Lighting Simplified.

When you ask us here at Gross Sales to assist with your current lighting project, we look at it in many different ways, as all projects have unique requirements. We discuss the fittings and controls of course, but we also talk about things like Lumens, efficiency, efficacy, uniformity and such. Most of you fully understand these terms and how they relate to the lighting design, but some don’t so let’s try to shed some light (sorry) on what they mean and how to apply them to your project designs.

Lumens

Lumens, quite simply this means luminous flux or the amount of light that flows from a given light source (lamp). People sometimes get too hung up on initial lamp lumens but different sources suffer lumen depreciation at different rates so this needs to be factored into your thought process. The 1000w metal halide lamp for example has initial lumens up to 120,000 which seems impressive but that figure starts reducing at an alarming rate from the very first time it’s energized whereas a good LED chip with correct thermal management will retain 85% of its initial lumen levels for up to 100,000hrs in many cases.

Footcandles/Lux

Footcandles is the amount of lumens falling in 1 square foot (sq meter for lux), so 50 footcandles means 50 lumens per square foot at the measured plain.

Efficiency

Efficiency is the relationship between a lamps light output and its electrical input, we call this Luminous Efficacy. This is crucial in our decision on what lamp sources to use for many reasons. ASHRAE compliance, LEED points, energy reduction, return on investment, these all require careful consideration on the Luminous Efficacy of the lamp sources. As an example, an MR16 lamp produces about 20 lpw so is not very efficient. A good quality LED chip is now 100 lpw+ so highly efficient.

Uniformity

In design terms, this is the relationship between the minimum and average lighting values on the layout. The aim is to try and get the space as uniform as possible within the laid down guidelines. Metal Halide high bays and post tops were particularly bad at achieving good uniformity due to their excessive nadir dump (hot spots below the fitting) Good quality Fluorescent and LED fittings have all but eliminated this issue for us now, allowing for lower overall light and power density levels due to improved uniformity.

Colour Temperature

The colour temperature of a lamp is measured on a Chromaticity chart in degrees Kelvin. 3500k and below are on the warm or yellow end of the spectrum whereas 5000k and above are on the cool or blue end. In between we have the 3500k to 4500k range which is considered a more natural light and is the range favoured by most of us. Strangely though, the human eye see’s light in the 380-700nm range and is more sensitive to light at around 555nm which is a very yellow portion of the range. This is why high viz vests etc come in those orange/yellow colours, because our eyes pick them out of the background quicker. This should mean that warmer colour temperature lamps are more efficient as our eyes respond to them better but I have not seen any evidence to support that yet.

I hope this helps explain some of the basic criteria we go through when looking at your lighting project, it is what really makes the difference.

Jon Lewis