LED lights efficincy

[Orionaut]

Just a quick question.

An LED typically operates at less than 1 volt DC.

Mains is 240Vac.

How much of the power used by an LED light bulb is used by the LED/LED array (Series/parallel) itself to produce useful light, And how much is "Wasted" in the power supply/driver that converts the mains supply voltage and feeds it?

 

[Doobedoo]

Not all led lights will be equal but I’d imagine you’d first need to know how many lumens per watt is outputted and then how many watts it would consume, I suppose you could also measure lumens outputted.

This may be of interest to you https://www.dial.de/en/blog/article/efficiency-of-ledsthe-highest-luminous-efficacy-of-a-white-led/

In addition, the overview shows energy conversion efficiency of the lamps examined. The energy conversion efficiency describes how much of the power is converted into visible light. In this respect efficient LEDs are clearly well ahead of conventional lamps. While energy conversion efficiency of incandescent lamps, for example, is between 10% and 20%, very efficient LEDs at present achieve values between 40% and 50%. Nevertheless, this is still »only« 40 – 50%, so 50% to 60% of the power is »lost« as heat.

 

[Orionaut]

Not all led lights will be equal but I’d imagine you’d first need to know how many lumens per watt is outputted and then how many watts it would consume, I suppose you could also measure lumens outputted.

This may be of interest to you https://www.dial.de/en/blog/article/efficiency-of-ledsthe-highest-luminous-efficacy-of-a-white-led/

Not saying that LEDs are not a lot more efficient than alternatives (Though they do have other issues of concern, low light level UV is my main one)

Just wondering how much room for improvement exists in the power supplies.

Bearing in mind how hot the "Bases" get, I am expecting that although the lumens/watt overall is good.

"Most" of the power will be being consumed by inefficiencies in the LED driver circuits rather than the in LED's themselves.

 

[Doobedoo]

Look at my post again. It states that between 50-60% is lost as heat.

I’d imagine the manufacturers have or are currently looking at power supply efficiency increases but as the power draw is already low I doubt there would be much of an improvement.

There is no question that the LED is an efficient light source. Nevertheless, even the LED is subject to physical limits when it comes to luminous efficacy. The theoretical maximum luminous efficacy always depends on the desired spectrum. Big advances cannot be expected nowadays.

Claims such as »In a few years white LEDs will achieve a luminous efficacy of 500 lm/W!« are quite simply wrong because this is physically just not possible.

 

[LuckyBenski]

The question doesn't necessarily make sense. Efficiency is defined as useful power out (so, light) divided by total power used. Anything less than 100%, then the remainder is heat. Light bulbs emit no or negligible sound or motion energy.

So their improved efficiency IS the lumens per watt, and it's better than CFLs which were better than incandescents.

I do question how hot they get as well - but remember, there is basically no heat coming off of the actual bulb itself. Even CFLs get a little warm. So the exact same heat output as a CFL in the circuitry, would still be better overall.

"Most" of the power will be being consumed by inefficiencies in the LED driver circuits rather than the in LED's themselves.

"Most of" maybe, but then that proportion was mental in incandescents. "Most of" the energy used in those was wasted as heat - something like 90%!

 

[R.C.Anderson]

First thing you need to consider, is that although a single LED has a very low voltage, very few (I doubt any, but I haven't checked them all) only actually have 1 LED. Normally it's an array of chips (depending on the number, it might be a mixture of series & parallel connections), which would increase the required voltage.

In order to drive at the correct DC voltage, a voltage converter is used. There's a few options to provide this (I'm going to very simply touch on each point, for more in depth details, you're best doing a bit of googling on the main points):
- Transformer to reduce the AC voltage, then rectify to DC - transformers are big, heavy & expensive. They use the magnetic field generated by an incoming AC current to generate a current in an output. By using a different number of coils of wire on the input & output of the transformer allows the voltage to be increased or decreased. - This option is very rarely used in modern LED lights.
- Rectify to DC, then use a Linear voltage regulator to reduce the voltage - The least efficient, so not used for large loads or large voltage changes. Essentially, this drops the voltage by causing a volt drop over the regulator (these get hot, as they're very inefficient & "waste" is dissipated as heat). If this was used, using a 100V supply, a 1V load would be 1% efficient, a 50V load would be 50% etc (assuming all elements to be 100% efficient).
- Rectify to DC, then use a switched voltage regulator - These are generally quite efficient. They switch the incoming supply voltage to give an "average" voltage of what's required, which is smoothed to provide a constant voltage at the level required.

I'm not sure of the actual % of how efficient an LED light is, but from memory, they're in the "several 10s" of % efficient (which is a huge bonus over the <10% of incandescent & <20% of CFLs).