A customer of ours purchased an expensive LED Fresnel light and was not satisfied with the performance. He returned the light and asked me if I was developing an adjustable LED Fresnel light.
This was my answer to him:
It is unlikely that LED lights will ever match the functionality of an incandescent or HMI Fresnel light. The reason for this is that LEDs are a surface emitter vs. incandescent or HMI, which is a concentrated spot light source. The Fresnel is a lens that works by focusing (or de-focusing) a spot source of light. In order to increase the light output of an LED you need to increase the surface area of the emitter. A current 200 watt LED has a surface area of about 4 square inches. I have tested many of these products and they do not perform very well. The issue is that when you attempt to focus the light, the intensity of the light does not increase. In some designs, the light output decreases as you focus the light. Therefore, the throw of the light does not improve when you focus the light. The effect of these Fresnel adjustments is similar to barndoor or flag adjustment of masking the outer light.
All of the Fresnels that I have tested are large, bulky and not very portable. Their best use is in a studio, not on location. Most of these products include DMX control, which is a studio requirement.
In order for an LED to be able to produce the equivalent lumen output in a tiny spot like an HMI, the lumen/watt factor would need to increase about 1000-5000 times. At the current advances in the LED technology, the rate of the improvement in lumen/watt is about 25% per year. If this rate increase rate is sustainable (and this is not likely), it would take many lifetimes for an Fresnel LED to be equivalent to an HMI.
I suggested to this customer, who owns an ALZO 3000 LED light, that we have a Fresnel barndoor accessory that works well, as it focuses the light of the LED and increases the throw at very low cost.
