Can someone explain about Lumens?

[Gwylan]

Watts is the electrical energy used to produce the light.

Lumens is the "amount of light" - i.e the radiated energy, weighted according the spectral sensitivity of the human eye. A 100 lumen red light and a 100 lumen green light will look the same brightness, but the former will radiate several times the energy of the latter, because the eye isn't as sensitive to red as it is to green.

Converting watts to lumens depends on both the frequency of the emitted light and on the efficiency of the emitter.
A theoretical 100% efficient light source emitting monochromatic green light at the peak sensitivity of the eye will give 683 lumens per watt.
A 100% efficient light source emitting the various colours that make up white light will give somewhere around 300 lumens per watt.
An old-style tungsten filament light bulb is inefficient because most of the emitted radiation is in the infra-red, which you can't see and hence contributes nothing to the emitted lumens.
The best current LEDs can get up to 200 lumens per watt (though this will be at low power as the efficiency falls as the LED heats up).

The LED light (singular) I'm using in my living room at the moment says on its box: 13.5 W, 1500 lumen, 100W filament bulb eqivalent.

As for what's bright enough for your model photos, you are into the old shutter speed/aperture/ISO trade offs.
Summer daytime sunlight in the UK is about 50,000 lux (lumens per square meter).
The old "sunny 16" rule for photography says that on a sunny day, the shutter speed at f/16 should be the reciprocal of the ISO setting (or film stock), so at ISO 100, 1/100 sec at f/16 is the correct exposure for a sunny day.
So, if you cobble together a 5000 lumen light source and use it to illuminate a 50 cm x 50 cm area of model (with minimal light spill elsewhere), that's 20,000 lux, which would approximate an exposure of 1/100 sec at f/16 using ISO 250. Alternatively, the same light source illuminating 1 sq m will give 5000 lux, needing ISO 1000 for the same shutter speed & aperture.

These are ballpark numbers. In the real world you can reckon on losing at least half the 5000 lumens to light absorbed in the light fitting, or falling outside the desired area of the model.

Lumens are what the light source produced. Integrated over the entire spher of the source.
Lux is the amount of light arriving on the illuminated surface.
That depends on the efficiency of whatever optical system is being employed.
The inverse square law applies
The spectral power distribution of the light source should be taken into account.

Most of the data produced by the riffraff on the interweb is total bollocks, even lies or irrelevant
That brings one to the claimed wattage equivalent, that is the last refuge of these scroats

 

[Dadam]

Modern cinematographers pay lots of attention to colour and will even have a colour palette they work from. This is very visible in the current Nordic Noir style of drama on TV

And, unfortunately, most historical TV and movies set in mediaeval periods. Everything shot with a blue filter so it looks bleak and grim. And everyone wearing drab brown cloth or black/brown leather tunics. Grrr! They loved bright colours!

 

[CXRAndy]

Because of the various light emitting devices, using power(Watts) is not linear. Led light could produce far more lumens than an incandescent bulb for far less Watts.

Just use the lumens figure for intensity and Kelvin for colour of light

 

[Gwylan]

And, unfortunately, most historical TV and movies set in mediaeval periods. Everything shot with a blue filter so it looks bleak and grim. And everyone wearing drab brown cloth or black/brown leather tunics. Grrr! They loved bright colours!

That's because HD shows everything and it's cheaper if you shoot in semi darkness and blame the plot setting.

 

[Gwylan]

Because of the various light emitting devices, using power(Watts) is not linear. Led light could produce far more lumens than an incandescent bulb for far less Watts.

Just use the lumens figure for intensity and Kelvin for colour of light

Oh dear me.
The Kelvin figure for most light sources is an act of fantasy
Kelvin figures are for the colour temperature radiated from a linear source. LED are not linear radiating sources and most of the published data is tosh.
Kelvin colour temperatures are based in a tungsten filament source. Did I mention that?

 

[Yellow Saddle]

Oh dear me.
The Kelvin figure for most light sources is an act of fantasy
Kelvin figures are for the colour temperature radiated from a linear source. LED are not linear radiating sources and most of the published data is tosh.
Kelvin colour temperatures are based in a tungsten filament source. Did I mention that?

OK, I don't understand. What units should we then use for expressing the colour of a LED source and how would that differ from a tungsten filament. I understand that the temperature of the LED is not, 8000K, for instance, but the colour is still the same.
I also don't understand what linearity has to do with it.

 

[Scaleyback]

Paging @Scaleyback of Little People fame.

I'm flattered by you directing this question toward me. 🤗 Unfortunately I am a product of the ' dark ages ' ( pun intended ) and am still a paid up member of the candle power generation. 🤪

 

[presta]

OK, I don't understand. What units should we then use for expressing the colour of a LED source and how would that differ from a tungsten filament. I understand that the temperature of the LED is not, 8000K, for instance, but the colour is still the same.
I also don't understand what linearity has to do with it.

I think he means that colour temperature is a single dimensional scale that attempts to define a two dimensional space. It's reasonably convenient for tungsten because the light's generated by heat, and so the range of colours produced is confined to just those that are directly related to the temperature of black body radiation, but that's not the case for LEDs.

 

[MontyVeda]

just experiment with various lights, torches, lamps and diffusers (kitchen roll, tracing paper, tissue, etc.). I'm sure you'll be able to concoct something with what you've got.

 

[classic33]

I'm flattered by you directing this question toward me. 🤗 Unfortunately I am a product of the ' dark ages ' ( pun intended ) and am still a paid up member of the candle power generation. 🤪

But you have taken similar pictures to what is wanted, in your Small People threads.
I was thinking more of the setup used by yourself to avoid shadows.

 

[Scaleyback]

But you have taken similar pictures to what is wanted, in your Small People threads.
I was thinking more of the setup used by yourself to avoid shadows.

I used a Light tent for those photo's, ( See posts here: ) over head LED lighting to avoid shadows.

I paid £62.00 for my Light tent, that was in 2020. The led overhead lighting is adjustable by a dimmer switch arrangement. Hope that helps ?

P.S If you want to vary the position of the model or indeed take videos a rotating ' cake ' etc turntable allows you move subjects position without handling. You can get remote control powered ones. Are you intending to 'hand hold' your camera phone ? A camera stand would probably be advisable. Best of luck.