cool/warm white LEDs

[Graham_Wright]

Cool white leds are cheap as chips and abundant. (Just received 10 off 24 smd arrays with back pins, £5.69 post free.) Warm white are less so.

Is it possible to filter cool to make warmer?

 

[johnalison]

It must be possible since white light is always a mixture of at least 3 colours but whether the loss of brightness is acceptable is a different matter.

 

[AngusMcDoon]

Cool white leds are cheap as chips and abundant. (Just received 10 off 24 smd arrays with back pins, £5.69 post free.) Warm white are less so.

Is it possible to filter cool to make warmer?

You could add some yellows and reds.

 

[Graham_Wright]

You could add some yellows and reds.

SMDs are after my time! Not sure I could cope!

 

[charles_reed]

Cool white leds are cheap as chips and abundant. (Just received 10 off 24 smd arrays with back pins, £5.69 post free.) Warm white are less so.

Is it possible to filter cool to make warmer?

You may be missing a basic point - LEDs are very efficient at producing high frequency (ie blue) light, mixing in longer frequencies to produce warm white involves "doping" the LEDs and dramatically reducing light output. Warm white LEDs need to be 150-250% more powerful than their cool white brethren to produce the same light output, hence the price difference. In fact, for 2600K light, LEDs are less efficient than discharge tubes.
The idea of mixing in some of the other spectrum colours is interesting - perhaps someone may be prepared to hazard a guess as to why it's not done commercially.

 

[Graham_Wright]

You may be missing a basic point - LEDs are very efficient at producing high frequency (ie blue) light, mixing in longer frequencies to produce warm white involves "doping" the LEDs and dramatically reducing light output. Warm white LEDs need to be 150-250% more powerful than their cool white brethren to produce the same light output, hence the price difference. In fact, for 2600K light, LEDs are less efficient than discharge tubes.
The idea of mixing in some of the other spectrum colours is interesting - perhaps someone may be prepared to hazard a guess as to why it's not done commercially.

I bought one of these intending to fit six in a sexy arc across the "stateroom" deck head - G4 24SMD 5050 12v (10-30v) DC 4.2W Back Pin Cool White LED Light Bulb.

It was so bright as to be painful. I guess I could cope with a little attenuation!

 

[nigelmercier]

Is it possible to filter cool to make warmer?

Or leave them as they are. Once you are used to it, you won't want to go back.

 

[rotrax]

We have mostly warm white for ambiance, cool white for reading-a good compromise.

 

[nimbusgb]

No, 'filtering' will not warm up a cool white LED, the emission bandwidth is already so narrow all you will do is make it dimmer. Far easier to acheive by lowering the drive current!

Some commercially available 'white' leds have a cool white emitter alongside a yellow emitter to spread the light spectrum to cool it down a bit.

 

[pteron]

The idea of mixing in some of the other spectrum colours is interesting - perhaps someone may be prepared to hazard a guess as to why it's not done commercially.

The problem is that the additional colours you could add are very narrow bandwidth and whilst it looks like you have a warmer white coming out, the actual colour gamut is poor. Nevertheless, some bulbs do add a bit of red or amber but it is expensive to do so as the drive requirements for a red LED are different to those for a white LED, so separate circuitry is needed.

 

[Graham_Wright]

No, 'filtering' will not warm up a cool white LED, the emission bandwidth is already so narrow all you will do is make it dimmer. Far easier to acheive by lowering the drive current!

I though white light was wide bandwidth?

 

[pteron]

I though white light was wide bandwidth?

It can be, but isn't necessarily.

There needs to be components of red, green and blue in it to fool the eye into seeing white but it doesn't have to be wide band.

 

[nigelmercier]

I though white light was wide bandwidth?

Not from LEDs it isn't.

White LEDs are essentially UV LEDs with a fluorescent coating in the internal structure. Expect a similar light to a fluorescent tube, peaks throughout the spectrum.

 

[Graham_Wright]

I tried a piece of red plastic (probably perspex) for the low level night lighting and it worked a treat so there must be a bit of the red spectrum left?

 

[nigelmercier]

I tried a piece of red plastic (probably perspex) for the low level night lighting and it worked a treat so there must be a bit of the red spectrum left?

I've just looked this up, and the spectrum is less "peaky" than I thought:

 

[Graham_Wright]

I've just looked this up, and the spectrum is less "peaky" than I thought:

……and with red in the band 620-750, not a lot is going to get through! (But yellow might have a chance).