# Relationship between illumination and power

Discussion in 'Homework Help' started by roboticvn, Oct 6, 2014.

1. ### roboticvn Thread Starter Member

Jul 9, 2014
47
0
Hi all,
I am studying about visible light communication (VLC). I am wondering follow problems:
1. Relationship between electric power of a LED and its transmitted optical power?
2. Calculating illumination from electric power of a LED?
I hope you help me this problem.
Thank you very much!

2. ### studiot AAC Fanatic!

Nov 9, 2007
5,005
513
To answer these questions you need to study several manufacturers data sheets.

What are your thoughts as to what to look for?

Oct 2, 2009
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4. ### roboticvn Thread Starter Member

Jul 9, 2014
47
0
Thank for your help. I was able to calculate the power from illumination of LED

5. ### roboticvn Thread Starter Member

Jul 9, 2014
47
0
Sorry everyone, but I have a question. Can I calculate center luminous intensity? I read a paper. They have a LED with 20mW transmitted optical power, 70 deg semi-angle at half power and its center luminous intensity is 0.73 cd. The height of LED is 2.5m. I am wondering why they determine LED's center luminous intensity?
Can you help me? Thank you very much!

6. ### studiot AAC Fanatic!

Nov 9, 2007
5,005
513
Well did you consider answering my qustion in post#2?

7. ### roboticvn Thread Starter Member

Jul 9, 2014
47
0
I'm sorry. I have read and I think my problem solved but now I want to establish relationships between illuminance and power. I know the International Organization for Standardization (ISO) in which the illuminance needs to be within a range of 300 lx to 1500 lx for indoor office room. I want to find range of power to reach this condition. Of course, when I had a few parameters such as the height of the LED, angle of incidence,etc.

8. ### studiot AAC Fanatic!

Nov 9, 2007
5,005
513
Is this really homework or would general electronics be more appropriate?

When considering LED lighting you need to consider much more than just the power in and the light levels out.

The system optics (reflector mounting, luminaire height and many other factors) play a big part in a successful LED light.
Also to consider is the polar output curve.

LED luminaires can cause considerable RFI. This should also be taken into account in respect of the intednded location/use.

300 - 1500 lux is a very wide range and office covers a very wide activity description.

I seem to remember Uk standards require a minimum of 50 lux in walkways
and 500 lux where old fashioned drawing office activities take place. (I see it is 750 now)
The measurement is meant to be at desk level.

In a more modern office 1500 lux would obliterate most pc screens.

Here is the CIBSE code

http://www.arca53.dsl.pipex.com/index_files/lightlevel.htm

Evenness of lighting distributuion is also important, as is any daylight available.