Light bulbs - CFL versus LED

[Fluorescence]

Hi,

I am thinking about how to do a light bulb (~10W) with LEDs.....

http://www.lightbulbs-direct.com/product/1007/gls-40w-bc-pearl/

Being offline, the SMPS would need to go in the base, where it would be unventilated and very hot since its above the bulb itself.

The heat is thus the biggest problem.

Since electrolytic caps are the most heat sensitive components that will be used, it is essential to keep the number (size) of electrolytics down.

As such, considering the heat, and the need to keep few electrolytics, it is easier/better/cheaper to do an SMPS converter for a CFL than for a LED bulb....

This is because the CFL does not need smooth DC for operation.....but just requires rectification, one small electrolytic to smooth the DC bus, then two transistors to switch this into a transformer, the output going straight to the fluorescent lamp. -just one electrolytic on the DC input bus is used.

It would be impossible to do a LED lamp of similar wattage using so few electrolytics ?

Have i found the reason why LED light bulbs will never compete with CFL's ?

 

[MacGyverS2000]

Have i found the reason why LED light bulbs will never compete with CFL's ?

No, and we've pretty much passed the point at which you can make that claim (without bringing cost into the equation).

Lumen for lumen, the LED bulb is now going to be more efficient than the CFL, which means the SMPS will have to endure less heat in an LED bulb. Quality CFL supplies are available, just not on the dollar-store 4 pack most people purchase. Copy the good designs and be done with it.

Also, considering the multi-Watt LEDs typically run at 350mA to 1A, you don't really need a humongous cap. String a few low-current LEDs in series for a reasonable voltage (10-20V) and enjoy life.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[VEBill]

Not exactly the same, but...

http://www.ledshoppe.com/Product/hou/HE1040.htm

http://www.ledshoppe.com/Product/hou/HE1035.htm

 

[itsmoked]

LOL! VE1BLL; I bought one that was similar to your second example about 6 years ago. It cost me over three hundred dollars! It was pathetic too. However it used so little power that the SSR's built-in snubber 'leaked' enough power to light it to about 90%. So whenever the SSR went OFF the lamp dimmed only perceptibly.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Fluorescence]

Thankyou all for the replies,

Most LEDs seem to be rated for 50,000 hours, though Electrolytics are only rated to stay good for ~2000 hours.

So do you believe that it's best to put in enough electrolytics such that each electrolytic will only experience <50% of its rated ripple current ?

..i am making the presumption that since the 2000 hours life is for when it experiences its rated ripple curent, decreasing the ripple current each cap experiences will improve life time of the electrolytics and hence the product.

eg this electrolytic datasheet says the 2000 hour life is for when it has rated WV on it......

http://www.platan.ru/pdf/datasheets/jamicon/TK.pdf

 

[itsmoked]

While LEDs are rated at 50,000 hours they reduce in brightness substantially over that time.

You need to read up on aluminum electrolytic capacitors. The hours you are stating refer to hours at the maximum rated temperature, NOT at the temperature a proper design would be running at. Figure out a rational temperature your cap and electronics should be operating at and then look at the cap's life. It approximately doubles for every 10 degrees less then the caps rated life temp.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[MacGyverS2000]

The 50k hours quoted for many LEDs is the point at which they will emit 70% of their original brightness, assuming the die is kept at 25C (or whatever the datasheet specs it at). If you underpower the LED and keep ambient heat under control, your house will probably collapse around you before the LED starts to dim.


Dan - Owner

http://www.Hi-TecDesigns.com