Led Pwm

[solis365]

planning a light control unit using high power (1W or 3W) LEDs. planning on PWM for brightness control.

the LEDs are meant for room lighting, which means they could be on for hours at a time, and I was wondering if switching them this rapidly decreased the lifetime or otherwise had a negative effect.

Not sure exactly what frequency i want to PWM at, I read that a few people can detect flicker at 100Hz, so I was thinking 200Hz or 400Hz. It's arbitrary, I have yet to order the components that determine frequency (if i end up using a 555), and the frequency is programmable if I end up using a PIC or other uC.

additionally, what number of these high-power LEDs do people suggest for mimicking the intensity of your average 60-100W incandescent?

thanks!

 

[ronsimpson]

100hz PWM is typical. No life problems.
There is no good correlation between 1 watt LED and light output just like a 100 watt bulb takes 100 watts in, it does not send out 100 watts of light.

 

[solis365]

100hz PWM is typical. No life problems.
There is no good correlation between 1 watt LED and light output just like a 100 watt bulb takes 100 watts in, it does not send out 100 watts of light.

ill probably go with 200Hz... why? because I can and I like being different

and yes they are not 100% efficient but I was wondering if anyone had any previous experience and could say something like "5 high power LEDs at 100% brightness are about a typical lightbulb if diffused by the right shade"... nothing technical, just a rule of thumb to give me an idea.

i plan on an RGB setup as well (also PWModulated) so I have to kind of be careful, i.e. my white light is 3x as bright as my brightest red can be since 3x the LEDs are outputting white as are outputting just red

 

[crutschow]

A 60W incandescent has 850 lumens output and a 100W has 1700 lumens. Divide this by the LED lumens out to get a rough idea of how many you will need. You can convert from candela to lumens, if you need to, using this converter **broken link removed**.

Since an LED is more directional than an incandescent, you may be able to get by with fewer than this calculation would indicate.

 

[ronsimpson]

Are you using RGB LEDs?
Use white LEDs!

 

[davidbball13]

a little off topic.....I just swam in a pool that had RGB leds in the pool and switched colors. i tough the hole swim team how they work. they could careless.

 

[solis365]

im not using RGB LEDs (like, common cathode or something like that).. im using the high power ones, probably luxeons. one each of red, blue, and green for each RGB set that I need.

what are your thoughts on "warming" the light output by adding a few amber LEDs to the mix?

 

[audioguru]

RGB LEDs can make any colour you want by adjusting the brightness of each colour. That is what a colour TV and a computer monitor does.
Amber is red plus green with a little more red than what makes yellow.

White is a lot of blue, less green and a small amount of red.

 

[solis365]

yes, i know, but the idea is to have some separate controls for each setting. rather than warming the light by adjusting the color wheel, i want to keep the color and have a separate dial adjust the warmth, i.e. add specifically to the RG channels. perhaps on the lower end of the "warmer" i could activate some white/blue LEDs to "cool" the light.

the purpose of this project is ambient room lighting. i know its possible to do it by just adjusting the RGB channels, but its harder for the end user to conceptualize color pallette warming and cooling in terms of RGB channel adjustment.

however, now that i have thought about this a bit, i could have a separate warmth slider but not amber LEDs, instead just having the warmth slider feed into the PIC and then have the pic do math to adjust the levels based on the position of the slider.

sorry, sometimes i have to argue against a point to see its merits


still in the design phase so i have a lot of ideas to consider and refine. thats what forums are for, right?