May 29, 2024

ACGIH limits when tilting Ushio Care222 modules

Application Note

ACGIH limits when tilting Ushio Care222 modules

By Holger Claus

May 2024

1. Introduction

Certain fixtures using Care222 modules are designed in a way that the fixture can be tilted in the application. In such case it is very difficult to predict the doses that will be received by eye and skin and to determine if such doses will be below ACGIH limits. It is also of interest to know how such tilting will influence the achievable fluence rate in a room. For the more common installation of a straight down (no tilt) ceiling fixture it has already been established that if the skin dose is within ACGIH limits, the eye dose will be very significantly below (eye) ACGIH limit [1].

The following graphs show data of simulations of skin and eye doses at a 1.9m height (UL8802) for Ushio B1 (60 deg angle) and B1.5 (120deg, diffuse) modules and example data of fluence rates for a 5x5x3m room depending on fixture height and tilt angle. The lamp was “mounted” at 1m away from a wall, at various heights, and the lamp was tilted towards the opposite wall.

2. B1 module

As can be seen from the graphs, it is clear that the ACGIH limits are exceeded in almost every scenario. It is necessary to either dim the lamp (On/Off duty cycling) or prevent overexposure through other means (occupancy detection).

3. B1.5 module

As can be seen, tilting a B1.5 module will under no circumstances exceed ACGIH levels. However, the fluence rates in the room are very significantly lower than with the B1 module.

An example of the spatial distributions of skin and eye doses are shown below for a fixture height of 2.3 meters and a tilt angle of 50 degrees with a B1.5 module.


The author would like to thank Vivian Belenky (Columbia University) for providing the simulation software that has been used to obtain the above data.


The raw data are available in this embedded file:

B modules tilting data.xlsx

Table 1


[1] H. Claus, "EXPECTED ACGIH EYE EXPOSURE WHEN USING 222NM CEILING MOUNTED SOURCES," Optical Radiation News, Summer/Fall 2022.

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