# RE: High Intensity Light Question

```Thanks Robert,

A group of researchers are going to place 12-each 1kW quartz lamps on 2
foot centers on a polished aluminum surface to simulate sunlight on an
experiment.

We wanted to insure that the workers and ancillary personnel will not be
overexposed to the high intensity light as well as any associated UV during
the use of this system.

The ACGIH TLV book says that anything greater than 1 cd/cm^2 has to be
evaluated since the TLV may be exceeded above this limit.

Evidently we are not equipped to handle this type of evaluation since we
only have a light meter that reads out in footcandles.

Thanks for your help.

At 11:17 AM 4/2/98 -0600, you wrote:
>
><cd/cm^2> is a unit of luminance (formerly, photometric brightness) and
>is a property of a ray [realistically, the average of a bundle of rays].
> It is the differential luminous flux per unit projected area in the
>direction of the ray and per unit solid.  Thus this unit is its most
>basic form is lumens per cm^2 and per steradian.
>
><footcandles> is a unit of illuminance, i.e., areal flux density.  The
>unit for <footcandles>  is lumens per square foot (incident on an area).
>
>These units are not commensurate, and you cannot convert from one to the
>other.  I suspect that you have mixed up units in some manner or other.
>If you had adequate information about the geometry of incoming luminance
>at a point, you could then calculate the resultant illuminance at that
>point.
>
>Robert E. Levin
>Corporate Scientist
>OSRAM SYLVANIA Development Inc.
>71 Cherry Hill Drive
>Beverly, MA 01915
>(978) 750-1594
>levin@osi.sylvania.com
>
>
>
>
>
>
>>----------
>>Sent: 	Thursday, April 02, 1998 10:30 AM
>>To: 	Multiple recipients of list
>>Subject: 	High Intensity Light Question
>>
>>
>>About 5 years ago I had to figure out how to convert candela/cm^2 to
>>footcandles.  I lost my reference data but seem to remember that
>>one candela/cm^2 approximated 500 footcandles.
>>
>>Does anyone have the formula for this conversion?
>>
>>
>>************************** /^\   /^\ ***********************************
>>Tad  Blanchard            /__ \ /___\   NASA-Goddard Space Flight Center
>>Nat'l Health Svc, Inc          O         Code 205.9, Greenbelt, MD 20771
>>Sr Health Physics Tech        / \                    Phone: 301-286-9157
>>Assistant RSO                /___\                   Fax:   301-286-1618
>>
>>************************************************************************
>>
>
>
************************** /^\   /^\ ***********************************
Tad  Blanchard            /__ \ /___\   NASA-Goddard Space Flight Center
Nat'l Health Svc, Inc          O         Code 205.9, Greenbelt, MD 20771
Sr Health Physics Tech        / \                    Phone: 301-286-9157
Assistant RSO                /___\                   Fax:   301-286-1618