LED Lights to replace 'saver' bulbs

[Wond3rboy]

Hi i was thinking of replacing as an experiment the bulb(one of those phillips electricity saving bulbs) in my "Electronics Shack" ( )with an LED light. What i have in idea is to use 8 10mm White LEDs(China) with 80ma current through them(checked their brightness already at this current) from a 1A 5V Supply. I am planning to use them parallely with current limiting resistors. The question i have is should i use PWM using a 555 and transistors(2N222A) for switching the LEDs or just connect the resistors and keep it simple?. If i use the PWM how much should be the frequency for the PWM? I am thinking about 60Hz? easy to do with a 555.

 

[crutschow]

You use PWM only if you want to change the brightness of the LEDS (and you still need resistors). It provides no energy savings over just using a resistor with the DC (unless you add an inductor to perform a switching power supply type function with the PWM)

 

[Wond3rboy]

Hi Carl, . Thanks for your reply. Yeah i will require current limiting resistors in both cases. My question was concering energy conservation and stuff. Guess will do it with some resistors. As far as the inductor is concerned i will first need to get some theory on that since i have'nt done that before. Will stick with the simple thing for now.

 

[Diver300]

LEDs are actually slightly less efficient when you pulse the current through them. The voltage is somewhat higher and the light output per mA is slightly lower at higher currents.

You are better to control the current at a steady value. Boost or buck circuits with an inductor can do that very well.

60 Hz is far too low a frequency. It will flicker horribly. Depending on the duty cycle, 100 Hz flicker can be really distracting or just annoying. I've been able to detect that an LED was being switched at 5 kHz with the naked eye.

If you are using a switched mode current control, the switching frequency will need to be up at 10 kHz or more if you want the inductor to be small.

 

[audioguru]

A compact fluorescent light bulb with a modern electronic ballast (the old ones had a huge and heavy coil inductor) uses less electrical power to make the same amount of light as a bunch of LEDs with current-limiting resistors. Also the CFL bulb shines light all around but the LEDs shine light only in one direction.

The filter capacitor in the CFL bulb will fail in a few years or the fluorescent tube will burn out but LEDs operating at a reasonable current will last for many years.

80mA seems to be too much for a 10mm LED. I looked in Google and found a 10mm white Chinese LED with its max allowed continuous current only 25mA:

 

[Wond3rboy]

Thanks AG. I did a random test and checked whether the LED was getting hot or not. LEDs sold here are done so as open and dont have any ratings. Thanks for giving a specific idea about the current rating. Will see the light intensity at 25ma. I am to place the LEDs in all 4 directions(inclined) as well as pointed downwards. Have shifted to nice 8mm ones, the kind that does not give off a ray of light but a spread out one lke commercial LED lights have.