[sdiy] Alternatives to Faders

[Richard Wentk]

On 8 Mar 2007, at 16:25, Edward King wrote:

> Same question to you then as I just posted to Dave  
> Magnuson....would you be comfortable using a 5 green LEDs, 3 yellow  
> and then 2 red as approximation~?

As I said, the bar graph idea wouldn't be my first choice for an  
interface.

But aside from that - multi-coloured bar graphs have been standard  
issue on equipment since the late 70s, and I've never had any  
problems with them at all.

The eye actually has a very variable sensitivity curve, which peaks  
in green around 530nm, and falls off quite rapidly towards red and  
indigo. The perceived brightness of 650nm red is only about 1/5th of  
that of 530nm green, assuming identical absolute brightness.

This explains why red sometimes looks dimmer. You don't need to be  
colour blind to see this - it's part of the eye's normal response.

To avoid this you may have to match perceived brightness by eye, and  
perhaps optimise the LED current for different colours. So for a  
smooth display, some fine tuning might be required.

But that doesn't sound like an insoluble problem. And as I said,  
people who are *completely* blind to red are really very rare. So I  
wouldn't worry about this too much as an accessibility issue.

Richard