Calculating Lux for Lamps

I found some equations here:

http://www.ndlight.com.au/lighting_calculations.htm

However, you might be better served with a hand-held meter:

http://www.mcmconnect.com/tenma/product/72-6693/

Just an example, there are many on the market.

Why does this question come up about every two weeks? Is this a homework question?

Don't calculate it. Measure it.

I was caught by these type calculations in another job (so long ago, it seems like another life). Seems there is a perception by managers that electrical engineers should all have been taught everything there is to know about lighting, since artificial sources usually do involve electricity. However, many EE's have never been exposed to this concept, especially if they took primarily semi conductor courses. I was asked to calculate lighting levels and fixture placements in buildings and parking lots right out of college. Not being one to disappoint, I got books (no Google or CR4 in those days) and taught myself. I suspect such assumptions by managers are still being made today - thus a persistent question on this site, since a quick answer is available.

By the way - that first job sent me back to school for a good dose of physics to compliment the EE degree.

you can calculate as follow,

1 Lux = 1 Lm / M²

there will be 4pi Lm on surface of 1M redius sphere fo r 1 Cd intensity.

how many cd is your lamp, so that you can get x cd* 4pi =lm

the sphere surface is 4pi * radius², so that the Lux = x cd * 4pi/ 4pi * radius²

we get, Lux = x cd / radius^{2 .} do attation, this is sphere surface. if you hope to calculate on plate (plan), you have to use geometry method to transform.

hoever a software is convinient at the time, if you hope to do a lighting project.

Ya cn, it comes up often, and is almost always misunderstood. You don't actually measure the lux of a light source. That source could be the sun or a small flashlight. Lux is the measurement... Oh darn, they can read about it themselves here:

http://en.wikipedia.org/wiki/Lux

Hi, Bricktop,

I read the link you refer to. This explain is vague and can comfused people. I shall amend that item.

Lux has to be calculated before a lighting project. its not simple sometimes. with help of software, it will become easy.

measure is another thing when you complete the project. or change while in engineering.

once you do the job, you will know why peopple have to calcucate it.

Regards

You can directly measure the intensity of light using a lux meter. Came across a good model.

http://www.industrialindia.com/catalogs/Digital_Portable_Lux_Meter/Digital-Lux-Meter-HTC-LX104.pdf

Hi Guest,

I am interested in the type, colour and intensity of light, having been and hopefully will take up amateur photography?

I appreciate your site address, thanks.

Take care

Hello bsnathan,

'Watts' is the power used to to give a light. But the same watts can be used with different lamps, and give 'more' or can give 'less' 'lux', depending on the bulb you chose.

As a general rule you can get more light or Lux from the newer 12 volts halogen types of lighting, for a given amount of power.

"Incandescent' lamps, the normal 'cheap' type lamps give out a yellow light which some think is 'warmer'.

You will need more power to get what is 'apparently' the same amount of light from incandescent bulbs. I say apparently as people cannot always realise the yellow light of incandescent bulbs.

Where 'Halogen' give out a very white light. Some think this is 'colder' than the old yellow light of incandescent bulbs.

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Explanation

Lux is a derived unit based on lumen, and lumen is a derived unit based on candela.

One lux is equal to one lumen per square metre, where 4π lumens is the total luminous flux of a light source of one candela of luminous intensity:

1 lx = 1 lm·m-2 = 1 cd·sr·m–2.

As with other SI units, SI prefixes can be used, for example a kilolux (klx) is 1,000 lux.

Illuminance Example

10-5 lux Light from Sirius, the brightest star in the night sky[2]

10-4 lux Total starlight, overcast sky[2]

0.002 lux Moonless clear night sky with airglow[2]

0.01 lux Quarter moon

0.2 lux Design minimum for emergency lighting (AS2293).

0.27 lux Full moon on a clear night[2][3]

1 lux Full moon overhead at tropical latitudes[4]

3.4 lux Dark limit of civil twilight under a clear sky[5]

50 lux Family living room[6]

80 lux Hallway/toilet[7]

100 lux Very dark overcast day[2]

320 lux Recommended office lighting (Australia)[8]

400 lux Sunrise or sunset on a clear day. Well-lit office area.

500 lux Lighting level for an office according to the European law UNI EN12464.

1,000 lux Overcast day[2]; typical TV studio lighting

10,000–25,000 lux Full daylight (not direct sun)[2]

32,000–130,000 lux Direct sunlight Unicode has a symbol for "lx": (㏓), but this is just a legacy code to accommodate old code pages in certain Asian languages, and it is not recommended for use in any language today.

Lux versus lumen

The difference between the lux and the lumen is that the lux takes into account the area over which the luminous flux is spread. A flux of 1,000 lumens, concentrated into an area of one square metre, lights up that square metre with an illuminance of 1,000 lux. However, the same 1,000 lumens, spread out over ten square metres, produces a dimmer illuminance of only 100 lux.

Achieving an illuminance of 500 lux might be possible in a home kitchen with a single fluorescent light fixture with an output of 12,000 lumens. To light a factory floor with dozens of times the area of the kitchen would require dozens of such fixtures. Thus, lighting a larger area to the same level of lux requires a greater number of lumens.

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The piece above will give you some idea of the light given out by a lux.

Good luck.

You can directly measure the intensity of light using a lux meter. Came across a good model.

http://www.industrialindia.com/catalogs/Digital_Portable_Lux_Meter/Digital-Lux-Meter-HTC-LX104.pdf

I like this question ...I looks just like one from a Homework sheet I had about two (2) months ago...

I found the answer in a Text book.... A strange device made of Flat Trees.. with funny symbols on it.

Regards,

Sapper

Hello TVP45:

are you OK?.........At the moment I am giving the OP a little slack.

Allowing for him being busy, on holiday etc. BUT.............IT WOULD BE NICE FOR PEOPLE WHO HAVE HAD HELP TO HAVE THE COURTESY TO REPLY.

And, that was good and simple advice TP45. Wonder why OP did not think of it, mmmmm

Take care............

Thanks,

Another way, if you have a spotlight or reflector of known angle, is to specify the lux for a certain circle diameter.

Hello zub_kci, some of these site offer calculator to work out the lux. Others show Formulae. Hope you find what you are looking for. Please forgive any duplication if other posts have the same sites. I have not read any of the thread yet. http://www.ndlight.com.au/lighting_calculations.htm

http://www.voltimum.co.uk/find/page-11-10-2/collec-vltsearch/how-to-calculate-the-lux-level.html

http://www.lightsearch.com/resources/lightguides/formulas.html

http://www.flg.co.uk/data_lighting_design_request/data_lighting_design_req.html

This site has a calculator to work out the Lux www.flg.co.uk/data_lighting_design_request/data_lighting_design_req.html

www.lightsearch.com/resources/lightguides/formulas.html

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