What’s the best way to determine the light output of a flash unit?
The beam candle power seconds (BCPS) measurement of a flash unit is the most accurate way to determine light output. The higher the BCPS, the greater the light output. However, BCPS will change depending on which reflector is used. The reflector’s angle of illumination and finish will increase or decrease the BCPS. Generally, the narrower the angle, the higher the BCPS, and the shinier the finish the higher the BCPS. If you are comparing flash units made by different manufacturers, the most accurate method is to make a bare bulb BCPS comparison rather than a reflector comparison. Photogenic lists the BCPS measurements for our lights with bare bulb, seven reflectors and three Eclipse umbrellas. Unfortunately, not all flash manufacturers will give you BCPS measurements. The next best method to determine output is guide number. However, guide numbers are not nearly as precise as BCPS. The standard for establishing a guide number is to point an incident flash meter at the center of a light
