Photometrics

Photometrics is a lighting science philosophy that describes the measure and distribution of light. Proper photometrics is critical to the performance of a lighting fixture.

Measuring light efficiency

The lumen is a measure of total optical flux or all the energy emanating from a light source. In the past, designers of lighting fixtures needed a convenient way to measure lamp efficiency. So the total optical output of the lamp was converted to lumens and measured in watts (100-watts, 75-watts, etc). But all 100-watt lamps are not the same. For one thing, this measure didn’t account for the color sensitivity of the eye. However, many still view lumens as a good measure of lighting performance when it fact, it is not.

The primary reason is that lamp life has a significant impact on lumen output. For example, in an incandescent lamp, longer life results from the filament running at a lower temperature. Lower Kelvin temperatures are associated with yellow or orange light, while higher Kelvin temperatures are associated with whiter bluer light. This is why a 100-watt movie spotlight, which runs at 3400 Kelvin, will only last 100 hours. While a 100-watt incandescent bulb, which runs at 2700 Kelvin, has a useful life of 2000 hours.

The spotlight produces approximately 30 lumens per input watt, while the incandescent bulb produces 10 lumens per input watt. The tradeoff is lamp efficiency. A lower color-temperature or yellow light has a longer life. On the other hand, when maximum light is required for the given input power, dramatically shorter useful life results.

This same methodology can be applied to HID fixtures (HID, HPS, metal halide), which are more efficient than incandescent lamps.

Thermal management and light efficiency

Until recently LEDs were not as efficient as incandescent and arc lamps. Today however, LEDs can develop up to 110 lumens per input watt. But without proper thermal management, light output diminishes and useful life degrades significantly.

Because LEDs are relatively costly, many manufacturers drive as much current as possible through the light in an effort to increase lumen output. And at these higher wattages LEDs becomes less efficient and very hot.

It’s easy to advertise an LED device that generates a lot of light for the money. But without robust thermal management, cost of ownership is actually higher because the device will degrade in no time at all.

The Relume approach acknowledges that thermal management and photometry are inseparable. Businesses and municipalities making the switch to Relume LED products can be assured that lumen efficiency is maximized and payback times are shortened.

Light distribution and “useable light”

Directionality and efficiency link total light output to useable light, and this is where LEDs have an intrinsic advantage. Because of how they’re made, LEDs do not radiate in a 360-degree ball; their energy is directed. The reference to “useable lumens” takes into account this directionality.

Still, as with virtually all light sources, it is extremely difficult to capture light and efficiently direct it where it is needed. Some manufacturers may use a 400-watt lamp to achieve light requirements on a city street, while a more efficient fixture design will provide the same illuminance using half the power.

Lumen output is irrelevant as long as specifications are fulfilled. Good products can do so efficiently and at low cost. Relume is able to extract more useable light per input watt from any LED than others because of their proprietary thermal management and projection technology techniques. Others require significantly more LEDs, resulting in costly fixtures that are less efficient.

Some suggest that foot-candle (or flux) requirements can be discounted or even halved due to the improved visual acuity derived from LEDs. It’s a weak argument, but is often used by manufacturers whose LED products can’t deliver the requisite light and effectively direct it onto a surface.

Projection Technology™

Relume’s newly developed proprietary Projection Technology™, available on fixtures to be introduced later this year, optically collimates virtually all of the light from every LED into useable, meaningful light. This is accomplished by paying close attention to all of the efficiencies in the lamp.

The combined efficiency of a luminaire is a function of all internal efficiencies (the LED, collimating lens, outer lens, etc). Total system efficiency isn’t the sum of all internal efficiencies; it is the multiple of all efficiencies.

Relume’s new generation lamps begin with a low-cost collimator that captures 92% of all of the light developed by the LED and directs it into a narrow beam. Special free-form faceted reflectors then direct the light accordingly.

Relume’s Projection Technology™ adheres to simple photometric principals:

• Adoption of highly efficient power supplies (93% efficiency)
• Use of highly efficient LEDs (highest lumens per watt in the industry)
• Use of highly efficient collimation optics (93% efficiency)
• Use of highly efficient reflective optics (92% efficiency)

In essence, a Relume fixture is a series of projectors. Each individual LED in the array lights the entire desired area, but in differing proportions and amounts. The result? Light that was previously lost or misdirected is now projected where it is needed most. And less light waste means greater electricity savings and lower maintenance costs.