Latest Thinking About LED Lamps

[bernardgreen]

A trial is being conducted at a friends house where his 12 volt LED lamps are being supplied from an 11 volt supply.

Do I take it that these are 'cheaply made' LEDs without a 'proper' constant-current supply to the LED elements?

They were not cheap to buy but could have been cheap to manufacture in terms of component costs.

From memory I recall they had a three pin voltage regulator and resistor configured a constant current source. This IC and two LED elements mounted on a heat sink.

The LEDs would hav been circa 3 volts so 6 volts in them. 3.3 volts across the resistor leaving 2.7 ( approx ) across the voltage regulator ( input to output ) which would be dissipating 2.7 x I watts ( I = current through LEDs )

Hence taking the supply down to 11 volts would reduce the heat dissipated from the regulator ( assuming the regulator worked with a 1.7 volt drop across it. ) but the heat from resistor and LEDs would be the same.

 

[securespark]

Oooh, I love it when you talk dirty!!

 

[securespark]

As to looking at the lamp in my living room 10 lamps 9 are 3W and one is 1.4W I have asked many a visitor to identify the 1.4W and in the main they fail. I also swapped a tube 5100 lumen to 2400 lumen again could not notice it being any dimmer. However have noticed I need to ware my glasses more to read things. I think our brain associates colour with brightness and we think if reddish it's dim and blueish it's bright and since dimming a LED does not change colour we don't see it as being dimmer.

I hope that's not the case!!

I want to fit these lamps to make the room brighter!

 

[bernardgreen]

Eric is right, the brain's "measurement" of brightness is affected by the colour of the light. And add to that the eye's aparture being opened in dim light to compensate for the dimmer light and it is easy to see ( pun not intended ) that estimating brightness by eye alone doesn't give reliable or accurate results.

 

[JBR]

I understood that the colour our eyes are most sensitive to is green or green-yellow.

 

[lloyda]

Look up "Long Life Lamp Co" on Amazon. I have 40 of the 6w warm white throughout my house (not my choice, I had to replace 40(!) 50W halogens when I moved in!

Are these the 120 degree beam ones that are currently being advertised? For what is usually a spot, seems a very large beam angle. I guess this is why the surface of the lamp is not flat.

 

[JohnW2]

... estimating brightness by eye alone doesn't give reliable or accurate results.

In scientific/engineering terms, that's true - but, given the purpose of lighting, it's surely the eyes' perception of brightness which actually matters, regardless of what "reliable and accurate" measurements might say?

Kind Regards, John

 

[securespark]

Have fitted the 10W GU10 LED lamps.

The light looks very different as they are warm white not cool white as before. But the increase in light output is incredible, even when I just had 1 fitted.

As you say John, my eyes perceive a great increase in light output!

Now all 8 are in, it's fantastic. 680 lm each now - the old ones were 320 lm.

And it's still only a total of 80W load!

 

[JohnW2]

From memory I recall they had a three pin voltage regulator and resistor configured a constant current source. This IC and two LED elements mounted on a heat sink. ... Hence taking the supply down to 11 volts would reduce the heat dissipated from the regulator ( assuming the regulator worked with a 1.7 volt drop across it. ) but the heat from resistor and LEDs would be the same.

If the LEDs were mounted on the same heat sink as the regulator, then I suppose the reduced heat from the regulator might have some impact on LED life - but given that the same amount of heat would be generated within the LED itself, I don't think that my expectations would be all that high!

In any event, as I said, particularly if one is not 'young', I'm not sure that one needs to be too concerned about extending LED life beyond what they are claimed to have 'at specified voltage' (many years, at 'a few hours per day')

Kind Regards, John