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FAQs > Phos-4 LED Source
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Why is temperature control important ?

The following link describes why temperature control is important when you turn on an LED

Is there a filter slot? If so what size filters are accommodated?

Yes you can include filters in the light path – there is a micro suction pad (P4-FPAD) on the Lens holder that you push the filters on to – there’s no adhesive so it doesn’t leave residue on the filter.
You can use filters that are circular (16 mm, 25 mm diameter) or rectangular (25 x 36 mm)

Can you control intensity?

Yes you can control intensity – the basic way is through the application software – there a video here that demonstrates the use of the software.
Within the software, the Drive tab allows the drive current to each LED drive can be be controlled in 1 mA steps – the maximum current is dependent on the LED type.
The intensity can also be controlled using the pulse width modulation from the PWM tab.  The percent modulation can be set from 1% to 99% in 1% steps; The PWM frequency can be set from 1 Hz to 50 kHz.
The USB and UART interfaces allow more precise control of the Drive current (E.g. current resolution down to 0.3 mA) and PWM settings (frequencies up to 200 kHz)

There is also the option of controlling the current using an external voltage to set or modulate the LED current by connecting the appropriate interface cables (either the P4_ANAS or P4_ANAC).

Is the intensity setting reproducible, so if I run an experiment today can I duplicate that intensity setting tomorrow ?

The intensity setting is very reproducible – The LEDs are temperature clamped to within 0.2°C in continuous mode (settling time <4 minutes at 25°C); the voltage reference used to control the LED current is an 8ppm voltage source.  The result is a stability of up to 0.02% / hour can be achieved.  Note that some optical fibers can result in variations in the measured power, typically ±0.5%.

For multi-die LEDS, how is the light coupled into the fiber?

The Phos-4 P includes a lens in the optical path that can be adjusted in X, Y and Z.  This lens can be used to blend the light in to the fiber as required.
When doing this with multi-die LED modules, its worth de-focusing the coupling in Z, so that the image of the chip on the fiber end is blurred allowing easier blending between the LED dies.
If higher precision blending is required, it can be adjusted with the current setting.  If mode filling of the fiber is a consideration, a diffuser can be added in place of the filter.
Of course there is nothing to stop you from using a multi LEDs as a single LED and maximize the selected die into the fiber.

Can the LED modules be swapped so its easy to change to a new wavelength?

Yes the LED modules are fully interchangeable and are intended to be interchanged by the user. It was a key design feature.
Once the cover is unscrewed, it take a couple of minutes to swap them over.  Its all detailed in the User Manual.

How much power will I get into my fiber optic?

The amount of power coupled into a given fiber optic is dependent on a  number of parameters :- the diameter, the numerical aperture and the type of fiber used.
This table shows typical powers achievable using a Phos-4 P, with a range of single and multi- die LED modules and a range of optical fibres.