data on this. I would love to find some good data on what type of fixture is needed to contain a blowout on a non-protected (non-open rated) rated bulb.
For the omnidirectional lamp build I put the bulb inside a “hurricane” candle holder since the bulb I used was not rated for an open housing. I don’t know the ratings needed on the glass to contain a blowout so what I used may not be sufficient. If I were to do it again I would use an open rated / protected bulb such as:
http://www.lighting.philips.com/main/prof/lamps/928086209230_EU/product
http://www.lighting.philips.com/main/prof/lamps/928601171701_NA/product
Seasonal Affective Disorder ? Doesn’t sound like a real disease but just the blues everyone got on November…
Hi perry here
SAD is real. My wife has it.
In her crafting area I have 12 32w florecents plant growing tubes.
as sell as 2 different uv lites on timers.
she uses more power lighting up her area then the hole house put together.
Fall is a very hard time around here.
perry here again.
I for got to give the size of her room. it is 12 x 10.
Thanks N have a good day every one..
12 x 10 cm…. your wife must be an ant.
Where does he give the units? Maybe he is used to these weird imperial units with the double prime thingies. Then his wife could be a hamster or something. Or he is talking about Meters and his wife is the wife of a rich man, living in a mansion …
(Intentionally making sexist assumptions, to point out the ridiculousness of the unit assumption;)
@Knargo
You forgot the positional notation. 12×10 might be hexadecimal or base 42 (like all life) then its 44×42 in decimal :D
Sorry for reporting Knargo. There should be reply button in that corner or verification question before submission.
you have no idea
SAD is very real
for those of us that have to deal or hibernate, it is the worst thing ever and I don’t have to deal with snow.
Although the whole “winter wonderland” thing sounds kinda “cool” from a photographers point of view, I’m told by my net-friends in the northern hemisphere the novelty wears thin pretty fast.
I used to have a dozen 4′ full spectrum flouros in my work room, it “kinda” helped, but I still had to sorta, kinda, compensate with 5 dogs and a 8 – 10km walk, every day.
SAD seriously sucks
Fish tanks, I use live plant tanks the lighting is in the right spectrum. As a bonus I get to look at my tanks
I think you spelled “pretty fast” incorrectly. I believe the correct spelling is “instantly”. Every day we go without the first snow coming is a glorious day to me.
How about using multiple LEDs with different spectral emissions to create a mix of light that better matches the sun’s specturm. With this method it would also be possible to change the mix of light to match the changing spectrum of light through out the day. In fact, thinking about it, I believe there are some fish tank lights that already do this to help improve the health of your fish.
Sure. Aquariums were my introduction to both high-CRI and high-PAR (Photosynthetically Active Radiation) lighting.
I can’t remember their name right now, but there used to be (maybe still is) a commercial builder of custom aquarium lights who had a nice online app. You’d pick any combo of various white and colored LEDs, and it would compute the overall CRI and PAR. CRI of up to 98 was achievable.
I built a simple LED fixture, and though I limited the number of supplemental colors, it came out pretty nice. But it still doesn’t beat my T5 fluorescent DD Giesemann Aquaflora/Midday combo for having a sunlight-like look and pleasing color rendition (regardless of CRI and actual color accuracy).
My next build will be with remote phosphors. Their property of converting royal blue to a white approximation, while simultaneously diffusing other colors in mostly unchanged, is supposed to make for a very uniformly colored light source. Some LED light bulbs already use this technique, blending in a bit of red to achieve relatively high CRI. There’s still a large gap in the aqua (blue-green) region though. I don’t know if one were to add that, whether the phosphor is selective enough to pass that significantly unchanged. There are some commercial photography lights using remote phosphors and LEDs that achieve incredibly accurate sunlight reproductions, so I know it’s possible. I just don’t know how many colors they’re blending, and in what proportions. I’m hoping I can manage something nice with only three, four tops, and therefore minimal complexity.
Interesting stuff Chris, you’ve just made me aware of remote phosphors which could really help me solve a different problem I have with illumination inside the vacuum chamber of an electron beam welder. Cheers!
Cool application! If you haven’t hunted down details yet, Intematix seems to be the most accessible manufacturer, with Digikey the major direct-to-public supplier in the US. They have some good datasheets and app notes. I haven’t yet contacted Intematix directly to see how friendly they are to hobbyists, I haven’t had a need to.
Hobbyist level examples are sparse so far. It seems cannabis growers are the most familiar with the product, but the signal-to-noise ratio on their forums is so poor I’m not sure that’s much use. Some laser enthusiasts have experimenting with them too, I saw one illuminated by a high power blue laser pointer, that was dazzling. There’s a car manufacturer, I think it’s Audi, who is working on headlights built like this. They spin the phosphor to avoid overheating it in one spot, much like the electron beam target in high-power xray tubes.
Kristina, are you a stark?
According to this quiz, yes.
I simply moved from the frozen north to southern California. Nothing beats going outside on these short days. Oh look, the sun is shining right now, I think I’ll go for a walk.
Since I live in Florida it’s not a problem. I think salt water fish tank lamps or some of the newer led or high output
fluorescent (65000 K) might work well. Vitamin D is what we lack in the winter so supplementing D3 is a must.
Don’t OD on D3.
It’s hard to find a business that wants to be lit with sodium light anymore. That “halloween” color is ugly. These lights have been the preferred light for some time now. This project is good for workshop, studio, etc. anywhere you want good color. I am just waiting for the spooky lights to flee from our town soon like they have in some smaller towns around.
My wife suffers SAD and I promised her that I would build her one (or more) lights to combat it. I toyed with using metal halide but the ballast requirements and the potential for bulb explosion all but nixed that idea. So I’m going to use an array of high-CRI Bridgelux LED COBs.
The trick, though, is achieving the necessary 5000 lux-hour rating. I’m not sure if lux-hour is an established unit of measurement but I’m going to use it. Various papers seem to have established empirically that you need 10000 lux *at the eye* for 30 minutes or 5000 lux for an hour, etc. My and my wife’s plan was for her to use this light for 30-45 minutes in the morning before work so we need to be on the higher end of the lux-time scale (since her job involves lots of meetings, it wouldn’t be practical to set up a lower-lumen light at the office so that she could hit 5000 lux-hours over a period of hours)
Okay. Since lux follows an inverse square relationship, 10000 lux requires an a lot of lumens if A) the light source is more than a foot or two away and B) isn’t a narrow spotlight. And if you’re going for 10000 lux at-the-eye of indirect light (eg. reflected off a white ceiling or wall), you need an utterly ridiculous number of lumens that will depend on the ceiling’s albedo.
Some back-of-the-envelope estimates that I made last week for a wide-angle floodlight (eg. using the LED COB’s 120-degree emission angle with no reflector) that’s positioned to shine directly on my wife suggest that I need upwards of 20,000 lumens in order for the light fixture to not be located intrusively closeby. I haven’t done any calculations for indirect ceiling-bounced light but I have no doubt that I’d need in excess of 150,000 lumens in order to achieve 10000 lux at the eye even in a small room. At that point, keeping the LEDs cool would be a challenge in itself.
The hardest part, though, has been coming up with a suitable housing and light fixture (actually, I’ll probably split it into a pair of fixtures) that’s at least somewhat aesthetic…Still looking…
The high 97 CRI BXRA3 Bridgelux Decor Ultra High CRI Array Series LEDs max out at 3500K but the light output is a good start at 5530 lumen. Ultra high CRI LEDs have a lower lumen/watt efficiency than metal halide but that is not a big issue for this application. The 3500K is a little low of a color temperature for light therapy but the CRI is great. They are $72 a pop at digikey which will add up quick. With two of them you should be able to hit 10,000 lux at a distance of probably around 12-18 inches. Then you would need a decent heatsink and power supply for each.
Spending a lot of time around metal halide lamps I really think the best way to go is bounce a majority of the light off the ceiling for a long period while spending a long period of time around the lamp like working on a computer. My mom runs both lights as just one is not bright enough for her liking. I think the sweet spot would be 35,000 – 50,000 lumens for bouncing light off the ceiling in a small room at a close distance for long exposure times. That would be a 315w – 400w metal halide, which you can get them in protected / open housing rated bulbs so you do not have to worry about bulb explosion hazards.
On the Bridgelux LEDs if you drop down to 90 CRI the price comes down considerably and the lumens goes way up. The Vero 29 BXRC-50G10K0-L-24 is 90 CRI, 8800 lumen, 5000K and only $28 from digikey. Using 80W each at 38V you could run four LEDs off a Mean Well LRS-350-36 power supply (~$40) which you can trim to 38V.
I will eventually build a light therapy SAD LED light once the 95+ CRI LEDs come down in price, up in lumens, and hit a higher color temperature. Until then I still think a 315w – 400w protected metal halide is the way to go.
Did you ever build a light? I am considering using one of the COB LED floodlights you describe and mounting it from my 8 foot ceiling and shining directly on myself. I am just not sure how many lumens would be required in this instance. You can now buy one of those fixtures that uses 200 watts and puts out around 20,000 lumens for just over $100, or a 400 watt fixture that puts out around 40,000 lumens for closer to $200. Any thoughts?
I suffer from SAD and have considered building a light box, however, I am more concerned with macular degeneration due to excessive exposure to blue light. I find that 8,000 IU of vitamin D3 per day plus 2mg of melatonin at night is helpful in mitigating both lack of sleep and excessive depression experienced in the late fall – early spring seasons.
My friend evilrooster’s instructable for an SAD LED build in an Altoids tin:
http://www.instructables.com/id/Blue-LED-Light-Box-in-an-Altoids-like-Tin/
Uses LED strips for easy assembly.