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You can get a plastic DSLR camera body cap for less than 50 cents each (ebay from China). This cap goes where the lens would attach the camera when you don't ha
by danielvf 8y ago
You can get a plastic DSLR camera body cap for less than 50 cents each (ebay from China). This cap goes where the lens would attach the camera when you don't have a lens on. Sometimes I cut a hole in the center of a cap and make really hacky camera "lenses" for fun. You could put a prism on the outside of a cap.
You would then need to calibrate your new spectra-cam on something with a known radiation (usually just find a good blackbody radiator.) You can't just convert to black and white without calibration because the RGB sensors on the camera are going to have their own sensitivity to different wavelengths. This would be an awesome project!
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I write firmware for high end professional LED lights, and have a $3K spectrometer on my desk. Here are things I've learned:
1. CRI is simply a bad formula to judge light quality overall and gives almost meaningless results at lower color temperature levels.
2. There are lots of fantastic python modules for working with spectrograph and light data.
3. One awful thing cheap LED lights do is blink slowly to control their voltage. This is at least as bad a poor CRI for aggravating your eyes. (Sometimes you can see this just by using slow motion video on your phone)
- tomcam 8y agoSorry for the off-topic reply, but it’s people like you that make HN awesome
- tyingq 8y agoInteresting detail. On this, though: >One awful thing cheap LED lights do is blink slowly to control their voltage I assume you're talking about PWM. That's not just to be cheap. It's the only real way to control brightness.
- deleted 8y ago[deleted]
- danielvf 8y ago(Sorry, I meant to say that I hate cheap LED lights that blink slowly to control their brightness.) Blinking the LED on/off to control its brightness with a PWM is definitely not the only way to control output. And if you are controlling by blinking, PWM is still the bottom of the pile in ways to blink, from a quality of light point of view.
- CamperBob2 8y agoWhat other ways are there? Nobody is going to want to dissipate heat in a linear element somewhere, are they? I guess that because LEDs are actually so efficient, that isn't such a bad idea as it sounds at first.
- smaddox 8y agoPWM could be combined with a capacitor in order to smooth the voltage out. Or sufficiently high PWM frequency can be used (10s of khz), in order to avoid eye strain. The former approach might negatively affect the efficiency, though, depending on where the efficiency peak is.
- jononor 8y agoA constant current source does not have to be linear, one can use a switchmode powersupply with current regulation. Then the current though the LED flows in a continuous manner.
- solarkraft 8y agoSwitch-mode regulators don't pulse? How wrong am I to think that a capacitor after the PWM-regulator would give a reasonably good approximation of a constant voltage?
- jononor 8y agoSure they pulse/switch, but that is into/from the inductor/capacitor used as intermediate energy storage, not through the load (LED). At the output a constant voltage is seen (plus some ripple). A capacitor on PWM output will give a decent approximation, _if_ it is big enough. For large LEDs this can be very costly (relative to other parts in system). Though the inductor in a switching converter is also a big cost driver. Both for the capacitor, inductor and wrt to human perception increasing switching frequency helps. So that is what modern designs focus on normally. A challenging aspect of LEDs is their nonlinear voltage versus current characteristic. A small change in voltage gives a very large change in current, and thus in output power. The characteristic is temperature dependent and has per device variation. Hence LED drivers are usually constant-current sources, ie they measure and attempt to regulate the current.
- psandersen 8y agoLight quality has been something I've been interested in for a while so I've invested in making my whole environment use LIFX and Yeelight bulbs. This has been great and I get bright neutral lighting during the day, warmer light in the evening and variations of colour gradients and themes when friends are over to chill. However, I have no way of knowing if something is missing from the light quality or how I'd even go about optimising things both for my health/comfort and for indoor plants. Does anyone have recommendations?