![]() ![]() A lamp with a higher S/P ratio will provide sharper vision and better color rendering. The ratio between a lamp’s scotopic luminance and its photopic luminance is called the S/P ratio. When switching between HID and LED, it is better to factor in both kinds of vision. However, LEDs come in a variety of color temperatures, which can help account for the often-problematic disparity between photopic and scotopic vision. We tend to perceive the higher color temperatures of LEDs as brighter than traditional HID light fixtures, such as metal halide or high pressure sodium, when we see them at night. Why is this relevant to selecting an LED fixture? The most common complaint against LEDs is that they are “too bright.” Because of our rods’ sensitivity to the color blue and their strength at low light levels, we can assume that blues and whites will seem more dominant than other colors in low light. We refer to this new range as the mesopic region. New research shows that most visual perception is actually a combined effort between the rods and cones. For years, industry professionals were using this data to measure light levels because of this, the data they were able to provide was limited and skewed. Traditionally, light was only measured and accounted for in the photopic visual range. Photopic vision occurs in high light levels and is controlled primarily by our cones scotopic vision occurs in lower light levels and is controlled primarily by our rods. Visual perception is still broken down into two categories: photopic and scotopic vision. However, thanks to studies conducted at UC Berkeley, we now know the predominant difference between rods and cones is that the latter is sensitive to red, green, and a bit of blue light, while the former is more sensitive to blue light and helps open and close the pupil. It was originally believed that cones were responsible for daytime vision and rods were responsible for nighttime vision. Our eyes perceive light through a complex relationship between photoreceptors called rods and cones. Once you know the mean lamp lumens for your old light fixture, you’ll need to adjust these numbers for visibility, also referred to as visually effective lumens. Adjust Mean Lumen Output for Visible Lumens (Scotopic vs. Many manufacturers will have this information available if you contact them with the HID fixture model number. To account for HID lumen depreciation, the mean lamp lumen data point considers the amount of lumens emitted by an HPS lamp at 50% of its rated life for an MH lamp, we record lumens at 40% of its rated life. High-intensity discharge (HID) lamps start operating with a high initial lumen output that fades over time. Mean lamp lumens is a data point that refers to a lamp’s average lumen output over the course of its life. Let’s pretend we’re beginning with a 250w HPS wall pack with a 2100K lamp.ĭetermine the Mean Lumens Emitted by Your High-Intensity Discharge Lamp While we explain the steps, we will run a mock HID-to-LED upgrade so we can use real data. Once you have the lamp type and wattage, you can move to the next step. ![]() Your wall pack may have the lamp type and wattage information listed in one of three places: on a tag inside the wall pack, on the ballast, or on the lamp itself. Knowing the wattage and lamp type of your current wall pack is the first step in determining which LED wall pack will provide the lighting you want. Since LED systems are so much more efficient than HID systems, and HID fixtures and LED fixtures of the same wattage will not provide the same amount of light, a watt-for-watt replacement of HID to LED will significantly increase your light levels. HID stands for high-intensity discharge HPS, MH, and PSMH (another form of metal halide) all fall under this umbrella. Existing wall packs usually fall under the categories of HID or LED. It is almost impossible to determine which LED wall pack will be the best replacement for your existing wall pack without first knowing the wattage and light source type of your current wall pack. If you’d simply rather not deal with all these calculations yourself, give us a call and we’ll take care of them for you.Ĭonfirm the Wattage and the Type of HID Lamp in Your Wall Pack If you have any questions along the way, feel free to contact us for clarification. To help, we have broken down and cataloged our methodology for making the right selection. Whether switching from high-press sodium (HPS) or metal halide (MH), there are a hundred questions to ask about wattage, delivered light, photopic and scotopic lumens, and more.
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