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Choosing the right white LEDs for my dawn simulator Answered

Hi all!

I'm playing around with a simple DIY dawn simulator alarm clock. I've got a prototype thing working on a breadboard; an ATMEGA88 sends a PWM signal, which fades in a white LED. Adding more LEDs, I thought I'd better send the PWM signal through a mosfet, rather than drive the LEDs directly.

Now I have 5 LEDs, which I grabbed in a pack at the local gadget store. However, looking at LED dawn simulators, it seems I'll need an 6x12 array of LEDs to actually wake someone up. Before I buy bulk online, I was hoping someone might help me choose the right components :)

What I want is,

  • white LEDs
  • I guess large is better? what I have now is 10mm
  • should they be ultra-bright?

Please comment :)


Not positive but I'm not sure you need to care about blue light for your dawn simulator--here's why:

1. Dawn simulation (eyes closed-people sleeping) has been creating pleasant awakenings for years now and all with incandescent light. Incandescents are great because they can be made to light up really slow like a real dawn but they have very little blue. If it's not metal halide (and its not in the commercial products--too expensive? too scary?) there isn't much blue no matter what color they color the glass! Don't think anyone knows why it works but no way can it be the blue light unless VERY VERY little is needed because...

2. Not much blue gets by the closed eyelid! Red passes best. (Ando / Kripke, Robinson)

3. As you hinted at, a real dawn is red, then orange. (Altengarten)

4.The original research is about blue light and melatonin suppression -- the pupils were dilated and the different colors tested with eyes open (at 2am on awake people). This was to test colors for light therapy (treatment with light, eyes open), especially for devising treatments for SAD. (People sad in
winter might have too much melatonin.)
Although it is tempting to think that something similar is going on during awakening, there just isn't much blue light!
Don't think anyone has done any dawn simulation tests with different colors of light. It's always been incandescent (with or without halogen) in the literature. (Terman & Terman, for example)

Not sure why incandescent light (2700K) or a real dawn for that matter (200K-3500K) wakes folks up, but it does.

Other--The commercial dawn simulators using LEDs have an annoying first step of light. (SRS320, Davita) The one I tried woke me up immediately when it blinked on with all if its 5 lux at 40cm at start. May not wake everyone tho'.
==>Maybe you could get rid of the perception of that jump in light by placing a first bank of LED's far away, then bringing up a second bank closer to the sleeper, etc etc.

Or starting with an incandescent source and then lighting the LEDs.

Anyone have a prototype made?


ROBINSON J, BAYLISS SC, FIELDER AR. Transmission of light across the adult and neonatal eyelid in vivo. Department of Ophthalmology, University of Birmingham, U.K. 1991

ANDO Katsuhisa / KRIPKE Daniel F. Light attenuation by the human eyelid, Department of Psychiatry, University of California, San Diego, 1994

ALTENGARTEN Jim. White Balance and Color Temperature in Digital Photography, Apogee Photo Magazine, July 2004

Terman M. et Terman J., J. S. Am J Psychiatry 163:12, December 2006, page 2127

Brainard et al Action Spectrum for Melatonin Regulation in Humane : Evidence for a Novel Circadian Photoreceptor. Journal of Neuroscience? August 2001

Found this at the local gadget-store:

It contains 60 LEDs, which cost me 36cents a piece. And this even comes pre-assembled in a grid, and with a 12V wall wart :-D
I thought I'd simply pulse those LEDs with the PWM, and away we go.

Btw, wrt. blue LEDs: there has been some safety concerns regarding blue light, which apparently has gone unresolved.

Yes, I've looked at those high-power leds... But they're rather expensive and seem to have some tech issues which are, at least for an amateur/hobbyist like me, a little unsettling. They are a little more complicated to drive, right, than normal LEDs, plus they generate a lot of heat. Fire hazard in bedrom? If I were to use normal (5 to 10mm) LEDs, what specifications should I look for, to have a chance of achieving the dawn effect I'm aiming for? Thanks for responding :)

Like, for Mouser, I've narrowed things down to 8 pages :)
Mouser catalog page

I was perhaps thinking to go for 10mm diodes, which yields 3 hits, but then I thought I could do much cheaper with 5mm. Tips, anyone?

go to ebay mouser is usually a rip if it's not for: small capacitors resistors transistors inductors all passive components most semiconductors some connectors

why not a 50 W metal halide beast ? it also fades in slowly on its own without any pwm

I think, your actually building a device to take out hoards of vampires with... Seriously, might be worth adding a mix of Leds, like mostly white, with a few yellows, and a few UV ones.

you can buy some 1 watt LEDs on ebay (I bought 5 for 10 bucks including shipping, I bought them from the US so it's a bit more expensive, but I needed them fast for my project, They are really bright, but you can change that with PWM and/or resistor. 1 watt LED at about 80% brightness, only pictures I'm showing of my new project that should be done really soon, stuff is just drying and I have to touch up stuff.