7 Segment Displays and Luminous Intensity

[MrAl]

Hello,


Recently i was looking at some various color 7 segment LED displays
and i noticed they all have a luminous intensity (mcd) rating much lower than
the display i purchased and tested recently.

The one i already bought is red, and it has a rating of 56mcd min, but
the ones i was looking at for possible purchase are only rated one-
tenth of that (about 5.6mcd, or 5600ucd) and some of them are as
low as 1.9mcd. The colors are red, green, yellow, orange, blue,
and white, and so far all of them have low mcd around 6 or lower.

The thing is, 56mcd seems to work out nice with my display circuit
and routine, so what i was wondering is if anyone else has used any
7 segment displays recently that were low on the mcd rating (like 5
or lower) and if so what results they got and what they used to drive
them (how much average current).

Anyone?

Also, anyone ever purchase any of the newer blue displays yet?


Thanks...

[k7elp60]

Hello MrAl,
I have not purchased any of the blue segment displays.

You have an interesting question. I am working on a project that I want to put red LED's in series with white LED's. As you know the forward current in the LED affects the luminous intensity. I connected one red and one white LED of the same MCD and viewing angle in series. Used a current limiting resistor and adjusted the supply voltage until the white was the intensity I wanted. The red was not as visible to me as the white.
In fact the white showed up as a brighter dot than the red.
I am going to try the same thing with a larger (double) MCD rating on the red. If that doesn't work I may have to use independant series strings and vary the current to get equal intensity.

[MrAl]

Hi there Ken,

Oh that's interesting. That suggests that a white color will appear
brighter to the human eye than a red color.

In this case, you can use my comparative intensity measuring instrument
(can be huild at home for almost no cost at all) to compare the white
to the red and determine exactly how much more intense the red appears
than the white, then decide how much more mcd you need for the red.
http://hometown.aol.com/xaxo/page1.html
This simple instrument allows you to calculate the ratio of the intensity
of one light source to another.

Once you do this measurement we can then determine the ratio of
the white to the red and come up with a number that we can multiply
the white by to get a relative intensity for the white that is more
comparative to the red.
For example, say you come up with a factor of 2 like you guessed
already. In this case we would then simply multiply the white by
2, so a 5mcd white would become 10mcd, as compared to red that is.
This would tell me a lot of information because then i could use this
number to estimate how well my display would work if it had white
instead of red LEDs.

Thanks...

[k7elp60]

Hi there Ken,

Oh that's interesting. That suggests that a white color will appear
brighter to the human eye than a red color.

In this case, you can use my comparative intensity measuring instrument
(can be huild at home for almost no cost at all) to compare the white
to the red and determine exactly how much more intense the red appears
than the white, then decide how much more mcd you need for the red.
http://hometown.aol.com/xaxo/page1.html
This simple instrument allows you to calculate the ratio of the intensity
of one light source to another.

Once you do this measurement we can then determine the ratio of
the white to the red and come up with a number that we can multiply
the white by to get a relative intensity for the white that is more
comparative to the red.
For example, say you come up with a factor of 2 like you guessed
already. In this case we would then simply multiply the white by
2, so a 5mcd white would become 10mcd, as compared to red that is.
This would tell me a lot of information because then i could use this
number to estimate how well my display would work if it had white
instead of red LEDs.

Thanks...

Hi Mr Al
Good information,
thanks.