# HID Equivalency

When looking to create a more efficient and reliable lighting plan, one of the easiest ways to improve on matters such as lumen output and wattages consumed is to switch to LED. While most lighting solutions can be retrofitted to accommodate LED technology, certain types of fixtures will be impossible to convert to LED and will need to be replaced altogether. If you are dealing with an older model of a high-intensity discharge (HID) fixture and looking to replace it with a newer LED option, there are a few things you need to know. Let’s take a closer look at the matter of HID equivalency to help you make the right choice.

### Why do you need to figure out the equivalency?

Many people wrongly assume they can simply plug in LED lamps into their existing HID fixture. However, the lamps will not start because the operation methods don’t align properly. Another mistake people often make with this area of lighting is that they assume the lumen output of their HID should be replaced with an LED of the same or higher lumen output. This isn’t quite how it works since LED technology tends to produce a more concentrated lumen output that can overpower the space if you are used to HID fixtures.

### How do I figure out the equivalency?

The most important thing to look at is the type of HID fixture you currently have in place. This category of fixtures can include types such as high-pressure sodium and metal halide. If you have either of those types of fixtures, you have an HID fixture.

When looking at HID equivalency, the goal is to find the LED alternative comparable to your current fixture without losing your calculated lumen output per square foot. The only way to do this is to look at the lumens. The lumens of an HID fixture tend to be less concentrated in output whereas an LED offers a constant stream of lumens without fluctuations, so it is important to calculate the difference between the two fixtures. This is called lumen deprecation. To calculate lumen deprecation, you can contact the manufacturer of the solution. Many HID fixtures will have anywhere from 40% to 50% lumen deprecation over the life of a fixture.

A main complaint when people switch from an HID fixture to an LED is that LED is too bright. This can happen because you selected the same lumen output in LED as the HID without factoring in for variances in output as previously mentioned. It can also be a result of failing to recognize the different ways our eyes visualize illumination. For instance, it was believed that our ability to recognize high light levels was controlled by the cones of our eyes whereas vision related to lower light levels was perceived through the rods of eyes, but scientists now note that both areas of the eye are used together to perceive light based on the wavelength color and not just the light levels. Why does this matter? It matters because many people claim LED is too “bright” when switching from HID, but the real issue is a failure to calculate the ratio between the two types of light perceived by the eyes in relation to what is considered visible lumens. These two types of light are called the scotopic luminance and photopic luminance while the difference between the two in any fixture is called the S/P ratio. To figure out which choice is right for you, you will need to determine the S/P ratio and then multiply it by the mean lumens of the solution. This will give you the number of visible lumens of any selected fixture type. Once you know how many visible lumens are needed for your space based on these calculations, you can easily find the HID equivalency for LED solutions.

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