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  4. Efficiency of light as energy source?
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Efficiency of light as energy source?

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Offline scientizscht (OP)

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Efficiency of light as energy source?
« on: 21/06/2018 15:42:24 »
Hello!

What is the optimum lux to maximise conversion of light into energy? What is the efficiency of this conversion?

Thanks!
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Offline Bored chemist

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Re: Efficiency of light as energy source?
« Reply #1 on: 21/06/2018 20:26:04 »
Light already is energy.
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Online evan_au

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Re: Efficiency of light as energy source?
« Reply #2 on: 21/06/2018 22:56:54 »
Quote
maximise conversion of light into energy?
What sort of energy do you want to convert it into?
- If you want to convert it into light, an ordinary mirror will do that with over 50% efficiency (and an astronomical mirror will do it with over 99% efficiency)
- If you just want heat, any black surface will do. Covering it with a sheet of glass will reduce the amount of heat lost by convection and re-radiation.
- If you want electricity, cheap solar cells will give about 10% efficiency, while space-rated ones might give you over 20%. In this case, you have to allow air to circulate to keep them cool, as they lose electrical efficiency when they get hot.
- Commercially, both thermal and electric systems are optimised for sunlight, with about 700W per square meter
- In theory, they would both continue to work (a bit) under a full Moon, at about 0.01 Watts per square meter, so it would be a challenge to measure it!
See: http://forum.solar-electric.com/discussion/22560/full-moon-wattage
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Offline scientizscht (OP)

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Re: Efficiency of light as energy source?
« Reply #3 on: 22/06/2018 00:00:50 »
Quote from: Bored chemist on 21/06/2018 20:26:04
Light already is energy.

Not very useful as electricity.
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Offline PmbPhy

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Re: Efficiency of light as energy source?
« Reply #4 on: 22/06/2018 10:02:07 »
Quote from: scientizscht on 22/06/2018 00:00:50
Quote from: Bored chemist on 21/06/2018 20:26:04
Light already is energy.

Not very useful as electricity.

Light isn't energy. It has energy. Big difference.
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Offline scientizscht (OP)

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Re: Efficiency of light as energy source?
« Reply #5 on: 22/06/2018 14:33:04 »
Quote from: PmbPhy on 22/06/2018 10:02:07
Quote from: scientizscht on 22/06/2018 00:00:50
Quote from: Bored chemist on 21/06/2018 20:26:04
Light already is energy.

Not very useful as electricity.

Light isn't energy. It has energy. Big difference.

Well said.
But what about some figures for my question please?
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Offline Bored chemist

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Re: Efficiency of light as energy source?
« Reply #6 on: 22/06/2018 18:16:40 »
Quote from: scientizscht on 22/06/2018 00:00:50
Quote from: Bored chemist on 21/06/2018 20:26:04
Light already is energy.

Not very useful as electricity.
True, but very handy if you want to see where you are going.
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Offline Bored chemist

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Re: Efficiency of light as energy source?
« Reply #7 on: 22/06/2018 18:19:40 »
Quote from: PmbPhy on 22/06/2018 10:02:07
Quote from: scientizscht on 22/06/2018 00:00:50
Quote from: Bored chemist on 21/06/2018 20:26:04
Light already is energy.

Not very useful as electricity.

Light isn't energy.

Unless, of course, it is.
http://www.bbc.co.uk/schools/gcsebitesize/science/aqa_pre_2011/energy/heatrev4.shtml
What do you think it is; chicken soup?

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Re: Efficiency of light as energy source?
« Reply #8 on: 22/06/2018 18:52:27 »
Quote from: Bored chemist on 22/06/2018 18:19:40
Quote from: PmbPhy on 22/06/2018 10:02:07
Quote from: scientizscht on 22/06/2018 00:00:50
Quote from: Bored chemist on 21/06/2018 20:26:04
Light already is energy.

Not very useful as electricity.

Light isn't energy.

Unless, of course, it is.
http://www.bbc.co.uk/schools/gcsebitesize/science/aqa_pre_2011/energy/heatrev4.shtml
What do you think it is; chicken soup?

It's like saying electrons are energy, when in fact their movement is.
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Offline jeffreyH

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Re: Efficiency of light as energy source?
« Reply #9 on: 22/06/2018 19:17:35 »
Photons are defined in terms of energy, E = hf. Here h is Planck's constant and f is the frequency of light. Since frequency is variable then any equivalent mass that can be defined for the photon also changes. This cannot be defined as rest mass and therefore must depend entirely upon kinetic energy. In terms of objects with rest mass, kinetic energy is connected to a change in velocity and not to any change in frequency. The energy changes for entirely different reasons. This is like comparing apples and pears.
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