Incandescent lamps dim to below one percent perceived light, which looks like an orange filament glow. The
dimming range of an LED lamp or fixture can
vary greatly from one device to another.
Some may
dim to a minimum level of only 50 percent, while a different product may
dim to one percent. Additionally, manufacturers will quote
measured light numbers, but consumers are familiar with
perceived light.
What is the difference?
Measured light output is the quantifiable value of light measured by a light meter or similar device. This is the dimming percentage indicated on LED product specification sheets.
Perceived light is the amount of light that your eye interprets because of pupil dilation. The eye’s pupil dilates at lower
light levels, causing the amount of light to be perceived
higher than measured (e.g., 20 percent measured light equals 45 percent perceived light). The equation for determining perceived light is to take the square root of the measured light percentage (e.g. √0.2 = 0.45). You need to select the
dimming range of your fixture or lamp that will be suitable for your application. A product that
dims to 20 percent measured light (45 percent perceived) wouldn’t make sense in a
media room, but may be the
energy-saving solution necessary for an
office. If an
LED fixture or lamp spec sheet does not state the dimming range, you should contact the manufacturer for that important piece of information.
It is important to know that the
dimming range of a product is based solely on the driver. The integral driver will determine the
dimmability of a screw-in
LED retrofit lamp and an external driver will determine the
dimmability of an
LED fixture. Each
dimmer may have varying features that will affect your ability to trim out flicker if it exists and minimum load requirements, but it will not affect the dimmability of a product. The driver will determine the low-end light level and the performance. Finally, be aware that the dimming range of a single product may vary based on what control is used.