Frezzi Energy Systems
February 23, 2010
Document Name: Full Spectrum light sources compared with LED fi
When using a LED light source for video or film production in daylight, foot-candle output of present fixtures may not be strong enough to fill in facial shadows while shooting in broad daylight. Video and film pro’s have traditionally relied upon HMI’s (Discharge Sources), bounce cards, and even tungsten halogen for this purpose. However, for interior or night shooting, LED sources are being employed for run and gun and other uses with mixed success.

Every light source emits electromagnetic energy and the most effective way to measure and judge the quality of the light source is by spectrophotometry. Fig. A shows a spectrograph of a Frezzi 50 Watt Mini-Fill using a GE MR-16 bulb.
MiniFill Tungsten Spectrum.jpg
Fig. A
tungsten halogen
Fig. B
White LED SpectrumNEW.jpg
Fig. C
As you can see the spectrum is continuous with no gaps in the visible spectrum. In this respect the spectrum is similar to the sun, which is a black body radiator, but with more photons emitted in the yellow/orange/red areas of the spectrum correlating with a lower color temperature in the 3200 degree Kelvin range.

Fig. B is a spectrograph of an HMI source and while it does have a green spike, it provides a continuous spectrum so desired by many Hollywood film cinemaphotagraphers for its emphasis on the blue spectrum which correlates to its 5500 degree Kelvin color temperature.

Fig. C is a spectrograph of a “white LED” commonly used in many portable LED lights for video use. Clearly we can see a large gap in the blue area of the spectrum just to the right of the violet band. The cause of this: White LEDs are blue/violet LED’s with phosphorus coatings on the diode to simulate the green/yellow/red area of the spectrum. As a consequence to this emission gap in the spectrum, certain objects that are illuminated with this type of source will not reflect back colors not emitted. In addition if the color is not in its spectrum, it cannot be added with a filter (see footnote 1).  This means poor color rendering as compared with continuous spectrum emitting light sources.

Frezzi Energy Systems pioneered portable on camera HMI’s in the 90’s with the introduction of the Mini-Arc 24 Watt HMI, and now the New MRAX-15 Series HMI’s which provide Full Spectrum, daylight balanced output.

The images below demonstrate color rendering differences of HMI and LED light sources. LED sources don’t emit a full spectrum and when comparing colors reflected back, objects lit with a continuous spectrum source render more colors than a non-continuous light source.

The conclusion: for accurate color HMI’s provide the most accurate color rendering of any coninuous daylight balanced (5500K) light source.
plate 2.pdf
plate 1.pdf
Technical Information
Document No. MRAX-Series 15 Watt HMI